Note: Descriptions are shown in the official language in which they were submitted.
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Ophthalmic Wavefront Sensor Operating in Parallel Sampling and Lock-In
Detection Mode
Technical Field of the Invention
100021 One or more embodiments of the present invention relate
generally to
wavefront sensors for determining the refractive state and wavefront
aberrations of an eye. In
particular, the invention is an apparatus for determining the refractive state
and wavefront
aberrations of an eye during ophthalmic surgery.
Background of the Invention
100031 Wavefront sensors are devices used to measure the shape of a
wavefront of
light (see, for example, US4141652 and US5164578). In most cases, a wavefront
sensor
measures the departure of a wavefront from a reference wavefront or an ideal
wavefront such
as a plane wavefront. A wavefront sensor can be used for measuring both low
order and high
order aberrations of various optical imaging systems such as the human eye
(see for example,
US6595642; J. Liang, et al. (1994) "Objective measurement of the wave
aberrations of the
human eye with the use of a Hartmann¨Shack wave-front sensor," J. Opt. Soc.
Am. A 11,
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1949---1957; T. Dave (2004) "Wavefront aberrometry Part 1: Current theories
and concepts"
Optometry Today, 2004 Nov. 19, page 41-45). Furthermore, a wavefront sensor
can also be
used in adaptive optics in which the distorted wavefront can be measured and
compensated in
real time, using, for example, an optical wavefront compensation device such
as a deformable
mirror (see for example UShttp://patft. uspto.govinetacgilnph-
Parser?Sect I ¨PTO &Seet2¨HITOIT&A=PALLA:p¨ I
&u=%2Fuetalum1;102FIYIV,v02Fsrehnu
m.htm&r=: I &f-G&I0&s I ,,,690076.P.N AS1).N/6890076M-6 PN /6890076 -
hW/huhttp:S/patft.uspto.go'netacgi/nph-
I PTO1
Mil :; ''.68900 -
h2#h26890076, US6910770 and US6964480). As a result of such compensation, a
sharp
image can be obtained (see for example US 5777719).
100041 The term "phakic eye" refers to an. eye including its natural
lens, the term.
"aphakic eye" refers to an eye with its natural lens removed and the term
"pseudo-phakic
eye" refers to an eye with an artificial lens implanted. Currently, most
wavefront sensors for
measuring the aberration of a human eye are designed to only cover a limited
diopter range of
about -20D to +20D for a phakic or pseudo-phakic eye. In addition, they are
also designed to
operate in a relatively dark environment when the eye wavefront is to be
measured.
100051 During ophthalmic surgeries that affect refraction, it is
desirable to know the
refractive state of the eye as the surgery is on-going so that a continuous
feedback can be
provided to the surgeon (see for example, US6793654, US7883505 and US7988291).
This is
especially the case in cataract surgery in which the natural lens of the eye
is replaced by a
synthetic lens. In such a case, the surgeon prefers to know the refractive
state of the eye in the
phakic, aphakic and pseudo-phakic stage in order to select a synthetic lens,
confirm if its
refractive power is correct after the natural lens is removed, and also to
confirm emmetTopia
or other intended diopter values after the synthetic lens is implanted.
Therefore, there is a
need for a wavefront sensor to cover a larger diopter measurement range and
also to allow the
surgeon to measure the refractive state of the eye, with a specified degree of
precision, at not
only the phakic and pseudo-phakic state but also at the aphakic state.
100061 Also during ophthalmic surgery, the eye is illuminated with
unpolarized
broadband (white) light from the surgical microscope so the surgeon can see
the patient eye
through the microscope. This illuminating light is also directed into the eye
of the patient,
scattered from the retina, and returned to the surgical microscope. A
wavefront sensor
coupled to the surgical microscope receives both its intended returned
wavefront
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measurement light and the broadband illumination from the surgical microscope.
The
microscope illumination light source is generally not designed to produce a
sufficiently-small
effective source of light at the retina that is required to generate a
wavefront that reveals the
patient's refractive state. Because of this, any illumination light from the
surgical microscope
that is accepted by the wavefront sensor can lead to incorrect information
about the patient's
refractive state. Therefore, there is also a need for an ophthalmic wavefront
sensor that is
immune to influence of the illumination light from a surgical microscope.
[0007] Commercially available wavefront sensors for cataract surgery,
such as the
ORange intraoperative wavefront aberrometer from WaveTec Vision (see for
example,
US6736510), do not provide continuous feedback, are limited in refractive
diopter range
coverage and also are not immune to interference from the illumination light
of the surgical
microscope. In fact, in order to get a sufficiently precise and accurate
refraction measurement
using the ORange wavefront sensor, the surgeon has to pause the surgical
procedure, turn off
the illumination light of the surgical microscope, and has to capture multiple
frames of data,
which leads to additional time up to several minutes added to the cataract
refractive surgery
time.
Summary of the Invention
[0008] One embodiment relates to an ophthalmic wavefront sensor
comprising: a light
source configured to receive a reference signal oscillating or pulsing at a
reference frequency
and to generate a beam of light formed by pulses of light at the reference
frequency; a beam
directing element configured to launch the beam of light from the light source
into a patient
eye and where a portion of the beam of light returned from the patient eye
forms an object
wavefront in the form of light pulses at the reference frequency; an optical
wavefront relay
system, configured to relay an object wavefront from an object plane located
at the anterior
portion of a patient eye to a wavefront image plane along a beam path that can
guide an
incident wavefront relay beam having a large diopter range at the object plane
to the
wavefront image plane; an array of high frequency response position sensing
devices with
each position sensing device configured to detect the amount of deflection of
an image spot
centroid from a reference position and to output a measurement signal
indicating the amount
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of deflection; an array of sub-wavefront sampling elements, disposed before
the array of high
frequency response position sensing devices and at the wavefront image plane,
with each
sampling element in the array of sub-wavefront sampling elements configured to
sample a
sub-wavefront of the relayed wavefront and to focus a sampled sub-wavefront
onto a
corresponding high frequency response position sensing device in the array of
high frequency
response position sensing devices, where the sub-wavefront sampling elements
are physically
spaced from each other in such a way that each sampled sub-wavefront of a high
diopter
range object wavefront is focused only on the corresponding high frequency
response position
sensing device corresponding to the sub-wavefront sampling element; and an
electronic
frequency-sensitive detection system coupled to receive the reference signal
and the
measurement signal, with the electronic frequency-sensitive detection system
configured to
indicate only the magnitude of a frequency component of the measurement signal
at about the
reference frequency so that all noise signals, at frequencies different from
the reference
frequency can be suppressed.
[0009] One feature is the use of two cascaded wavefront relays with the
second relay
having a Fourier transform plane where the wavefront relay beam is made to
reside within a
certain space volume when the wavefront from the eye changes over a large
diopter range. A
beam scanner/deflector is disposed at the Fourier transform plane of the
second relay to
angularly scan the beam so that the relayed wavefront at the final wavefront
image plane can
be transversely shifted relative to an array of a number of sub-wavefront
sampling elements.
A corresponding number of PSDs are disposed behind the wavefront sampling
elements to
operate in lock-in detection mode in synchronization with a pulsed light
source that generate
the wavefront from the eye. With transverse wavefront shifting, any portion of
the relayed
wavefront can be sampled and the spatial resolution of wavefront sampling can
also be
flexibly controlled.
[0010] Another feature for use during ophthalmic surgery is a light
source for
generating the wavefront that varies in output between at least two states
with the wavefront
returning from the eye of a patient detected in each of the "bright" state and
"dark" state, to
enable the rejection of signals from light other than the measurement light.
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100111 Another feature is detecting, in parallel, portions of the
wavefront using a
number of high-speed PSDs that can all be operated in lock-in detection mode
in
synchronization with the light source at a frequency above the 1/f noise range
so that DC and
low frequency background noises can be effectively filtered out.
[0012] Another feature is performing active parallel wavefront sampling.
The active,
parallel wavefront sampling elements can be controlled in terms of their
position, sub-
wavefront sampling aperture size, focusing power, and on/off state.
[0013] Still another feature enhances the diopter coverage rangeby
having the sub-
wavefront sampling elements spaced apart wide enough so that there is no cross
talk between
the wavefront sampling elements over a large refractive error measurement
diopter range. In
another example, only a certain number of sub-wavefronts well separated from
each other are
sampled by activating a subset of the sub-wavefront sampling elements and also
by enabling
only a corresponding number of position sensing devices/detectors (PSDs) to
avoid cross talk.
In still another example, the PSDs and the sub-wavefront sampling elements can
be activated
to respectively change their longitudinal position and/or their focusing power
in response to
the patient's refractive state such that the sub-wavefront tilt sensitivity
for each PSD can be
dynamically adjusted. In addition, the transverse position of the PSDs can
also be adjusted in
response to the patient's refractive state such that each PSD is positioned at
the best transverse
position to provide an optimized centroid position response.
[0014] Still another feature is utilizing sequentially scanning or shifting
the whole
wavefront so that while the parallel sub-wavefront sampling elements and the
position sensing
devices/detectors (PSDs) are fixed in space, any portion of the incident
wavefront can be
sampled. In another aspect, the scanner/deflector tracks the eye and shifts
the wavefront
returned from the patient's eye with automatic adjustment of the shift so that
depending on
the pupil size, position, and the diopter value of the wavefront from the eye,
only certain
desired portions of the wavefront within the patient's pupil, such as the
central 3 ¨ 4mm
diameter area, are sampled.
[0015] Still another feature is utilizing timely reporting of the
measured eye refraction
in the sense that there is low latency between any change in the refractive
state and its report
by the instrument. This is achieved by averaging the detected wavefront
aberration data over a
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desired period and updating the qualitative and/or quantitative measurement
result overlaying
a live eye image with a desired update rate.
[0016] Still another feature provides accurate measurements over a
large diopter range
of refractive errors that occur during ophthalmic surgery, for example those
errors that occur
when the natural lens of the eye has been removed but before replacement with
an artificial
lens. These accurate measurements can be achieved in a number of ways. One
example is to
design the optics to dynamically adjust the sensitivity or the slope of the
sub-wavefront tilt
response curve by actively changing the distance between the sub-wavefront
sampling
elements and the position sensing devices/detectors, or by actively changing
the focal length
of the sub-wavefront focusing lenses. Another example is to dynamically offset
the spherical
refractive diopter value of the wavefront at an intermediate conjugate
wavefront image plane
using a spherical diopter value offsetting element such as a focal length
variable lens.
