Note: Descriptions are shown in the official language in which they were submitted.
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HIGH DEFINITION AND EXTENDED DEPTH OF FIELD INTRAOCULAR LENS
PRIORITY CLAIM
[0001] The
present application claims priority to U.S. Patent
Application 16/380,622 entitled "HIGH DEFINITION AND EXTENDED
DEPTH OF FIELD INTRAOCULAR LENS" filed April 10, 2019. The
contents of the above referenced application are incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The
human eye often suffers from aberrations such as
defocus and astigmatism that must be corrected to provide
acceptable vision to maintain a high quality of life. Correction
of these defocus and astigmatism aberrations can be accomplished
using a lens. The lens can be located at the spectacle plane,
at the corneal plane (a contact lens or corneal implant), or
within the eye as a phakic (crystalline lens intact) or aphakic
(crystalline lens removed) intraocular lens (IOL).
[0003] In
addition to the basic aberrations of defocus and
astigmatism, the eye often has higher-order aberrations such as
spherical aberration and other aberrations. Chromatic
aberrations, aberrations due to varying focus with wavelength
across the visible spectrum, are also present in the eye. These
higher-order aberrations and chromatic aberrations negatively
affect the quality of a person's vision. The negative effects
of the higher-order and chromatic aberrations increase as the
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pupil size increases. Vision with these aberrations removed is
often referred to as high definition (HD) vision.
[0004] Presbyopia is the condition where the eye loses its
ability to focus on objects at different distances. Aphakic
eyes have presbyopia. A standard monofocal IOL implanted in an
aphakic eye will restore vision at a single focal distance. To
provide good vision over a range of distances, a variety of
options can be applied, among them, using a monofocal IOL
combined with bi-focal or progressive addition spectacles. A
monovision IOL system is another option to restore near and
distance vision - one eye is set at a different focal length
than the fellow eye, thus providing binocular summation of the
two focal points and providing blended visions.
[0005] Monovision is currently the most common method of
correcting presbyopia by using IOLs to correct the dominant eye
for distance vision and the non-dominant eye for near vision in
an attempt to achieve spectacle-free binocular vision from far
to near. Additionally IOLs can be bifocal or multifocal. Most
IOLs are designed to have one or more focal regions distributed
within the addition range. However, using elements with a set
of discrete foci is not the only possible strategy of design:
the use of elements with extended depth of field (EDOF), that
is, elements producing a continuous focal segment spanning the
required addition, can also be considered. These methods are
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not entirely acceptable as stray light from the various focal
regions degrade a person's vision.
[0006]
What is needed in the art is an improved virtual
aperture IOLto overcome these limitations.
SUMMARY OF THE INVENTION
[0007]
Disclosed is a virtual aperture integrated into an
intraocular lens (IOL). The construction and arrangement permit
optical rays which intersect the virtual aperture and are widely
scattered across the retina, causing the light to be virtually
prevented from reaching detectable levels on the retina. The
virtual aperture helps remove monochromatic and chromatic
aberrations, yielding high-definition retinal images. For
a
given definition of acceptable vision, the depth of field is
increased over a larger diameter optical zone IOL. Eyes with
cataracts can have secondary issues due to injury, previous eye
surgery, or eye disorder that would not be well corrected with
normal IOL designs.
Examples of eyes with complications
include: asymmetric astigmatism, keratoconus, postoperative
corneal transplant, asymmetric pupils, very high astigmatism,
and the like.
Because of its ability to remove unwanted
aberrations, our virtual aperture IOL design would be very
effective in provided enhanced vision compared to normal large
optic IOLs.
[0008] An
objective of the invention is to teach a method of
making thinner IOLs since the optical zone can have a smaller
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diameter, which allows smaller corneal incisions and easier
implantation surgery. Eyes with cataracts can have secondary
issues due to injury, previous eye surgery, or eye disorder that
would not be well corrected with normal IOL designs. Examples
of eyes with complications include: asymmetric astigmatism,
keratoconus, postoperative corneal transplant, asymmetric
pupils, very high astigmatism, and the like.
Because of its
ability to remove unwanted aberrations, the disclosed virtual
aperture IOL design is effective in providing enhanced vision
compared to normal large optic IOLs.
[0009]
Another objective of the invention is to teach a
virtual aperture IOL that exhibits reduced monochromatic and
chromatic aberrations, as well as an extended depth of field,
while providing sufficient contrast for resolution of an image
over a selected range of distances.
[0010]
Still another objective of the invention is to teach
a virtual aperture IOL that provides a smaller central thickness
compared to other equal-powered IOLs.
[0011]
Another objective of the invention is to teach a
virtual aperture that can be realized as alternating high-power
positive and negative lens profiles.
[0012] Yet
still another objective of the invention is to
teach a virtual aperture that can be realized as high-power
negative lens surfaces.
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[0013] Another objective of the invention is to teach a
virtual aperture that can be realized as high-power negative
lens surfaces in conjunction with alternating high-power
positive and negative lens profiles.
[0014] Yet another objective of the invention is to teach a
virtual aperture that can be realized as prism profiles in
conjunction with alternating high-power positive and negative
lens profiles.
[0015] Still another objective of the instant invention is
to overcome these limitations by providing a phakic or aphakic
IOL which simultaneously: provides correction of defocus and
astigmatism, decreases higher-order and chromatic aberrations,
and provides an extended depth of field to improve vision
quality.
[0016] Another objective of the invention is to teach a
virtual aperture that can be employed in phakic or aphakic IOLs,
a corneal implant, a contact lens, or used in a cornea laser
surgery (LASIK, PRK, etc.) procedure to provide an extended
depth of field and/or to provide high-definition vision.
[0017] Yet another objective is to provide an IOL for eyes
with complications such as asymmetric astigmatism, keratoconus,
postoperative corneal transplant, asymmetric pupils, very high
astigmatism, and the like.
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[ 0018 ] Still another objective is to provide an IOL capable
of removing unwanted aberrations to provide enhanced vision
compared to normal large optic IOLs.
[0019] Another objective of the invention is to teach
replacement of the virtual aperture with an actual opaque
aperture and realize the same optical benefits as the virtual
aperture.
[0020] Other objectives and further advantages and benefits
associated with this invention will be apparent to those skilled
in the art from the description, examples and claims which
follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Fig. 1 illustrates the basic method of reducing
monochromatic aberrations using pupil size;
[0022] Fig. 2 (A&B) illustrates the basic method of reducing
chromatic aberrations using pupil size;
[0023] Fig. 3 (A&B) illustrates the basic concept of the
virtual aperture to limit the effective pupil size;
[0024] Fig. 4 illustrates the virtual aperture as a high-
power lens section integrated into an IOL;
[0025] Fig. 5 illustrates the virtual aperture as a negative
lens section;
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[ 002 6 ]
Fig. 6 (A&B) illustrates the virtual aperture as a
negative lens (or prism) section in conjunction to a high-power
lens section;
[0027]
Fig. 7 (A&B) illustrates using the virtual aperture
to prevent the negative effect of a small optic zone;
[0028]
Fig. 8 illustrates lens A example of an oblong shaped
optical zone and lens B example of a circular shaped optical
zone;
[0029] Fig. 9 illustrates azimuthally symmetric radial
profiles;
[0030] Fig. 10 illustrates symmetric radial profiles
comparing elements A, B, C, D, & E;
[0031]
Fig. 11 illustrates two-dimensional lens regions; and
[0032]
Fig. 12 illustrates the geometry for one of the two-
dimensional high-power lenses.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0033]
Detailed embodiments of the instant invention are
disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention,
which may be embodied in various forms.
Therefore, specific
functional and structural details disclosed herein are not to
be interpreted as limiting, but merely as a basis for the claims
and as a representation basis for teaching one skilled in the
art to variously employ the present invention in virtually any
appropriately detailed structure.
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[ 0034 ]
Figure 1 illustrates a single converging lens I
centered on an optical axis 2. An incident ray 3 is parallel
to the optical axis and will intersect the focal point 4 of the
lens. If the observation plane 5 is located a further distance
from the focal point, the incident ray will continue until it
intersects the observation plane. If we trace all incident rays
with the same ray height as incident ray 3, we will locate a
blur circle 6 on the observation plane. Other incident rays
with ray height less than incident ray 3 will fall inside this
blur circle 6. One such ray is incident ray 7 which is closer
to the optical axis than incident ray 3. Incident ray 7 also
intersects the focal point 4 and then the observation plane 5.
Tracing all incident rays with a ray height equal to incident
ray 7 traces out blur circle 8 which is smaller than blur circle
6.