[0016a] There is described an ophthalmic wavefront sensor comprising:
a light source
configured to receive a reference signal oscillating or pulsing at a reference
frequency and to
generate a beam of light formed by pulses of light at the reference frequency;
a beam
directing element configured to launch the beam of light from the light source
into a patient
eye and where a portion of the beam of light returned from the patient eye
forms an object
wavefront in the form of light pulses at the reference frequency; a first
optical wavefront relay
system, configured to relay an object wavefront from a first object plane
located at the
anterior portion of a patient eye to a first wavefront image plane along a
first beam path that
can guide an incident wavefront relay beam having a large diopter range at the
object plane to
the first wavefront image plane; a second optical wavefront relay system
having a second
object plane located at the first wavefront image plane, configured to further
relay the object
wavefront from the second object plane to a second wavefront image plane along
a second
beam path that can guide the incident wavefront relay beam having a large
diopter range at
the first object plane to the second wavefront image plane; an array of high
frequency
response position sensing devices with each position sensing device configured
to detect the
amount of deflection of an image spot centroid from a reference position and
to output a
measurement signal indicating the amount of deflection; an array of sub-
wavefront sampling
elements, disposed before the array of high frequency response position
sensing devices and
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at the second wavefront image plane, with each sampling element in the array
of sub-
wavefront sampling elements configured to sample a sub-wavefront of the
relayed wavefront
and to focus a sampled sub-wavefront onto a corresponding high frequency
response position
sensing device in the array of high frequency response position sensing
devices, where the
sub-wavefront sampling elements are physically spaced from each other in such
a way that
each sampled sub-wavefront of a high diopter range object wavefront is focused
only on the
corresponding high frequency response position sensing device corresponding to
the sub-
wavefront sampling element; and an electronic frequency-sensitive detection
system coupled
to receive the reference signal and the measurement signal, with the
electronic frequency-
sensitive detection system configured to indicate only the magnitude of a
frequency
component of the measurement signal at about the reference frequency so that
all noise
signals, at frequencies different from the reference frequency can be
suppressed.
[0016b] There is described an ophthalmic wavefront sensor adapted to
couple to an
ophthalmic microscope, comprising: a light source configured to receive a
reference signal
oscillating or pulsing at a reference frequency and to generate a beam of
light formed by
pulses of light at the reference frequency; a first beam directing element
configured to launch
the beam of light from the light source into a patient eye and where a portion
of the beam of
light returned from the patient eye forms an object wavefront in the form of
light pulses at the
reference frequency; an imaging sensor configured to provide a live eye
anterior image; a
second beam directing element configured to provide an optical path for eye
imaging; an
optical wavefront relay system, configured to relay an object wavefront from
an object plane
located at the anterior portion of a patient eye to a wavefront image plane
along a beam path
that can guide an incident wavefront relay beam having a large diopter range
at the object
plane to the wavefront image plane; an array of high frequency response
position sensing
devices with each position sensing device configured to detect the amount of
deflection of an
image spot centroid from a reference position and to output a measurement
signal indicating
the amount of deflection; an array of sub-wavefront sampling elements,
disposed before the
array of high frequency response position sensing devices and at the wavefront
image plane,
with each sampling element in the array of sub-wavefront sampling elements
configured to
sample a sub-wavefront of the relayed wavefront and to focus a sampled sub-
wavefront onto a
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corresponding high frequency response position sensing device in the array of
high frequency
response position sensing devices, where the sub-wavefront sampling elements
are physically
spaced from each other in such a way that each sampled sub-wavefront of a high
diopter
range object wavefront is focused only on the corresponding high frequency
response position
sensing device corresponding to the sub-wavefront sampling element; and an
electronic
frequency-sensitive detection system coupled to receive the reference signal
and the
measurement signal and coupled to the image sensor, with the electronic
frequency-sensitive
detection system configured to indicate only the magnitude of a frequency
component of the
measurement signal at about the reference frequency so that all noise signals,
at frequencies
different from the reference frequency can be suppressed.
[0016c] There is described an ophthalmic wavefront sensor adapted to
couple to an
ophthalmic microscope, comprising: a light source configured to receive a
reference signal
oscillating or pulsing at a reference frequency and to generate a beam of
light formed by
pulses of light at the reference frequency; a first beam directing element
configured to launch
the beam of light from the light source into a patient eye and where a portion
of the beam of
light returned from the patient eye forms an object wavefront in the form of
light pulses at the
reference frequency; an imaging sensor configured to provide a live eye
anterior image; a
second beam directing element configured to provide an optical path for eye
imaging; a first
optical wavefront relay system, configured to relay an object wavefront from a
first object
plane located at the anterior portion of a patient eye to a first wavefront
image plane along a
first beam path that can guide an incident wavefront relay beam having a large
diopter range
at the object plane to the first wavefront image plane; a second optical
wavefront relay system
having a second object plane located at the first wavefront image plane,
configured to further
relay the object wavefront from the second object plane to a second wavefront
image plane
along a second beam path that can guide the incident wavefront relay beam
having a large
diopter range at the first object plane to the second wavefront image plane;
an array of high
frequency response position sensing devices with each Position sensing device
configured to
detect the amount of deflection of an image spot centroid from a reference
position and to
output a measurement signal indicating the amount of deflection; an array of
sub-wavefront
sampling elements, disposed before the array of high frequency response
position sensing
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devices and at the second wavefront image plane, with each sampling element in
the array of
sub-wavefront sampling elements configured to sample a sub-wavefront of the
relayed
wavefront and to focus a sampled sub-wavefront onto a corresponding high
frequency
response position sensing device in the array of high frequency response
position sensing
devices, where the sub-wavefront sampling elements are physically spaced from
each other in
such a way that each sampled sub-wavefront of a high diopter range object
wavefront is
focused only on the corresponding high frequency response position sensing
device
corresponding to the sub-wavefront sampling element; and an electronic
frequency-sensitive
detection system coupled to receive the reference signal and the measurement
signal, with the
electronic frequency-sensitive detection system configured to indicate only
the magnitude of a
frequency component of the measurement signal at about the reference frequency
so that all
noise signals, at frequencies different from the reference frequency can be
suppressed.
[0016d] There is described an ophthalmic wavefront sensor comprising:
an optical
wavefront relay system, configured to relay an object wavefront from an object
plane located
at the anterior portion of a patient eye to a wavefront image plane along a
beam path that can
guide an incident wavefront relay beam having a large diopter range at the
object plane to the
wavefront image plane; a beam scanner or deflector disposed along the beam
path, configured
to fully intercept and scan the wavefront relay beam in two dimensions; an
array of position
sensing devices with each position sensing device configured to detect the
amount of two
dimensional deflection of an image spot centroid from a reference position and
to output a
measurement signal indicating the amount of two dimensional deflection; and an
array of sub-
wavefront sampling elements, disposed before the array of position sensing
devices and at the
wavefront image plane, with each sampling element in the array of sub-
wavefront sampling
elements configured to sample a sub-wavefront of the relayed wavefront and to
focus a
sampled sub-wavefront onto a corresponding position sensing device in the
array of position
sensing devices, where the sub-wavefront sampling elements are physically
spaced from each
other in such a way that each sampled sub-wavefront of a high diopter range
object wavefront
is focused only on the corresponding position sensing device corresponding to
the sub-
wavefront sampling element.
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[0016e] There is described an ophthalmic wavefront sensor comprising:
a first optical
wavefront relay system, configured to relay an object wavefront from a first
object plane
located at the anterior portion of a patient eye to a first wavefront image
plane along a first
beam path that can guide an incident wavefront relay beam having a large
diopter range at the
first object plane to the first wavefront image plane; a second optical
wavefront relay system
having a second object plane located at the first wavefront image plane,
configured to further
relay the object wavefront from the second object plane to a Fourier transform
plane and to a
second wavefront image plane along a second beam path that can guide the
incident
wavefront relay beam having a large diopter range at the first object plane to
the second
wavefront image plane; a beam scanner or deflector disposed at the Fourier
transform plane,
configured to fully intercept and scan the wavefront relay beam; an array of
position sensing
devices with each position sensing device configured to detect the amount of
deflection of an
image spot centroid from a reference position and to output a measurement
signal indicating
the amount of deflection; and an array of sub-wavefront sampling elements,
disposed before
the array of position sensing devices and at the second wavefront image plane,
with each
sampling element in the array of sub-wavefront sampling elements configured to
sample a
sub-wavefront of the relayed wavefront and to focus a sampled sub-wavefront
onto a
corresponding position sensing device in the array of position sensing
devices, where the sub-
wavefront sampling elements are physically spaced from each other in such a
way that each
sampled sub-wavefront of a high diopter range object wavefront is focused only
on the
corresponding position sensing device corresponding to the sub-wavefront
sampling element.
[0016f] There is described an ophthalmic wavefront sensor comprising:
a light source
configured to receive a reference signal oscillating or pulsing at a reference
frequency and to
generate a beam of light formed by pulses of light at the reference frequency;
a beam
directing element configured to launch the beam of light from the light source
into a patient
eye and where a portion of the beam of light returned from the patient eye
forms an object
wavefront in the form of light pulses at the reference frequency; an optical
wavefront relay
system, configured to relay an object wavefront from an object plane located
at the anterior
portion of a patient eye to a wavefront image plane along a beam path that can
guide an
incident wavefront relay beam having a large diopter range at the object plane
to the
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wavefront image plane; an array of high frequency response position sensing
devices with
each position sensing device configured to detect the amount of deflection of
an image spot
centroid from a reference position and to output a measurement signal
indicating the amount
of deflection; and an array of sub-wavefront sampling elements, disposed
before the array of
high frequency response position sensing devices and at the wavefront image
plane, with each
sampling element in the array of sub-wavefront sampling elements configured to
sample a
sub-wavefront of the relayed wavefront and to focus a sampled sub-wavefront
onto a
corresponding high frequency response position sensing device in the array of
high frequency
response position sensing devices, where the sub-wavefront sampling elements
are physically
spaced from each other in such a way that each sampled sub-wavefront of a high
diopter
range object wavefront is focused only on the corresponding high frequency
response position
sensing device corresponding to the sub-wavefront sampling element.
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100171 These and other features and advantages of the example
embodiments will
become more readily apparent to those skilled in the art upon review of the
following detailed
description of the preferred embodiments taken in conjunction with the
accompanying
drawings. Each of these features can be used singly or in combination and with
any of the
embodiments described herein.
Brief Description of the Drawing
100181 Fig. 1 shows a schematic diagram of the sequential wavefront
sensor disclosed
in co-assigned US7445335.
100191 Fig. 2 shows an improved optical configuration as disclosed in co-
assigned
US20120026466.
100201 Fig. 3a shows one embodiment of an example wavefront sensor, in
which a
pulsed light source is synchronized with an array of position sensing
devices/detectors to
enable the sensor to work in both parallel sampling and also lock-in detection
mode.
100211 Fig. 3b shows a lenslet array of a typical Shack-Hartmann wavefront
sensor
with a corresponding array of position sensing devices/detectors and the
maximum diopter
measurement range that can be achieved without cross talk.
100221 Fig. 3c shows an example arrangement of the sub-wavefront
sampling
elements with a corresponding array of position sensing devices/detectors and
the maximum
diopter measurement range that can be achieved without cross talks.
100231 Fig. 4 is a block diagram showing one example embodiment of a
lock-in
detection amplifier.
100241 Fig. 5 shows one example of sequential transverse wavefront
shifting or
scanning as applied to the optical configuration of Fig. 3a.
100251 Fig. 6 shows another embodiment of the wavefront sensor of Fig. 3a,
in which
an 8-f wavefront relay configuration is combined with a small beam scanner to
enable
practical sequential wavefront scanning in addition to parallel wavefront
sampling and lock-
in detection.
100261 Fig. 7 shows one example of sequential transverse wavefront
shifting or
scanning as applied to the optical configuration of Fig. 6.
100271 Fig. 8 shows an example of the incorporation of a fixation
light source and an
eye image sensor into the configuration of Fig. 6.
100281 Fig. 9 shows an example of the integration of the presently
disclosed
wavefront sensor with a surgical microscope.
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100291 Fig. 10 shows an example of the integration of the presently
disclosed
wavefront sensor with a slit-lamp bio-microscope.
Detailed Description
100301 Reference will now be made in detail to various example embodiments
illustrated in the accompanying drawings. While the invention will be
described in
conjunction with these embodiments, it will be understood that it is not
intended to limit the
invention to any embodiment. On the contrary, it is intended to cover
alternatives,
modifications, and equivalents as may be included within the spirit and scope
of the invention
as defined by the appended claims. In the following description, numerous
specific details are
set forth in order to provide a thorough understanding of the various
embodiments. However,
the present invention may be practiced without some or all of these specific
details. In other
instances, well known process operations have not been described in detail in
order not to
unnecessarily obscure the present invention. Further, each appearance of the
phrase an
"example embodiment" at various places in the specification does not
necessarily refer to the
same example embodiment.
100311 Most prior art ophthalmic wavefront sensors for human eye
wavefront
measurements use a two dimensional CCD or CMOS image sensor for wavefront
information
collection. For examples, a typical Harttnann-Shack wavefront sensor (see for
example,
US5777719, 6199986 and 6530917) uses a two dimensional lenslet array and a two
dimensional CCD or CMOS image sensor. A Tscheming wavefront sensor (see for
example,
Mrochen et al., "Principles of Tscherning Abeffometry," J of Refractive
Surgery, Vol. 16,
September/October 2000) projects a two dimensional dot array pattern onto the
retina and
uses a two dimensional CCD or CMOS image sensor to obtain the image of the two
dimensional dot pattern returned from the eye to extract the wavefront
information. A Talbot
wavefront sensor uses a cross grating and a CCD or CMOS image sensor placed at
the self-
imaging plane of the cross grating (see for example U S6781681) to extract the
wavefront
information. A Talbot Moire wavefront sensor (see for example, US6736510) uses
a pair of
cross gratings with mutual rotational angle offset and a CCD or CMOS image
sensor to
obtain an image of the Moire pattern to extract the wavefront information. A
phase diversity
wavefront sensor (see for example US7554672 and US20090185132) uses a
diffraction lens
element and a two dimensional CCD or CMOS image sensor to obtain images
associated
with different diffraction orders to extract the wavefront information.
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100321 Due to the large amount of data that needs to be collected by
the two
dimensional image sensor and to the limit in the frame rate resulting from the
clock rate
and/or the data transfer rate over an electronic data transfer line such as a
USB cable, the
image sensors used in all these prior art wavefront sensor devices can only
operate with a
relatively low frame rate (typically at 25 to 30 frames per second) and hence
are sensitive to
DC or low frequency background noise. A.s a result, these prior art wavefront
sensors
generally can only function in a relatively dark environment in order to
reduce noise from DC
or low frequency background/ambient light.
100331 In addition, the diopter measurement range of these ophthalmic
wavefront
sensors are generally limited to within 20D due in large part to a compromise
in the spacing
or pitch of the fixed grid wavefront sampling elements, which determines the
wavefront tilt
sensitivity, the wavefront diopter measurement range, and the wavefront
measurement spatial
resolution.
100341 Another wavefront sensor technology based on laser beam ray
tracing (see for
example US6409345 and US6932475) does not absolutely require the use of a two
dimensional CCD or CMOS image sensor for wavefront information extraction.
However, a
commercial product (iTrace from Tracey Technologies) has a limited measurement
range of
only :I:15D, and still requires a dark environment for wavefront measurement.
100351 Co-assigned US7445335 discloses a sequential wavefront sensor
that
sequentially shifts the entire wavefront to allow only a desired portion of
the wavefront to
pass through a wavefront sampling aperture. This wavefront sensor employs lock-
in detection
to reject DC or low frequency optical or electronic noise such as from
background light or
electronic interferences by pulsing the light source used for generating the
wavefront from
the eye and synchronizing it with a high frequency response position sensing
device/detector
(such as a quadrant detector). Therefore, this wavefront sensor does not
require a dark
environment for wavefront measurement, and is extremely suitable for
continuous real time
intra-operative refractive surgeries with the illumination light of a surgical
microscope
remaining always in the "on" state. Sequentially sampling a wavefront
completely removes
any potential cross talk issue, which therefore provides the possibility of a
large wavefront
measurement dynamic range. However, the optical configuration of US7445335 is
not ideal
for covering a large diopter range as it needs a beam scanner with a
relatively large beam
interception area. Another co-assigned U.S. patent application (US20120026466)
discloses
improved optical configurations over US7445335. These improved configurations
can. allow
the use of a relatively small and commercially available light beam scanner
(such as a MEMS
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scanner) to scan the whole object beam from an eye over a large diopter range
(up to 30D),
and consequently, refraction of the eye in even the aphaldc state can be
adequately covered.
By flexibly shifting the wavefront, any portion of the wavefront can be
sampled and thus high
spatial resolution can also be achieved.
100361 However, due to eye safety requirement, there is a limit to the
optical energy
that can be delivered within a given time to a patient eye. Therefore, even
with the pulsing of
the light source and the lock-in detection approach to boost up signal to
noise ratio, if one
wants to sample a large number of spatial portions of a wavefront returned
from an eye, the
wavefront measurement update rate can be limited. On the other hand, if one
wants to have
high wavefront measurement update rate, the maximum number of spatial sampling
points
can be limited. There is thus a need to further improve the performance of
such a wavefront
sensor operating in lock-in detection mode.
100371 In accordance with one or more embodiments of the present
invention, a
number of parallel wavefront sampling elements are combined with a
corresponding number
of image or light spot position sensing devices/detectors (PSDs) that all
operate in lock-in
detection mode in synchronization with the pulsing of the light source at a
frequency above
the 1/f noise frequency range. Each PSD has a sufficiently high frequency
response so that
DC or low frequency background light generated noise can be substantially
filtered out and
the signal to noise ratio can be boosted.
100381 In addition to sampling the wavefront in parallel, the physical
spacing of the
parallel wavefront sampling elements is designed so that there is no cross
talk within, a
desired eye refractive error diopter coverage range, Furthermore, in order to
sample any
portion or segment of a wavefront, the wavefront can also be sequentially
shifted relative to
the wavefront sampling elements using similar approaches as disclosed in co-
assigned patent
US7445335 and patent application US20120026466.
100391 Fig. 1 shows a schematic diagram of the sequential wavefront
sensor disclosed
in co-assigned US7445335. A narrow beam of light from a light source 134 is
directed to the
retina of an eye 138 through a beam-directing element 136 such as a beam
splitter. An object
beam of light originating from the retina of the eye, having a wavefront 102
when leaving the
eye, is focused by the first lens 104. The object wavefront beam travels
through a polarization
beam. splitter (PBS) 106 arranged in such a manner that its pass-through
polarization
direction is aligned with the desired polarization direction of the object
light beam. As a
result, a linearly polarized object beam will pass through the PBS 106. A
quarter-wave plate
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108 is placed behind the PBS 106 with the fast axis oriented so that a
circularly polarized
light beam is emerged after the beam passes through the quarter-wave plate
108.
100401 The object light beam that carries the wavefront information
from the eye is
focused on the reflective surface of a tilted scanning mirror 112, which is
mounted on a
motor shaft 114. The object light beam reflected by the mirror is changed to a
direction that is
dependent on the tilting angle of the scan mirror 112 and the rotational
position of the motor
114. The reflected beam is still circularly polarized, but the circular
polarization rotation
direction will be changed from left hand to right hand or from right hand to
left hand. Hence,
upon passing through the quarter-wave plate 108 for a second time on its
return path, the
beam becomes linearly polarized again, but with its polarization direction
rotated to an
orthogonal direction with respect to that of the original incoming object
beam. Therefore, at
the polarization beam splitter 106, the returned object beam will be mostly
reflected to the
left as shown by the dashed light rays in Fig. 1.
100411 A second lens 116 is placed on the left next to the PBS 106 to
collimate the
reflected object beam and to produce a replica of the original input wavefront
(124) at the
plane of the wavefront sampling aperture 118. Due to the tilting of the scan
mirror, the
replicated wavefront 124 is transversely shifted. An aperture 118 is placed in
front of a sub-
wavefront focusing lens 120 to select a small portion of the replicated
wavefront 124. The
sub-wavefront focusing lens 120 focuses the selected sub-wavefront onto a
position sensing
device/detector 122, which is used to determine the centroid of the focused
light spot
generated from the sequentially selected sub-wavefronts. By rotating the motor
114 and
changing the tilting angle of the scan mirror 112, the amount of radial and
azimuthal shift of
the replicated wavefront can be controlled such that any potion of the
replicated wavefront
can be selected to pass through the aperture 118 in a sequential way. As a
result, the overall
wavefront of the original incoming beam can be characterized as in the case of
a standard
Hartmann-Shack wave-front sensor with the exception that the centroid of each
sub-
wavefront is now obtained in a sequential rather than a parallel manner.
100421 As can be seen in Fig. 1, by controlling the tilt angle of the
scan mirror and the
rate of pulsing the light source, any portion of the wavefront can be sampled.
In addition, the
electronic control and detection system can synchronize the operation of the
light source 134,
the motor 114, the wavefront sampling aperture 118 if it is active also, and
the position
sensing detector 122 to enable lock-in detection. Therefore, the signal to
noise ratio can be
boosted up and DC or low frequency background light generated noise can be
filtered out.
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100431 However, as wavefront shifting is done by a beam scanner at the
optical
Fourier transform plane of a 4-f optical wavefront relay system, when the
refractive error
diopter value of a patient eye is large, the dimension of the object beam at
the Fourier
transform plane will also be relatively large. This means that to cover a
large diopter range,
the beam scanner requires a relatively large beam interception area. In the
case of cataract
surgery, where the working distance between the eye and the input port is
large, the required
beam scanner size would not be practical in terms of cost and commercial
availability.