[0035] The
optical principle represented here is that as the
height of parallel incident rays is reduced, the corresponding
blur circle is also reduced.
This simple relationship is
applicable to the human eye. Stated another way, for a given
amount of defocus (dioptric error) in the eye, vision is improved
as the height of incident rays is reduced. This principle is
used when someone squints in an attempt to see an out-of-focus
object more clearly.
[0036] The
tracing in Figure 1 is for a single wavelength of
incident light. For polychromatic light, three wavelengths in
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this case, we have the situation in Figure 2. It is well known
for the components of the eye and typical optical materials
that, as wavelength increases, the refractive index decreases.
In Figure 2A, a converging lens 21 has optical axis 22. An
incident ray 23 consists of three wavelengths for blue (450 nm),
green (550 nm), and red (650 nm) light. Due to different indices
of refraction for the three wavelengths, the blue light ray 24
is refracted more than the green light ray 25, and the green
light ray is refracted more than the red light ray 26. If the
green light ray is in focus, then it will cross the observation
plane 27 at the optical axis. The chromatic spread of these
three rays lead to a chromatic blur circle 28 on the observation
plane. In Figure 2B, the incident chromatic ray 29 has a lower
ray height than the chromatic ray 23 in 2A. This leads to the
smaller chromatic blur circle 33 at the observation plane. Thus,
just as for the monochromatic of Figure 1, chromatic blur is
decreased as the chromatic ray height is decreased.
[0037]
Figures 1 and 2 illustrate that decreasing ray height
(decreasing the pupil diameter) decreases both monochromatic and
chromatic aberrations at the retina, thus increasing the quality
of vision. Another way to describe this is that the depth of
field is increased as the ray height is decreased.
[0038]
Figure 3A illustrates a converging lens 34 with
optical axis 2 and aperture 35.
Incident ray 36 clears the
aperture and thus passes through the lens focal point 37 and
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intersects the observation plane 38 where it traces a small blur
circle 39. Incident ray 40 is blocked by the aperture, and thus
it cannot continue to the observation plane to cause a larger
blur circle 41. An aperture which limits the incident ray height
reduces the blur on the observation plane. In
Figure 3B we
illustrate what we describe as a "virtual aperture". That is,
it is not really an aperture that blocks rays, but the optical
effect is nearly the same. Rays 43 which propagate through the
virtual aperture 42 are widely spread out so there is very little
contribution to stray light (blurring light) at any one spot on
the observation plane.
This is the principal mechanism of
operation of the IOL invention. Occasionally, a few months to
a few years following cataract surgery and IOL implantation, a
condition called posterior capsule opacification (PCO) develops
over the clear posterior capsule and can interfere with quality
vision. The incidence of PCO has been reported to be in the
range of 5% to 50% of eyes undergoing cataract surgery and IOL
implantation.
Treatment to remove the PCO often involves
intervention with a Nd:YAG laser to perform a posterior
capsulotomy. In this case, the laser is focused through the IOL
to perform the capsulotomy. If the virtual aperture were instead
opaque, such as a true aperture, then this treatment would be
inhibited. The
disclosed virtual aperture is intentionally
designed to provide the benefits of a small aperture while at
the same time allowing a YAG capsulotomy to treat PCO.
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[ 0039 ]
Figure 4 illustrates a basic layout of an IOL which
employs the virtual aperture. In this figure, a central optical
zone 46 provides correction of defocus, astigmatism, and any
other correction required of the lens. Generally, for an IOL
using a virtual aperture, the central optical zone diameter is
smaller than a traditional IOL. This leads to a smaller central
thickness which makes the IOL easier to implant and allows a
smaller corneal incision during surgery. The virtual aperture
48 is positioned further in the periphery and the IOL haptic 50
is located in the far periphery. The
virtual aperture is
connected to the optical zone by transition region 47 and the
haptic is connected to the virtual aperture by transition region
49. The
transition regions 47 and 49 are designed to ensure
zero-order and first-order continuity of the surface on either
side of the transition region. A common method to implement
this is a polynomial function such as a cubic Bezier function.
Transition methods such as these are known to those skilled in
the art.
[0040] In
the preferred embodiment, the virtual aperture zone
48 is a sequence of high-power positive and negative lens
profiles.