100441 Fig. 2 shows another optical configuration as disclosed in co-
assigned US
patent application US20120026466 that uses two cascaded 4-f relays having
first and second
Fourier transform planes, A and C respectively, and first and second image
planes, B and D
respectively. Owing to the use of two cascaded 4-f wavefront relays or an 8-f
wavefront relay,
sequential transverse wavefront shifting can be achieved by angularly scanning
the wavefront
beam at or around the second Fourier transform plane C where the wavefront
beam width
(over a desired large refractive error diopter measurement range) can be
maintained within a
certain physical dimension range so that the object beam can be completely
intercepted by a
relatively small beam scanner 212.
100451 As shown in Fig. 2, after the first wavefront relay at the
wavefront image
plane B, the object beam width is reduced because of the difference in the
focal length of the
first lens 204 and the second lens 216, although the beam divergence or
convergence is
increased. The second 4-f wavefront relay comprises a third lens 240 and a
fourth lens 242,
each having a relatively large focusing power or short focal length and a
relatively large
numerical aperture (NA) or beam acceptance cone angle. The beam width at the
second
Fourier transform plane C is now relatively small. By angularly scanning the
beam at the
second Fourier transform plane C, the wavefront image at the second wavefront
image plane
D can be transversely shifted. The transversely shifted wavefront can be
sampled at the
second wavefront image plane D by a wavefront sampling aperture 218 and
focused by a sub-
wavefront focusing lens 220 onto a position sensing device/detector (PSI))
222.
100461 Similarly to the embodiment depicted in Fig. 1, by controlling
the beam
scanner 212 at the second Fourier transform plane C and timing the pulsing of
the light
source, any portion of the wavefront can be sampled. Again, the electronic
control and
detection system can synchronize the operation of the light source 234, the
scanner 212, the
aperture 218 ( if it is a variable aperture) and the PSD 222 to enable lock-in
detection to boost
up the signal to noise ratio and to filter out the noise generated by DC or
low frequency
background light.
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100471 An electronic control system 236 having a user control
interface 238 is
coupled to beam scanner 212 and variable aperture to allow control of these
elements to vary
the scanning pattern or aperture size. In other embodiments the electronic
control system 236
may be coupled to other controllable elements as will be described more fully
below. The
user interface 238 may be in the form of buttons on the instrument, a
graphical user interface
(GUI) on the instrument or on a computer coupled to the electronic control
system 236.
100481 Note that in Figs. 1 and 2, there is only one wavefront
sampling element and
only one position sensing device, and wavefront sampling is conducted in a
pure sequential
manner. In this case only one portion of the entire wavefront is sampled and
therefore optical
energy returned from the eye is not efficiently used.
100491 Fig. 3a shows an example where a beam of light from a light
source 334 (such
as a SuperLuminescent Diode or SLD) operating in pulse and/or burst mode is
launched via a
beam directing element 306 (such as a Polarization Beam Splitter (PBS)) into a
patient eye to
form a relatively small image spot on the retina for the generation of a
wavefront that returns
from the eye. The beam directing element 306 should have a large enough light
beam
interception size to ensure that the object beam carrying the wavefront
information from the
eye over a desired eye diopter measurement range is fully intercepted without
being disturbed
by the edge of the beam directing element.
100501 Using a PBS can help the suppression of interference from light
reflected or
scattered from other undesired optical interfaces of the eye such as the
cornea and the eye
lens. This is because the relatively narrow input SLD light beam is linearly
polarized in a first
polarization direction and light reflected or scattered from the cornea and
the eye lens is also
mostly linearly polarized in the first polarization direction whereas the
retina scattered light
has a large component that is polarized orthogonal to the first polarization
direction. So the
PBS, as the beam directing element 306, serves as both a polarizer for the SLD
beam
propagating towards the eye and also as an analyzer to pass only the object
beam returned
from the retina in a second orthogonal polarization direction.
100511 In addition to the need to filter out a certain polarization
component, the
wavefront leaving the eye also needs to be relayed to a wavefront sampling
image plane. In
Fig. 3a, this is achieved with a 4-f wavefront relay optical configuration
comprising a first
lens 304 and a second lens 316. At the wavefront image plane B, an array of
sub-wavefront
sampling elements comprising, for example an annular array of sub-wavefront
sampling
apertures 318 and a corresponding annular array of sub-wavefront focusing
lenses 320,
sample and focus in parallel a number of portions of the relayed wavefront at
wavefront
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image plane B. A corresponding array of position sensing devices/detectors
(PSDs) 322 (such
as an annular array of lateral effect position sensing detectors or quadrant
detectors) are
arranged behind the array of sub-wavefront sampling elements for detecting the
image spot
centroid position of each sampled sub-wavefront
100521 In order to show the details of the sub-wavefront sampling elements
and the
position sensing devices/detectors (PSDs), we have included in Fig. 3a, a
zoomed-in inset of
the wavefront sampling and centroid detection stage optical elements, with the
annular array
of sub-wavefront sampling apertures 318 deliberately separated from the
annular array of
sub-wavefront focusing lenses 320 although in practice, they are more likely
to be in contact
or close proximity from each other. In the zoomed-in drawing, the annular
array of PSDs 322
are arranged around the back focal plane of the sub-wavefront focusing lenses
320 to result in
a relatively sharp focused image spot on the PSDs when the wavefront is
planer, however,
this does not have to be the case as the annular array of PSDs 322 can be
arranged before or
after the focal plane of the sub-wavefront focusing lenses 320. In the example
embodiment,
by sampling around an annular ring of the wavefront from an eye, the sphere
and cylinder
refractive error of the eye and the axis of the cylinder can be determined.
However, the
pattern of the parallel sub-wavefront sampling elements can be in other forms
such as a spoke
pattern or a two-dimensional linear array form.
100531 Fig. 3a depicts a lock-in amplifier 343, coupled to receive the
output signals
from the array of PSDs 322, for noise suppression. A display 345 may be
coupled to the
electronics system 336 that receives the output of the lock-in amplifier 343.
The operation of
the lock-in amplifier 343 is described below with reference to Fig. 4. The
electronics system
336 has processing capabilities to process the output of the lock-in amplifier
343 including
applying algorithms to determine refraction, aberrations and other diagnostic
or clinical
factors. The display 345 could be implemented as a heads-up display in
association with a
surgical microscope or a large screen display or a back projection display or
as part of a
personal computer or workstation.
100541 Note that as compared to prior art wavefront sensor systems,
the presently
described example embodiment has a number of features that when combined in
one way or
another make it advantageous for eye refractive surgery. Firstly, the sub-
wavefront sampling
elements are physically separated so that the density is generally less than
the density of a
standard lenslet array used in a typical Shack-Hartmann wavefront sensor. This
is achieved
by making the lenslet-to-lenslet distance or lenslet pitch larger or by making
the diameter of
each lenslet larger than that of a lenslet used in a typical Shack-Hartmann
wavefront sensor.
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Alternatively, the focal length of the lenslets of the lenslet array can be
made shorter than the
focal lengths of lenslets used in a typical Shack-Hartmann wavefront sensor.
As a result, a
sufficiently large diopter measurement range can be covered without cross
talk, i.e. the
landing of a sampled sub-wavefront image spot onto a non-corresponding PSD.
100551 In order to illustrate the point. Fig. 3b shows a lenslet array of a
typical Shack-
Hartmann wavefront sensor with a corresponding array of position sensing
devices/detectors
and what happens to the maximum diopter measurement range without cross talk.
In the
present description, the term "cross talk" refers to a condition where a
portion of or an entire
light beam intended to be focused by a lenslet on a corresponding detector is
focused on a
neighboring detector.
100561 The lenslet array 342 of a typical Shack-Hartmann wavefront
sensor is densely
packed with the lenslets arranged next to each other without any gap. In this
case, there are a
large number of lenslets per unit area and the sampling density for measuring
a wavefront is
high. Assuming that the wavefront to be measured is a spherical convergent
wavefront 344 as
shown, then the maximum average sub-wavefront tilt, Om, that can be measured
without cross
talk will be limited by the radius r and the focal length f of each lenslet
where Om = tan [HA.
Fig. 2 illustrates that the curvature of the wavefront increases for large
positive or negative
diopter values. Therefore Om indicates the maximum diopter measurement range
value.
100571 In Fig. 3b, there is an angular spread of the sub-wavefront
tilt angle and the
sub-wavefront sampled by the far left lenslet will be focused by this far left
lenslet to form a
light spot that lands at the right border of PSD I between PSD1 and PSD2. As
can be seen,
any further increase in the convergence or the absolute diopter value of the
convergent
spherical wavefront will cause the tilt angle to exceed Om and cause the light
spot sampled by
the far left lenslet to land beyond the border between PSD I and PSD2 into
PSD2, thereby
causing cross talk. In fact, since the sampled sub-wavefront is convergent,
the focused spot is
actually in front of the focal plane 346, and accordingly the corresponding
image spot on the
focal plane 346 will be wider rather than that in sharp focus, so the sub-
wavefront tilt
measurement range is slightly less than Om. A similar situation exists for the
far right lenslet
and the two position sensing devices/detectors PSD8 and PSD7.
100581 On the other hand, if the wavefront is a spherical divergent
wavefront, the
sharply focused image spots will, in general, actually be behind the focal
plane 346, so the
light spot on the focal plane 346 will also be wider rather than that in sharp
focus, and
accordingly the sub-wavefront tilt measurement range will again be slightly
less than 13.. If
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the wavefront is not spherical but has prismatic tilt and/or astigmatism
and/or even other high
order aberrations, a local sub-wavefront tilt sampled by any of the lenslets
can exceed the tilt
angle measurement range limit Om.
100591 However, if the parallel sub-wavefront sampling elements are
not closely
packed but are intelligently distributed with the center-to-center distance
between two
elements properly controlled, then it is possible to deliberately avoid cross
talk and also
achieve a certain desired large enough diopter measurement range.
100601 Fig. 3c shows an example embodiment of an arrangement of the
sub-
wavefront sampling elements with a corresponding array of position sensing
devices/detectors and illustrates that the maximum diopter measurement range
without cross
talk can be increased. In the illustrated example, each sub-wavefront sampling
element
comprises a lenslet 352 and an aperture 359 in front of the corresponding
lenslet. In other
words, a patterned aperture array mask 358 is combined with a corresponding
lenslet array
352 to act as an array of parallel sub-wavefront sampling elements. Assuming
that the focal
length of each lenslet is the same as that shown in Fig. 3b and is represented
by the same f,
whereas now the distance from the center of one lenslet to the border or mid-
point between
two sub-wavefront sampling elements is d as shown, then the maximum average
sub-
wavefront tilt that can be measured without cross talk will now be 13. = tan-1
[dill Since d is
greater than r, the local sub-wavefront tilt measurement range is thus
increased. In fact, Fig.
3c shows a more convergent spherical wavefront 354 that is being sampled than
the
wavefront depicted in Fig. 3b with the limitation imposed byilm = tan -1W.
Clearly, the
absolute diopter value of the convergent spherical wavefront 354 in Fig. 3c
that can be
sampled without cross talk is higher than that of the wavefront 344 of Fig.
3b.