Thus, light rays which intersect this region are
dispersed widely downstream from the IOL. These profiles could
be realized as sequential conics, polynomials (such as Bezier
functions), rational splines, diffractive profiles, or other
similar profiles, as long as the entire region properly
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redirects and/or disperses the refracted rays. The preferred
use is smooth high-power profiles over diffractive profiles as
this simplifies manufacturing the IOL on a high-precision lathe
or with molds. As
known to those skilled in the art, the
posterior side of the haptic should include a square edge to
inhibit cell growth leading to posterior capsule opacification.
[0041]
Figure 5 illustrates another profile for the virtual
aperture zone 51, namely a diverging lens profile. Note that
this requires a thicker edge profile than the approach in Figure
4. In Figure 6A we show a close up of the preferred high-powered
alternating positive and negative lens profiles with the
incident and transmitted rays. Figure 6B illustrates the effect
of combining the profile in 6A with either an underlying prism
or negative lens. In this case not only are the emergent rays
scattered widely, they are directed away from the eye's macula,
or central vision section of the retina, again, at the cost of
a wider lens edge.
[0042]
Figure /A illustrates a high-power IOL 60, usually
with a relatively small optical diameter and large central
thickness.
When the eye's pupil is larger than the optical
zone, incident rays 64 can miss the optic entirely and only
intersect the haptic 61 on their way to the retina 63. This
situation would cause noticeable artifacts in the peripheral
vision of the eye. Incident rays 62, which intersect the optic
zone as expected, are correctly refracted to the central vision
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of the retina. In Figure 7B we illustrate the same optic, but
now with a virtual aperture 65 between the optic and the haptic.
In this case, incident rays 64 which intersect the lens outside
of the optical zone, are dispersed across the retina causing no
apparent artifacts.
[0043]
Taken together, these characteristics of an IOL which
incorporates the virtual aperture can accurately be described
as high definition (HD) and extended depth of field (EDOF).
[0044] The
basic layout of the virtual aperture IOL is
illustrated in Figure 4. In
the preferred embodiment, the
diameter of the central optical zone 46 is 3.0 mm and the width
of the virtual aperture 48 is 1.5 mm. Thus, the combination of
central optical zone and virtual aperture is a 6.0-mm diameter
optic, which is similar to common commercially available IOLs.
[0045]
Spherical, Toric and zero aberrations optic zone. A
significant portion of cataract patients have astigmatism in
their cornea. After removal of the crystalline lens, the
remaining optical system of the astigmatic cornea eye is ideally
corrected with a toric, or astigmatic lens. For these patients,
the central optical portion of our lens is made toric to provide
improved visual correction. In
addition, even though the
optical portion is small, there is still some amount of spherical
aberrations that could be corrected.
Thus, the optimally
corrected optical zone would provide spherical aberration
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correction for all lenses and toric correction for those
patients who have corneal astigmatism.
[0046] The
toric correction is easily made by those skilled
in the art by providing two principle powers at two principle
directions which would be aligned with the eye's corneal
astigmatic powers.
[0047] The
spherical aberrations for either the spherical or
toric lens are corrected by employing a conic profile on one or
more surfaces of the lens. Such a lens is said to have zero
aberrations as there are zero monochromatic aberrations in the
lens for an on-axis, distant object. The apical radius Ra of
the conic profile is computed as usual for the desired paraxial
power of the lens. A conic constant K is then selected based
upon the lens material index of refraction, the lens center
thickness, and the shapes of the front and back surface of the
lens.
[0048] In
the case where the correction is to be astigmatic,
at least one of the lens surface shapes is biconic, having a
conic profile in two orthogonal principal directions. In the
preferred embodiment, the toric optic has an equal biconvex
surface design where each surface is biconic. The
non-toric
optic has an equal biconvex surface design where each surface
is conic. In both the biconic or conic surface case, the optimal
conic constant K for the surfaces is determined using optical
ray tracing known to those skilled in the art.
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[ 004 9 ] Multiple focal points.
Some patients may prefer a
multi-focal point optic providing vision correction for specific
distances. One
example is a bifocal optic which generally
provides focusing power for both near and distant vision.
Another example is a trifocal optic which provides focusing
power for near, intermediate, and distant vision. In
either
case, to implement the multi-focal points IOL, the optical zone
is modified to yield these focal zones using refractive or
diffractive optical regions and the virtual aperture remains
outside the last focal zone.