100611 In Fig. 3c the widths of the PSDs are increased as compared to
the width of
the PSDs in Fig. 3b, i.e., d is greater than r. The use of wider PSDs instead
of narrow PSDs
with spaces between them larger is to ensure that with an increase in the sub-
wavefront tilt
the light spot landing on a corresponding PSD can be captured by the
corresponding PSD.
Otherwise, if the PSD has the same smaller size as that shown in Fig. 3b but
were spaced
apart, then an increase in the sub-wavefront tilt could cause the sub-
wavefront light spot land
in the space between the photo-sensitive area of the PSDs. In other words, the
light spot
would not be captured by the PSD to produce an electrical signal.
100621 Also in Fig. 3c the lenslets have larger diameter compared to
the diameter of
the lenslets in Fig. 3b but have the same focal length. Designing a larger
lenslet with the
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same focal length has the advantage that when such a lenslet is combined with
a variable
aperture, varying the size of the aperture can provide flexibility in
controlling the size of the
sub-wavefront to be sampled over a larger sampling size range. For example,
for refractive
error measurement which only involves the determination of the sphere and
cylinder diopter
values and the cylinder axis, a larger sub-wavefront sampling size can provide
the benefit of
averaging as well as reducing the burden of data processing. In other words,
the high spatial
wavefront sampling density as would normally be provided by a standard Shack-
Hartmann
wavefront sensor can be an over-kill for that type of refractive measurement
and can
substantially increase the data capturing, transferring and processing time,
thus slowing down
the operation of the wavefront sensor and making it too slow for real time
refractive surgical
procedure applications.
100631 On the other hand, if only a small area of a cornea needs to be
operated on
using for example, a LAS1K system, the laser ablation spot size on the cornea
is generally
much smaller than the size of a typical lenslet of a Shack-Hartmann wavefront
sensor. In such
a case, the aperture depicted in Fig. 3c can be made correspondingly small
enough and
wavefront scanning as will be discussed below can be employed to allow non-
averaged
wavefront sensing over a small cornea area so that very high measurement
precision can be
achieved in terms of high order wavefront aberration measurement. In fact, in
some example
embodiments the aperture array is made active in the sense that the aperture
size can be
actively controlled. It should be noted that the patterned aperture array can
also be arranged
after the patterned lenslet array and may not be absolutely required as their
function can be
served by the diameter of the lenslet.
100641 Further, in view of the formula for calculating Om it is seen
that the sub-
wavefront tilt measurement range without cross talk, Om, can also be increased
by choosing a
smaller focal length valuef. In such a case, the size of each PSD can be
smaller to still
provide the sub-wavefront tilt measurement range. However, the tilt
measurement sensitivity
will also suffer because for the same amount of change in the sub-wavefront
tilt there will be
a smaller displacement of the light spot on the PSD as is well known to those
skilled in the art.
100651 In order to provide even more flexibility, some example
embodiments use a
lenslet array having variable focal length or a lenslet array with certain sub-
groups of the
lenslet array having different focal lengths. The longer focal length sub-
group of lenslets can
provide better sensitivity while the shorter focal length sub-group of
lenslets can provide
larger sub-wavefront tilt measurement dynamic range. There can be two or three
or more sub-
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groups of lenslets and accordingly two or three or more sets of position
sensing detectors
arranged at different distances from the lenslets.
100661 A significant problem with existing wavefront sensors used in
vision
correction procedures is detecting the wavefront returned from the eye in the
presence of
background optical or electronic noise. Examples of problematic background
noise
components are ambient light incident on the detector and lif noise generated
by the detector
itself, and other radiated or conducted electronic noises. Both of these
background noise
components have significant amplitudes at the frame rate of standard two
dimensional
CCD/CMOS image sensors.
100671 In some of the example embodiments the light source used for
creating the
object wavefront from the eye is operated in pulse andlor burst mode. The
pulse repetition
rate or frequency is higher than the typical frame rate of a standard two
dimensional
CCD/CMOS image sensor. For example, the pulse rate of the light source in this
example
embodiment can be in or above the kHz range. For a CCD/CMOS image sensor the
frame
rate is typically about 25 to 30 frames per second. The PSDs of the present
disclosure are
two-dimensional position sensing devices/detectors (PSDs), all with
sufficiently high
temporal frequency response so that they can be operated in lock-in detection
mode in
synchronization with the pulsed light source at a frequency above the 1/f
noise frequency
range. The electronic control and detection system is coupled to at least the
light source and
the array of PSDs and is configured to phase lock the operation of the light
source and the
parallel PSDs. The electronic control and detection system can also be coupled
to an array of
variable sub-wavefront sampling apertures to further control the sampling
aperture size if the
sampling apertures are active.
100681 Fig. 4 is a block diagram showing one example embodiment of a
lock-in
detection amplifier 400. Note that phase sensitive lock-in detection is a
powerful synchronous
detection technique well known to those skilled in the art for the recovery of
small signals
which can be obscured by noise much larger than the signal of interest. A
mixer 496 has a
first input coupled to the output of a preamplifier 495 having a signal from
the PSD A.C.-
coupled to its input. The mixer 496 has a second input coupled to the output
of a phase-
locked loop 497 which is locked to the reference signal that drives and pulses
the SID. The
input signals are mixed (multiplied) by the mixer 496 to form a mixer output
signal. The
output of the mixer 496 is passed through a low-pass filter 498 and amplified
by an output
amplifier 499 to form the output of the lock-in detection amplifier 400.
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100691 The operation of the lock-in detection amplifier will now be
described. The
input signal from the PSD to the preamplifier 495 includes a component at the
reference
frequency which indicates the deflection of the sub-wavefront measured by the
position-
sensor detector. The amplitude of this component is the desired output of the
lock-in
detection amplifier. The input signal from the PSD also includes noise signals
at low
frequency such as the frequency of the ambient light and 1/f noise from the
detector.
100701 The input to the phase-locked loop (PLL) is a signal having
substantial
amplitude only at the reference frequency.
100711 The amplitudes of input signals to the mixer are multiplied.
Each frequency
component of the amplified PSD signal is converted into a first mixer output
component at a
frequency equal to the sum of the frequency of a PSD frequency component and
the reference
frequency and a second mixer output component at a frequency equal to the
difference of the
frequency of the PSD frequency component and the reference frequency.
100721 The low-pass filter 498 passes signals having a frequency near
zero (a D.C.
signal) and blocks signals having frequencies greater than those near zero
(A.C. signals). All
noise components at frequencies other than the reference frequency are blocked
because both
the sum and the difference of the noise frequency and the reference signal are
not equal to
zero so both mixer output components are A.C. signals and are blocked by the
low-pass filter.
100731 The frequency of the first mixer output signal for the
frequency component of
the PSD signal at the reference frequency is equal to the sum of the reference
frequency with
itself which is twice the reference frequency and thus is an A.C. signal that
is blocked by the
low-pass filter. However, the frequency of the second mixer output signal for
the frequency
component of the PSD at the reference frequency is equal to the difference of
the reference
frequency and itself which is zero. This is a D.C. signal that is passed by
the low-pass filter.
100741 Accordingly, the output of the lock-in amplifier is a measure of
only the
frequency component of the PSD signal at the reference frequency. All noise
signals at
different frequencies are blocked by the low pass-filter. The low-pass
filtered signal can be
further amplified by another amplifier 499 for analog to digital (A/D)
conversion further
down the signal path.
100751 It should be noted that each PSD can have more than one
photosensitive area
(for example 4 as in the case of a quadrant detector) corresponding to more
than one
photodiodes or photo-detectors. When implementing parallel lock-in detection
the number of
channels needed is the number of parallel PSDs times the number of photo-
detection signal
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lines of each PSD. With parallel sampling, we can simultaneously collect a
number of sub-
wavefront samples across the wavefront.
100761 Not shown in Fig. 4 is the AID converter and the rest of the
electronic
detection and control module. Activating the AID converter at the same
frequency as the
signal pulsing the SLID can also allow the collection of both dark and light
samples before
and during the SW pulse to further remove the effects of electromagnetic
interference as
well as ambient light from the room or the microscope on which the device may
be mounted.
100771 Note that prior art wavefront sensors generally do not operate
the light source
in pulse and/or burst mode (at least at a frequency range above the 1/f noise
region, i.e.
around and beyond the kHz range) because either the light source for wavefront
sensors used
in astronomy, such as a distant star in space, is beyond control (see for
example, US6784408)
or there is no advantage of operating the light source in pulse or burst mode
because a typical
CCD/CMOS image sensor does not have a high enough frame rate to be operated in
the
above 1/f noise frequency range.
100781 A Hartmann-Shack wavefront sensor can be operated by selectively
blocking
some of the lenslets of the Hartmann-Shack lenslet array (see for example,
US7414712) to
cover a large diopter measurement range. However, this approach is expensive
and still
suffers from the same limitation that the image sensor used is scanned at a
low frame rate.
100791 In the present described example embodiments, the sub-wavefront
sampling
elements are preferably physically separated from each other at the wavefront
image plane B
as shown by the zoomed-in inset in Fig. 3a. Note that in the example
embodiment of Fig. 3a,
each sub-wavefront sampling element comprises an aperture and a focusing
lenslet. However,
the focusing lenslet can either be directly used to function as an aperture or
can even be
removed. In the latter case, the sampled sub-wavefront beam will not be
focused but will still
land as a light spot on a corresponding PSD with a different centroid position
for a different
sub-wavefront tilt although the aperture size needs to be generally smaller
than the PSD size
in order to avoid cross talk.
100801 Also in order to separately show the array of sub-wavefront
sampling
apertures and the array of sub-wavefront focusing lenses, the inset drawing of
Fig. 3a has
deliberately separated the two from each other. In practice, it is more likely
that they will be
arranged in close proximity. The large diopter measurement range is ensured by
physically
designing the spacing of the sub-wavefront sampling elements such that within
the designed
large diopter coverage range the tilt of any sampled sub-wavefront will not be
focused to land
on its neighboring PSD.
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100811 In example embodiments, higher energy efficiency can be
achieved while, at
the same time, the 1/f noise can be substantially reduced thereby allowing DC
or low
frequency background noise such as noise generated by the illumination light
of a surgical
microscope to be effectively filtered out.
100821 These features make the presently described example wavefront
sensor, when
integrated with or attached to an ophthalmic surgical microscope, extremely
suitable for a
vision correction surgical procedure such as cataract surgery. A. cataract
surgeon can perform
the surgery without stopping half way to turn off the illumination light of
the surgical
microscope and waiting for the capture of multi-frames of data and for the
processing of the
data in order to obtain a refraction measurement.
100831 With the present example embodiments, the diopter measurement
dynamic
range can be made large enough (for example, up to -301)) for the refractive
state of even an
aphaldc eye to be fully covered. Furthermore, by sampling just a properly
selected number of
sub-wavefronts around an annular ring of the wavefront from a patient eye, one
can obtain
the sphere and cylinder diopter values as well as the cylinder axis as needed
for the selection
of an intra-ocular lens (IOW and for the confirmation of, for example,
emmetropia or an
intended sphero diopter value of a pseudo-phakic eye. By properly selecting
the wavefront
sampling number around each annular array, the required data transfer rate and
data
processing resources can be substantially reduced.
100841 Example embodiments will now be described that provide more spatial
sampling points and/or higher spatial resolution as can normally be provided
by prior art
ophthalmic wavefront sensors, although this may not be absolutely needed for a
cataract
surgery. These embodiments can also measure higher order aberrations as well
as to possibly
provide a two dimensional wavefront map. These example embodiments include an
angular
light beam scanner 312 (such as a transmissive electro-optic or magneto-optic
beam
deflector) that can be arranged at the Fourier transform plane A of the 4-f
relay as shown in
Fig. 3a to transversely shift or scan the wavefront at the wavefront image
plane B relative to
the array of sub-wavefront sampling elements. In doing so, one can achieve sub-
aperture
spatial resolution as has been disclosed in US6376819 and also sample those
portions of the
relayed wavefront between the sampling apertures if the relayed wavefront is
otherwise static.
100851 Fig. 5 shows one example of sequential transverse wavefront
shifting or
scanning as applied to the optical configuration of Fig. 3a. In this example,
8 sub-wavefront
sampling lenslets 501 are arranged in the form of an annular array at the
wavefront image
plane B with sufficient spacing between any two neighboring lenslets such that
there is no
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cross talk over the intended refractive diopter measurement range. The relayed
wavefront is
shown as a circular disk 502 with the 8 lenslets 501 sampling 8 portions of
the relayed
wavefront. Without any wavefront shifting or scanning, the 8 sampled sub-
wavefronts are
rotationally symmetric with respect to the wavefront image 502.
100861 The circles 502-520 represent a first portion of a relayed wavefront
that is
incident on the array of lenslets. The location of the circle, i.e., the first
portion of the
wavefront, is scanned to different positions as shown in the various drawings
that allow sub-
portions of the first portion to be sampled.
[00871 Of the 4 rows shown on the right part of Fig. 5, the top two
rows (503 to 510)
show one example of the effect of sequentially transversely shifting the
relayed wavefront
relative to the 8 lenslets. From 503 to 510, the relayed wavefront is shown to
have been
sequentially shifted by the same distance respectively to the right, the right-
bottom, the
bottom, the bottom-left, the left, the left-top, the top, and the top-right
directions.
100881 The bottom two rows (513 to 520) show the equivalent result of
moving the
lenslet array relative to the wavefront instead of moving the wavefront
relative to the lenslet
array. The 8 dotted line circles in each case from 513 to 520 show the
original sampling
position of the 8 lenslets with respect to the non-shifted first portion of
the relayed wavefront.
From 513 to 520, the 8 solid line circles show the equivalent relative
movement of the 8
lenslets with respect to the original lenslet positions if the first portion
of the relayed
wavefront is treated as stationary. The total sampling pattern 512 resulting
from the shifting
depicted in the top two rows shows the cumulative sampling effect.
100891 From the total sampling pattern 512, it can be seen that
without wavefront
shifting only the original 8 annular array sub-portions of wavefront will be
sampled and that
with wavefront shifting other sub-portions of the wavefront can be sampled.
100901 In the illustrated example, sampling overlaps are shown as can be
seen in the
total sampling pattern 512. This indicates that spatial sampling resolution
smaller than the
sampling aperture size (which in this illustrated example is the lenslet
diameter) can be
achieved. In fact, one can control the scanning angle of the scanner 312 to
achieve any
desired spatial sampling resolution as long as the beam scanner can be
controlled to whatever
desired practically achievable angular precision. In addition, the total
sampling pattern 512
also shows that as a result of transversely shifting the relayed wavefront,
not only can
portions of the non-shifted wavefront between any two neighboring lenslets be
sampled, but
also that portions of the wavefront towards the center and away from the
center of the non-
shifted wavefront can also be sampled. In the total sampling pattern 512 it
can already be
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seen that, if needed, three annular rings can be sampled. Any portion of the
wavefront can be
sampled by controlling the beam shifter 312.
100911 it should be noted that the array of the sub-wavefront sampling
elements do
not need to be in the form of an annular array as illustrated in Fig. 3a. For
example, they can
be in the form of a rectangular array as long as they are physically well
separated from each
other to ensure that a large enough refractive error diopter measurement
dynamic range can
be covered without cross talk. Alternatively, they can be more closely spaced
as long as the
focal length of the lenslet behind each sub-wavefront sampling aperture is
correspondingly
shorter and the distance between the lenslets and the PSDs is correspondingly
reduced. It
should also be noted that the number of lenslets does not need to be
restricted to 8 and can be
any number arranged in any form.
100921 As discussed before in comparing the configuration of Fig. 1 to
that of Fig. 2,
if scanning is to be implemented with a 4-f relay then the beam scanner 312
will need to have
a large beam interception window size. To overcome this limitation and also
provide other
various improvements, Fig. 6 shows another example embodiment. As can be seen
from Fig.
6, the optical configuration is, in some aspects, similar to that shown in
Fig. 2. However,
there are a number of new features that can be implemented either individually
or in
combination with others.
100931 In the example embodiment of Fig. 6 a relatively narrow beam of
light from a
light source 634 (such as a superluminescent diode (SLD)) operating in pulse
and/or burst
mode is launched through a focus adjustable lens 637 and directed by a beam
directing
element 606 (such as a polarization beam splitter or PBS) to a patient's eye
for generating a
wavefront returned from the eye. The focusing change from the lens 637 can be
utilized to
ensure that the spot size of the light beam when landing on the retina is
relatively small for
various refractive states of the eye. In addition, a scan mirror 680 for
scanning the SLD beam
can be arranged at a back focal length distance of the first lens 604 so that
the SLD beam
scanner position is conjugate to the retina of an emmetropic eye. In this way,
an angular scan
of the SLD beam scanner 680 will cause a transverse scan of the SLD beam with
respect to
the cornea plane but still allow the SLD beam to land on the same retina
location if the eye is
emmetropic. This scanner can be used to scan the SLD beam to follow any eye
movement so
that SLD beam can always enter the eye from the same cornea location.
100941 Instead of using a 4-f wavefront relay as shown in Fig. 3a, an
8-f wavefront
relay system comprising a first lens 604, a second lens 616, a third lens 640
and a forth lens
642 is used to relay the wavefront from the pupil or cornea plane through an
intermediate
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wavefront image plane B to a final wavefront image sampling plane D. Such an 8-
f wavefront
relay can be considered as comprising two cascaded 4-f relays. The first relay
includes the
first and second lenses that guide the wavefront relay beam through a Fourier
transform plane
A to the intermediate wavefront image plane B. The second relay includes the
third and
fourth lenses that further relay the wavefront from the intermediate wavefront
image plane B
through a Fourier transform plane C to the final wavefront image plane D. The
benefit of
such an 8-f wavefront relay optical configuration has been discussed with
reference to Fig. 2
and more details can be found from co-assigned patent application
US20120026466.
100951 Instead of using only one sub-wavefront sampling element and
one PSD as
shown in Fig. 2, an. array of sub-wavefront sampling elements comprising, for
example, a
rectangular array of apertures 618 and a corresponding rectangular array of
sub-wavefront
focusing lenslets 620, can be disposed substantially at the final wavefront
image plane D to
sample and focus a desired array of sub-wavefronts. Again, the sub-wavefront
sampling
elements can be physically separated from each other and/or the focal length
of the lenslet
array can be properly selected in such a way that a large refractive error
diopter measurement
range can be covered without cross talk.
100961 These elements can be combined with a corresponding array of
parallel PSDs
to detect the image spot centroid positions of the sampled array of sub-
wavefronts, and to
achieve parallel wavefront sampling with lock-in detection by synchronizing
the detectors
with the pulsed light source.
100971 As an alternative to directly arranging the PSDs substantially
at the back focal
plane of the lenslets behind the sub-wavefront sampling elements, a lens 621
can be used to
relay and also preferably optically magnify the virtual image spots formed at
a virtual image
spot plane 622a, as shown in the inset of Fig. 6, to a new plane of real PSDs
622 as is well
known to those skilled in the art (see for example US6595642).
100981 This lens 621 is especially useful if a relatively high density
lenslet array with
a shorter focal length is used to cover a desired large diopter range.
Typically, such a lenslet
array has a relatively small pitch, i.e., the spacing between the centers of
the lenslets in that
array, of, for example 0.5 mm to 1.0mm, whereas each PSD can be relatively
large (for
example, in the case of a quadrant detector, about 5 mm in diameter).
Therefore, to achieve a
one-to-one correspondence, the image spots formed by the lenslet array can be
optically
magnified and relayed by the lens 621 to a larger pitch array to increase the
distance between
two neighboring PSDs so that the PSDs can be arranged to physically fit on a
substrate.
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100991 As in the case of Fig. 2, a small size beam scanner or
deflector 612 can be
arranged at the second Fourier transfoim plane C to fully intercept and
angularly scan the
whole object beam that carries the eye wavefront information over a desired
large refractive
error diopter range. However, compared to Fig. 2, the needed beam angular scan
or deflection
range can now be substantially lessened. This is because with the use of an
array of sub-
wavefront sampling elements, one only needs to scan the object beam within an
angle range
such that the transverse wavefront shift at the final wavefront image plane D
equals the pitch,
i.e., distance between the centers of adjacent PSDs in the sub-wavefront
sampling element
array in both the x and y directions. In this way, all the wavefront portions
incident between
any two sub-wavefront sampling elements can be sampled if the relayed
wavefront is
otherwise not scanned. This will allow different types of beam scanners to be
used in addition
to a reflective MEMS scanner, such as, for example, a transmissive electro-
optic or electro-
magnetic scanner that generally can only cover a relatively small angular
scanning range.
1001001 Similar to the case of Fig. 3a, a lock-in amplifier 643 can be
coupled to
receive the output signals from the array of PSDs 622 for noise suppression. A
display 645
may be coupled to the electronics system 636 that receives the output of the
lock-in amplifier
643. The electronics system 636 has processing capabilities to process the
output of the lock-
in amplifier 643 including applying algorithms to determine refraction,
aberrations and other
diagnostic or clinical factors. The display 645 could be implemented as a
heads-up display in
association with a surgical microscope or a large screen display or a back-
projection display
or as part of a personal computer or workstation.
1001011 Fig. 7 shows one example of sequential transverse wavefront
shifting or
scanning as applied to the optical configuration of Fig. 6. In this example,
21 sub-wavefront
sampling lenslets 701 are arranged in the format of a two dimensional linear
array at the
wavefront image plane D with sufficient spacing between any two neighboring
lenslets such
that there is no cross talk over the intended refractive error diopter
measurement range. As in
Fig. 5, the first portion of the relayed wavefront is shown as a circular disk
702 incident on
the lenslet array with the 21 lenslets 701 sampling 21 sub-portions of the
first portion relayed
wavefront. Without any wavefront shifting or scanning, the 21 sampled sub-
portions of the
first portion of the relayed wavefronts are regularly distributed in a two
dimensional array
format with respect to the relayed wavefront 702.