[0050] In
some applications, the virtual aperture can appear
as an annular region with optical zones on each side of the
annular region. The shape of the annular virtual aperture can
also be free form, for example to accommodate an astigmatic
optical zone or non-symmetric haptic region.
This is
illustrated in Figure 8. In this Figure, lens A indicates an
oblong shaped optical zone and so the inner contour of the
virtual aperture must adapt to the shape. The inner haptic zone
contour is circular, so the outer virtual aperture contour is
circular. In this Figure, lens B depicts the optical zone as
circular, so the virtual aperture inner contour is circular.
The inner haptic contour is oblong, so the outer virtual aperture
contour is oblong. In
each case there are transition zones
between each of the zones to smoothly connect the regions so
that no visual artifacts are introduced into the eye.
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Alternatively, the transition regions can be of variable width
so that the inner and outer virtual aperture contours can be any
desired shape.
[0051] The
IOL designs contemplated here can be made of any
biocompatible optical material normally used for IOLs including
hard and soft materials. They also can be manufactured using
CNC machines or molds or other methods used to manufacture IOLs.
The virtual aperture can be implemented as a one-dimensional
profile that is symmetric in the azimuthal direction or a two-
dimensional profile that implements tiny lens regions.
[0052] In
Figure 9, illustrated is azimuthally symmetric
radial profiles. The profiles can be all the same or adjusted
in the azimuth direction. These profiles can be refractive or
diffractive in nature. Although, eight distinct radial profiles
are illustrated, the radial profiles are continuous in the
azimuth direction. The
radial profiles can have alternating
positive and negative power, all positive power, or all negative
power sections. The connections between all the power regions
are smooth to prevent visual artifacts.
[0053] In
Figure 10, illustrated are other symmetric radial
profiles include combinations of planar, negative power, and
ramp base shapes in addition to or instead of the high-power
curves indicated in Figure 8. Referring to Figure 10, element
A depicts a simple plane base shape. In Figure 10, element B
depicts a negative power base shape. This generally negative
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power curved profile can be represented by a portion of a sphere,
a conic, or higher order curve such as a polynomial. Figure 10,
element C depicts a segmented negative power profile of element
B, where the curve has been segmented similar to a Fresnel lens,
to keep the overall lens thickness small. Figure 10, element D
depicts a ramp base shape profile and Figure 10, element E
depicts a segmented version of the ramp base shape, where the
ramp has been segmented similar to a Fresnel lens, to keep the
overall lens thickness small. Although the segmented profiles
of elements C and E are illustrated with sharp discontinuities,
in practice, the boundaries of the segments are implemented
using smooth functions such as filets or Bezier curves to prevent
observable artifacts caused by the sharp discontinuities.
Additionally, a smooth transition region is placed between the
optic zone and the virtual aperture as described elsewhere in
this document. These base shapes can be used in conjunction with
or instead of the high-power features to improve the
effectiveness of the virtual aperture.
[0054] Figure 11 illustrates two-dimensional lens regions
oriented in a polar sampling. The high-power lenses alternate
in positive and negative power in both the radial and azimuthal
directions. Two positive power lenses and two negative power
lenses are illustrated in the figure. The actual geometry of
these two-dimensional polar lenses is on the order of the radial
profiles.
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[ 0055 ]
Alternatively, the two-dimensional high-power lenses
could be all positive or all negative lenses. In this case, the
high-power lenses are separated by small smooth transition
regions (for example, a continuous polynomial interpolator such
as a Bezier curve) to prevent visual artifacts.
This is the
preferred two-dimensional high-power lens structure when there
is more than one lens sample rate in the azimuth direction. In
this case, the individual lenses look like small pillows where
the pillows are above the base surface for positive power lenses
and are below the surface for negative power lenses.
[0056]
Figure 12 illustrates the geometry for one of the two-
dimensional high-power lenses. In the upper right portion of
the figure we show a front view of the high-power lens. There
is a central high-power optical region and a surrounding
transition region. The radial extent of this region is given
by r, the width of the transition region is given by t, and the
azimuthal subtense is given by theta. In the lower left portion
of the figure we show a side view of one of the profiles of the
lens. The central part represents the high-power optical zone
and the two side curves represent the transition zones. The
interface between the optical zone and the transition zones has
zero- and first-order continuity. At the edge of the lens
boundary, the transition is coincident with the virtual aperture
base shape (which is typically a vertical line on the IOL). At
the edge of the lens there is also zero- and first-order
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continuity between the transition curve (typically a polynomial
curve) and the edge. The shape of this small high-power lens
region is set so that the radial extent r is approximately equal
to the arc-length of the center portion of the region.