1001021 Of the 4 rows shown in Fig. 7, the top two rows (703 to 710)
show one
example of what happens when the relayed wavefront is sequentially
transversely shifted
relative to the 21 lenslets. From 703 to 710, the first portion of the relayed
wavefront is
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shown to have been sequentially shifted by the same distance in either the
horizontal and/or
the vertical direction, respectively to the right, the right-bottom, the
bottom, the bottom-left,
the left, the left-top, the top, and the top-right directions.
1001031 The bottom two rows (713 to 720) show the equivalent result of
moving the
lenslet array relative to the wavefront instead of moving the wavefront
relative to the lenslet
array. The 21 dotted line circles arranged in a two dimensional linear array
format in each
case from 713 to 720 show the original sampling position of the 21 lenslets
with respect to
the non-shifted first portion of the relayed wavefront. From 713 to 720, the
21 solid line
circles show the equivalent relative movement of the 21 lenslets with respect
to the original
lenslet positions when the first portion of the relayed wavefront is treated
as stationary. The
total sampling pattern 712 shows the cumulative sampling effect. From the
total sampling
pattern 712, it can be seen that without wavefront shifting the original 21
lenslet portions of
the relayed wavefront will be sampled and with wavefront shifting, regions
around the
original 21 lenslets can be sampled.
1001041 In fact, the illustrated example shows a transverse shift in either
the horizontal
and/or the vertical direction by a distance equal to the diameter of each
lenslet and the
original pitch or spacing between two horizontal or vertical lenslets is made
equal to three
times the diameter of each lenslet. In other words, the gap distance is equal
to twice the
diameter of each lenslet. As a result, the illustrated scanning enables one to
achieve sampling
of the relayed wavefront as if the wavefront has been sampled by a closely
packed two
dimensional linear lenslet array as in the case of a typical Hartmann-Shack
wavefront sensor.
1001051 It should be noted that one can control the scanning angle of
the beam scanner
612 and the pulsing of the SI,D to realize sampling at smaller transverse
wavefront shift
distances and hence to achieve any desired spatial sampling resolution. In
addition, the
illustrated example also shows that with the use of a two dimensional linear
array of sub-
wavefront sampling elements the beam scanner 612 needs only to scan a small
angle range in
the horizontal and vertical directions in order to allow all portions of the
relayed wavefront to
be sampled.
1001061 Note that the array of wavefront sampling apertures and/or PSDs
can also be
made active. The aperture size for sampling the sub-wavefronts can be
dynamically adjusted
utilizing, for example variable diaphragm arrays or a liquid crystal based
aperture size
variable array. The apertures can also be active in the sense that different
portions of the
relayed wavefront image can be directed to different PSDs using a MEMS mirror
array as
disclosed in US6880933. The focal length of the sub-wavefront focusing lens
can also be
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varied using, for example, include liquid crystal microlens arrays and
flexible membrane
based liquid lens arrays. In addition, the position of the PSDs or the
position of the sub-
wavefront focusing lenslet array can also be longitudinally moved.
1001071 In the example embodiments of both Fig. 3a and Fig. 6, there is
an electronic
system that is coupled to at least the light source and the PSDs to phase-lock
the operation of
the light source and the PSDs at a frequency above the 1/f noise frequency
range so that DC
or low frequency background noises can be substantially filtered out. In
addition, the
electronic system can also be coupled to the focus variable lens 637 for
controlling the focus
of the SLD beam, to the SLD beam scanner 680, to the wavefront object beam
scanner/deflector 612, to the aperture array 618, to the lenslet array 620,
and to the lens 621.
These electronic couplings are meant to control the operation of the coupled
elements or
devices.
1001081 Further, although in Fig. 3a and 6 the SLD beam is launched
from behind the
first lens, the SLD beam can be launched from anywhere between the eye and the
final
wavefront image plane D (such as in front of the first lens or even behind the
second lens)
and its beam divergence or convergence can also be adjusted by other means in
addition to
the focus variable lens 637 (such as using an axially movable lens) to ensure
that a desired
light spot is formed on the retina of various eyes.
1001091 The pulsing of the light source is to be interpreted as
encompassing all kinds
of temporal modulation of the light source. For example, the SLD can be
modulated between
on/off or dark/bright states; it can also be modulated between a first light
level state and a
second light level state; the SLD can also be modulated in a sinusoidal
manner. Another
example is to have the light source operated in a burst mode to create a
stream of light pulses,
in which each pulse is also modulated by a carrier or modulation frequency.
Accordingly,
lock-in detection or synchronized detection should be interpreted as any phase
locking or
coherent detection means. The lock-in detection can be at both the high
carrier frequency
and/or at the pulse repetition rate/frequency.
1001101 The optical path for launching the SLD beam and also for
guiding the returned
object beam can be folded in various ways to save space and make the wavefront
sensor
module compact. This means that there can be mirrors or other optical beam
folding elements
used to fold the various optical paths. The beam scanner can be either
transmissive or
reflective. In addition to a 1:1 ratio wavefront relay, there can be optical
magnification or
demagnification of the wavefront from the eye to the intermediate wavefront
image plane and
to the final wavefront sampling image plane. This means that the focal length
of all the lenses
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being used for relaying the wavefront can be of different values. In addition
to two cascaded
4-f wavefront relays, there can be more cascaded 4-f or other wavefront
relays.
1001111 Due to the fact that the intermediate wavefront image plane B
of Fig. 6 is
conjugate to the object wavefront plane and the final wavefront image plane D,
a wavefront
compensator or defocus offsetting element 689 can be located at plane B and
controlled by
the electronics system. In doing so, the wavefront sensor system can be
converted into an
adaptive optics system for various other applications. In addition to simply
fully
compensating the overall wavefront aberration as is normally done for an
adaptive optics
system, one can also either partially or full compensate only one or some of
the wavefront
aberrations to allow the remaining uncorrected wavefront aberrations to
exhibit themselves
more pronouncedly and hence to be more precisely measured. For example, the
degree of
sphere defocus can be fed back to the compensator or offsetting element 689
that affects the
divergence or convergence of the detected wavefront. This feedback can change
the
measured defocus so it forms a closed-loop system and closed-loop control
techniques may
be used to bring the divergence or convergence of the measured wavefront to
any desired
value, most likely to bring the value near zero so that the wavefront is
substantially planar. In
addition, the information about the sign and degree of defocus can be used to
adjust the
variable focus lens 637 that affects only the divergence or convergence of the
SLD beam to
form an open-loop control system.
1001121 The spatial arrangement of the sub-wavefront sampling elements and
the
associated PSDs do not need to be arranged with a regular constant pitch or in
an annular
array or a rectangular array format but can be in any format. For example,
there can be two or
more annular ring arrays with the outer annular array sub-wavefront sampling
elements
spaced farther apart than those of the inner annular array(s).
1001131 Moreover, the transverse position of the PSDs can also be actively
changed in
response to the refractive state of a patient eye. For example, when the eye
is aphakic, the
wavefront from the eye at the corneal plane is generally relatively highly
divergent and this
wavefront, when relayed to the final wavefront image plane, will also be
highly divergent. In
this case, if an annular ring array of sub-wavefront sampling elements are
used to sample the
relayed wavefront, the corresponding annular array of PSDs can be moved
radially outward
with respect to the annular ring array of sub-wavefront sampling elements so
that, if the
relayed wavefront is a perfect spherically divergent wavefront, the image or
light spot
centroid of each sampled sub-wavefront is at or near the center of each
corresponding PSI).
In this way, any additional wavefront tilt deviation from the imagined perfect
spherically
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divergent wavefront can be detected with high precision as only the central
potion of each
PSD is used for centroid detection. In addition, it should be noted that the
lenslet array 320 or
620 (Figs. 3a and 6) may not be absolutely needed as in the case of a Hartmann
Shack
wavefront sensor versus Hartmann wavefront sensor, because a Hartmann array of
holes will
also work.
1001141 Still further, a spatial light modulator (SLM) can also be
combined with a high
density lenslet array and the SLM can be operated in synchronization with the
light source
and also the PDS array so that only a selected number of apertures are opened
over a selected
number of lenslets during a light source on period. For example, one or more
annular array(s)
of lenslets can be opened and the decision on which annular array is opened
can be made
depending on the sphere or defocus diopter value of the object wavefront.
Accordingly, a
desired annular array of wavefront sample data will be collected. Sampling
around only one
annular array will give only refractive errors but not high order aberrations,
which will be
sufficient for cataract surgery applications. With sequential scanning or the
opening of
different lenslets, high order aberrations can be measured.
1001151 In addition to lateral-effect position sensing detectors and
quadrant
detectors/sensors, other types of PSDs can be used that operate at
sufficiently high frequency
and determine the centroid position of a sampled sub-wavefront image spot. For
example,
each PSD can be a cluster of 3 or more photodiodes. Each PDS of the PSD array
can also be
some clustered pixels of a high speed two dimensional image sensor that has a
high frame
rate, although such an image sensor will likely be expensive. Each PSD of the
PSD array can
also be a CMOS image sensor programmed to only output data from a certain
number of
pixels of a programmed region of interest (ROI) with global shutter exposure
operation.
Currently, a conventional large pixel count image sensor can generally only be
programmed
to output data from one ROI. But this does not mean that there is no
possibility in the future
to simultaneously output multiple ROIs' data at high enough frame rates with
global
exposure control. When this possibility becomes a reality, one can directly
use a single two
dimensional image sensor to allocate a corresponding array of ROIs as if they
are an array of
PSDs operating in lock-in detection mode with high enough temporal frequency
response.
The pulse turn-on time can be synchronized with the camera exposure. In other
words, the
light source can be turned on for a short duration within the time that the
camera is collecting
light. Alternatively, the SLD source can be turned on for a slightly longer
time than the
camera exposure time so that the effective pulse duration is determined by the
camera
exposure time.
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1001161 In addition to standard lock-in detection, double sampling can
also be
employed to further reduce noise. For example, the light source can be
modulated between a
bright state and a dark state. The PSD array can record the signal of the
image spots formed
by focusing sub-wavefronts during the bright state and also record a
background signal
during the dark state. When the background signal is subtracted from the
signal recorded
during the bright state, the result is an improved estimate of the desired
centroid of the image
spots. In one example, a cluster or a number of clusters of pixels of a
CCD/CMOS image
sensor can be programmed as one or more regions of interests (ROIs) at act as
an array of
PSDs and each ROI can be further divided into bright state sub-rows and sub-
columns and
dark state sub-rows and sub-columns. Every other sub-row and sub-column can be
sampled at
every other bright and dark period. In this way, bright and dark sampling can
be achieved by
the same ROI or PSD at a higher frame rate as fewer pixels are used per frame.
One half of
the pixels in each ROI can be synchronized to the pulse "on" of SLD light and
the other half
can be synchronized to the pulse "off" of SLD light.
1001171 Alternatively, the electronic signal from the PSD array can be
sampled at a
frequency ten or more times higher than the light source pulsing frequency,
converted to a
digital signal and then digitally filtered. Once converted to a digital
signal, other digital signal
extraction algorithms such as Kalman filtering can also be employed.
1001181 Still further, in addition to the conventional 4-for 8-f
wavefront relay
configuration shown in Fig. 3a and 6, any optical wavefront relay
configuration such as that
disclosed inUS20100208203 can be used.
1001191 Other functions can also be added to the described example
embodiments. Fig.
8 shows an embodiment in which a dichroic or long-wavelength-pass beam
splitter 860 is
employed to reflect at least a portion of light for general eye imaging and
eye fixation and to
substantially transmit the SLD spectral range near infrared light for
wavefront sensing. The
dichroic or long-wavelength-pass beam splitter 860 should have a large enough
light
interception window to ensure that the wavefront from the eye over a desired
eye diopter
measurement range is fully intercepted without being disturbed by the edge of
the beam
splitter window.
1001201 The reflection of the dichroic or long-wavelength-pass beam
splitter can serve
two functions. The first is to direct the visible or near infrared spectral
portion of light
returned from the eye to an image sensor 862 so that a live eye pupil image
can be processed
and displayed to serve various purposes such as helping a clinician in
aligning the eye with
respect to the wavefront sensor. The source of the light returned from the eye
is an
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illumination light source used, for example, in a surgical microscope, ambient
room light or
light emitted directly from the wavefront sensor module. The second function
is to direct an
image of a visible fixation target 864 to the patient eye so that the eye can
have a target on
which to fixate if such fixation is needed.
1001211 Further down this reflected light beam path is a small beam
splitter 866 that
splits/combines the fixation target light beam and the image sensor light
beam. This small
beam splitter 866 can have various spectral properties. For example, it can be
a simple 50:50
broad band beam splitter designed to operate in the visible and/or near
infrared spectral
range. However, if the fixation light source 864 has a relatively narrow
spectral width, then,
for better optical efficiency, the reflection spectrum of this small beam
splitter 866 can be
made to match the fixation source spectrum to allow good reflection of the
fixation light and
to transmit the rest of the spectrum to the image sensor 862.
1001221 The lens 868 in front of the image sensor 862 can be designed
to provide the
desired optical magnification for the live image of the anterior or iris or
pupil of the patient's
eye on a display. It can also be a dynamic lens used to adjust the focal
length if needed to
ensure that the image sensor plane is conjugate with the eye pupil plane so
that a clear eye
pupil image can be obtained. It can also be a zoom lens so that the
clinician/surgeon can use
it to focus on either the cornea or the retina and to change the magnification
as desired.
Digital zooming can also be employed here.
1001231 The lens 870 in front of the fixation target 864 can be designed to
provide the
patient's eye with a comfortable fixation target of a desired size and
brightness. It can also be
used to adjust the focal length to ensure that the fixation target is
conjugate with the retina of
the eye, or to fixate the eye at different distances or even to fog the eye
per the need of the
clinician/surgeon. The fixation light source 864 can flash or blink or change
colors at a rate
desired to differentiate it from, for example, the illumination light of a
surgical microscope.
The fixation target 864 can be an image such as a hot air balloon back
illuminated by a light
source or a micro-display which can display desired patterns, including arrays
of dots, under
control of a clinician/surgeon. In addition, the micro-display based fixation
target can also be
used to guide the patient to gaze in different directions so that a 2D array
aberration map of
the eye can be generated which can be used to asses the visual acuity of a
patient's non-
central or peripheral vision.
1001241 The fixation target, the eye anterior image, and/or other
information could also
be transmitted back to the microscope and made visible through the oculars
(not shown).
This information would be projected coaxially with the observer's line of
sight by way of a
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dichroie or beam splitter through a series of lenses or physical distance that
would be
coplanar to the microscope or bio-microscopes working distance.
1001251 The image sensor 862 can be a black/white or color CMOS/CCD
image sensor
and the fixation light source can be a red or green or other color light
emitting diode (LED)
with its output optical power dynamically and/or manually controllable, based
on different
background lighting conditions. For example, when a relatively strong
illumination beam
from a surgical microscope is turned on the brightness of the fixation light
source can be
increased to enable the patient to easily find the fixation target and fixate
on it.
[001261 In addition to providing a live eye pupil image, the image
sensor signal can
also be used for other purposes. For example, the live image can be displayed
on a heads-up
display or displayed on a semi-transparent micro-display incorporated in the
eye piece of a
surgical microscope.
1001271 The live image can be used to detect the size and transverse
position of the eye
pupil. When it is found that the size of the pupil is small and/or moved
relative to the
wavefront sensor the mechanism for selecting and/or sampling and/or shifting
the wavefront
can be driven using the information from the image sensor to sample only a
region of the
wavefront centered on the patient's pupil. In other words, the pupil size and
location
information can be used in a closed loop manner for the automatic and/or
dynamic
adjustment and/or the scaling of wavefront sampling. Thus the active wavefront
sampling
apertures and/or the scanner can implement eye tracking. This capability of
continuously
tracking the pupil using internal adjustments and without moving the wavefront
sensor and/or
the surgical microscope to which the wavefront sensor is attached or otherwise
interfering
with its use enables continuous measurement of the patient's wavefront error
through the
surgical procedure.
1001281 The wavefront sensor itself can also provide information for pupil
tracking
because the intensity of light in the sampled wavefront falls off at the edge
of the patient's
pupil, i.e., where the iris begins to block light returning from the retina.
Thus the intensity
detected by the wavefront sensor can provide a map of the patient's pupil,
which can be used
to center the wavefront sampling more accurately on the patient's pupil.
1001291 In addition, either the image sensor or the wavefront sensor
derived eye pupil
position information can be used to provide a feed back signal to drive the
scan minor 880 to
enable the SLD beam to follow the eye movement so that the SLD beam always
enters the
cornea from the same cornea location as intended to prevent, for example, the
specularly
reflected SLD beam returned by the cornea from entering the wavefront sensor's
PSDs. The
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SLD beam can also be imaged by the image sensor for centering of the eye or
for
intentionally offsetting the SLD beam from the center of the pupil or for
providing
feedback/guidance to determine the position of the eye relative to the SLD
beam. The object
beam scanner 812 can also be tuned with a proper offset to follow the eye
pupil movement.
1001301 Furthermore, when it is found that there are obstructions in the
optical path,
such as when the eye is being irrigated with water, or optical bubbles are
present, or the eye
lid, facial skin, a surgeon's hand, or a surgical tool or instrument is in the
image sensor's
view field and is blocking the wavefront relay beam path, then the wavefront
data can be
abandoned to exclude the "dark" or "bright" data and, at the same time, the
SLD 834 can be
turned off.
1001311 In some example embodiments, a qualitative and/or quantitative
wavefront
measurement result can be overlaid onto the display of the live eye pupil
image captured by
the image sensor 862. Furthermore, the wavefront measurement result overlaying
the live eye
pupil image can be updated at a rate so that there is low latency between any
change in the
refractive state and the report of the changed refractive state by the
wavefront sensor. This
updating can be achieved by averaging the detected wavefront data over a
desired period and
updating the qualitative and/or quantitative measurement result overlaying the
live eye image
with a desired update rate that is preferred by a surgeon.
1001321 It should be noted that the image sensor can be individually
incorporated into
the configuration of either Fig. 3a or Fig. 6 to operate independently of the
fixation target.
Meanwhile, the fixation target can also be individually incorporated into the
configuration of
either Fig. 3a or Fig. 6 to operate independently of the image sensor.
1001331 In should also be noted that the wavefront sensor of the
example embodiments
can be integrated with various ophthalmic instruments for eye wavefront
measurements. Fig.
9 shows one example of its integration with a surgical microscope 910 which
allows the
viewing of a patient's eye while the eye wavefront is continuously being
measured. In this
integration, a beam-splitter 915 is inserted along the line of sight 903, from
the eye of the
microscope user to the patient's eye, to create a second optical path linldng
the wavefront-
measurement system 900 and patient's eye 938. Preferably the beam-splitter 915
is a
dichroic beam-splitter reflecting near infrared light while allowing most of
the visible
spectrum to pass through to the user of the microscope.
1001341 With this configuration, the wavefront measurement system 900
can emit light,
preferably near infrared light, toward the retina of patient's eye 938 from
which some of the
scattered light will be returned from the retina to the wavefront sensor. The
scattering point
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on the retina returns some light, with a wavefront 901, which is relayed to
the wavefront
sampling plane of the wavefront measurement system 900, and its deviations
from a plane or
from the inherently aberrated wavefront of the wavefront sensor module if
there is inherence
wavefront aberration reveal the aberrations or the refraction of the patient's
eye.
1001351 Fig. 10 shows the integration of the presently disclosed wavefront
sensor with
a slit-lamp bio-microscope. Again, a beam-splitter 1015 can be inserted along
the line of sight
1003 from the eye of the slit-lamp bio-microscope user to the patient's eye,
to create a second
optical path linking the wavefront-measurement system 1000 and patient's eye
1038. Note
that the same design of the wavefront sensor can be used in each application,
although a
different design with a different working distance and the associated changes
is also an option
depending on the requirement of a particular ophthalmic instrument.
1001361 In practice, preferably the same design of the wavefront sensor
is used both
with a slit-lamp bio-microscope for patient examination before and after
surgery and with a
surgical microscope during refractive surgery. We use the term 'ophthalmic
instrument' to
refer to either type of ophthalmic microscope and/or other ophthalmic
instrument such as a
fundus camera. Preferably, the wavefront sensor should not require special
alignment or
focusing of the microscope or otherwise interfere with normal use of the
ophthalmic
instrument.
1001371 In addition, the example embodiments of the wavefront sensor
can also be
integrated with a femto-second laser or an excimer laser that is used for LA
SIK or natural eye
lens fracturing as well as cornea incision/cutting. The live eye image and the
wavefront signal
can be combined to indicate if optical bubble(s) or other optical non-
uniformity is/are present
in the eye or anterior chamber before, during and after an eye surgical
operation. The
wavefront information can also be used to directly guide the LASIK procedure
in a closed
loop manner.
1001381 These embodiments can also be deployed to measure optics, eye
spectacles or
glasses, 101, and/or guide the cuffing/machining devices that create the
optics.
1001391 These embodiments can also be adapted to microscopes for cell
and /or
molecular analysis or other metrology applications. The example embodiments
can also be
used for lens crafting, spectacle confirmation, micro-biology applications
etc.
1001401 Although various example embodiments that incorporate the
teachings of the
present invention have been shown and described in detail herein, those
skilled in the art can
readily devise many other varied embodiments that still incorporate these
teachings.
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