[0057] The
central optical zone can be designed using
standard IOL design concepts to provide sphere, cylinder, and
axis correction, as well as higher-order correction such as
spherical aberration control. These design concepts are known
to those skilled in the art.
[0058] The
preferred virtual aperture profiles illustrated
in Figure 4 have alternating positive and negative lens profiles
with focal lengths on the order of +/- 1.5 mm.
These lens
surface profiles can be generated using conics, polynomials
(such as cubic Bezier splines), rational splines, and
combinations of these and other curves. The geometry of the
lens profiles is selected to adequately disperse the transmitted
optical rays across the retina and at the same time be relatively
easy to manufacture on a high-precision lathe or with a mold
process. It is also possible to place a smooth surface on one
profile (for example the front surface) and the small high-power
lens profiles on the other surface profile (for example the back
surface).
[0059] Using the preferred virtual aperture profiles
illustrated in Figure 4, the edge thickness of the IOL and the
center thickness of the central optical zone can be quite small,
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even for high-power IOLs. The material of the lens is the same
as those used for other soft or hard IOL designs.
[0060] The
IOL design provides very good, high-definition,
distance vision and the range of "clear vision" can be controlled
by specification of what is meant by "clear vision" (e.g., 20/40
acuity), and the relative size of the central optic zone and the
virtual aperture width. A simple equation [Smith G, Relation
between spherical refractive error and visual acuity, Optometry
Vis. Sci. 68, 591-8, 1991] for estimating the acuity given the
pupil diameter and spherical refractive error is given in
equation (la and lb).
A=kDE
A =-11 D
(i10)
A = acuity in minutes of arc (A = Sd/20), that is, the
minimum angle of resolution
k = a constant determined from clinical studies, mean value
of 0.65
D = pupil diameter in mm
E = spherical refractive error in diopters
Sd = Snellen denominator
[0061] The
second equation is postulated as being more
accurate for low levels of refractive error, and gives a
reasonable result.
For E = 0, A = 1 min of arc or 20/20.
Solving (lb) for E yields equation (2).
E- ______________________________________________________________________ (4
Af D
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Equation (lb) tells us the acuity A given the range of depth of
field (E x 2) in diopters and the pupil diameter D.
Equation (2) tells the range of depth of field in diopters given
the acuity A and the pupil diameter D. For example, for:
Acuity of 20/40, A = 40/20 = 2 min arc
D = 3.0 mm
k = 0.65
E= ________________________________
=0.89
0.65 x 3.0
Depth of field = 2E = 1.8 D. Using (lb),
A = + (0.65 x3.0 x 0.89)2 = 2
[0062] The
concept of the virtual aperture can be employed
in phakic or aphakic IOLs, a corneal implant, a contact lens,
or used in a cornea laser surgery (LASIK, PRK, etc.) procedure
to provide an extended depth of field and/or to provide high-
definition vision. Also, it would be possible to replace the
virtual aperture with an actual opaque aperture and realize the
same optical benefits as the virtual aperture.
[0063] It
is to be understood that while a certain form of
the invention is illustrated, it is not to be limited to the
specific form or arrangement herein described and shown. It
will be apparent to those skilled in the art that various changes
may be made without departing from the scope of the invention
and the invention is not to be considered limited to what is
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shown and described in the specification and any
drawings/figures included herein.
[0064] One
skilled in the art will readily appreciate that
the present invention is well adapted to carry out the objectives
and obtain the ends and advantages mentioned, as well as those
inherent therein. The
embodiments, methods, procedures and
techniques described herein are presently representative of the
preferred embodiments, are intended to be exemplary and are not
intended as limitations on the scope. Changes therein and other
uses will occur to those skilled in the art which are encompassed
within the spirit of the invention and are defined by the scope
of the appended claims.
Although the invention has been
described in connection with specific preferred embodiments, it
should be understood that the invention as claimed should not
be unduly limited to such specific embodiments. Indeed, various
modifications of the described modes for carrying out the
invention which are obvious to those skilled in the art are
intended to be within the scope of the following claims.
22
