Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Device for ophthalmic laser surgery
The invention relates to an apparatus for ophthalmological laser surgery and
to an
associated method.
Pulsed laser radiation finds application in numerous techniques for treating
the
human eye. Local control of the beam focus of the laser beam in the z-
direction (this
means, according to conventional notation, the direction of propagation of the
laser
beam) is always effected with reference to a known reference point or a known
reference surface in the coordinate system of the laser apparatus.
Depending on the type of treatment, differing reference points or reference
surfaces
may serve as reference for the z-control of the beam focus. With some of these
techniques the eye to be treated is pressed against a transparent contact
element
which, with its contact surface facing towards the eye, constitutes a
reference
surface for the positioning of the beam focus in the z-direction. In
particular,
treatment techniques that serve for producing incisions in the ocular tissue
by means
of focused femtosecond laser radiation frequently make use of such contact
elements
by way of z-reference for the laser focus. By the contact element being
pressed
against the eye in such a way that a conforming planar abutment of the eye
against
the contact surface of the contact element facing towards the eye arises, the
contact
element presets the z-position of the anterior surface of the eye. By
referencing of
the beam focus in the z-direction in relation to this contact surface of the
contact
element it is then ensured that the incision or the individual photodisruption
(the
production of an incision in the human eye by means of pulsed femtosecond
laser
radiation is normally based on the effect of so-called laser-induced optical
breakthrough, which results in a photodisruption) is situated at the desired
position
deep within the ocular tissue.
Incisions produced by laser technology occur, for example, in the case of so-
called
femtosecond (fs) LASIK, in which a small anterior cover disc of the cornea,
designated
in specialist circles as a flap, is cut free by means of femtosecond laser
radiation, in
order subsequently, as in the case of classical LASIK technology (LASIK: Laser
In-Situ
Keratomileusis), to fold aside the flap that is still attached to the
remaining corneal
tissue in a hinge region and to process the tissue exposed in this way in
ablating
manner by means of UV laser radiation. Another application for the placement
of intra-
tissue incisions in the ocular tissue is so-called corneal lenticle
extraction, in
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which a small lenticular disc is cut out all round within the corneal tissue
by means of
femtosecond laser radiation. This small disc is subsequently removed through
an
additional incision which is guided out to the surface of the eye (the
additional
incision is produced either by means of a scalpel or likewise by means of
femtosecond laser radiation). Also in the case of corneal grafting
(keratoplasty) or
for other incisions, for example for corneal ring segments, the production of
an
incision in the cornea can be carried out by means of focused pulsed laser
radiation.
For reasons of hygiene, the contact element (applicator) bearing the contact
surface
lo is often a disposable article which has to be exchanged before each
treatment.
Certain manufacturing tolerances cannot normally be ruled out in the
production of
the contact elements, even with the greatest precision of manufacture. After
an
exchange of the contact element, therefore, the z-position of the contact
surface
facing towards the eye may be different ¨ albeit only slightly ¨ from that in
the case
of the contact element used previously. In the case of laser treatments by
means of
focused femtosecond laser radiation, focus diameters that are as small as
possible
are striven for, in order to limit the photodisruptive action locally to be as
restricted
as possible. Modern instruments operate, for example, with focus diameters
within
the low single-digit pm range. Often in the course of the implementation of
zo interventions by means of femtosecond systems the depth of the incision
in the
target tissue has to be defined with extremely high accuracy (incision-depth
tolerances < 5 pm). As described previously, in such interventions the tissue
to be
treated and the optical system of the laser are, as a rule, firmly coupled to
one
another by means of a contact element, in order to obtain the requisite depth
of
incision with corresponding precision in the z-direction. This demands a
correspondingly high accuracy of manufacture of the contact element, which,
however, cannot always be guaranteed. Given diminished precision of
manufacture
of the contact element, the problem therefore arises of an imprecise incision
guidance in the corneal tissue in the z-direction - i.e. the manufacturing
tolerances
for these contact elements enter directly into the inaccuracies for the depth
of
incision in the tissue.
In the state of the art, use is generally made of applicators that have been
manufactured precisely, with corresponding effort. In the course of the
installation
of these applicators the optical system of the laser is adjusted to the
demanded
distance between the optical system and the incision plane on the basis of a
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reference applicator, utilising the interaction between laser radiation and
material.
This is already known from WO 2004/032810, for example.
The spacing between tissue and laser system, and hence directly the real depth
of
incision in the tissue, is substantially determined by the dimension of the
applicator ¨
i.e. by the real optical length of the applicator in the z-direction. This
makes it
necessary, for the purpose of obtaining the requisite precision of the depth
of
incision, that the applicators have to be manufactured with correspondingly
small
tolerances with respect to their dimension (the relative length accuracy lies
clearly
<< 0.1 %), distinctly increasing the production costs of these applicators and
having
a direct effect, particularly in the case of single-use articles that are
required in large
numbers, on the costs of treatment and hence on the so-called costs of
ownership.
From patent publication No. WO 2011/035793, filed by the present applicant, it
is
known to take account of and to equalise inaccuracies of manufacture of the
contact
element. For this purpose, by means of a measuring device a positional
surveying of
the contact surface relative to the direction of propagation of the treatment
laser
beam is carried out and by means of an electronic evaluating and control
arrangement connected to the measuring device the focal location of the
treatment
laser beam is adjusted in a manner depending on the measured position data
acquired by the measuring device.
Although the procedures known from the state of the art take account of
inaccuracies of manufacture of the contact element or attempt to avoid such
inaccuracies through precision that is as high as possible (with, at the same
time,
high costs), they disregard further factors influencing the accuracy of
adjustment of
the focal point in the z-direction.
In addition to the stated manufacturing tolerances, the effective depth of
incision is
dependent on temperature drifts of the dimension of the applicator and also on
the
effective focal length of the overall optical system ¨ i.e. the real optical
length of the
applicator in the direction of propagation of the treatment laser beam and
also the
focal length of the optics of a laser system vary in a manner depending on the
functional temperature range. Within the conventional functional temperature
range
of medical instruments of 15 0C ¨ 35 0C the stated drifts may easily sum to 30
pm to
50 pm. Hence the incision-depth tolerances of < 5 pm being striven for can
only be
obtained with difficulty or can no longer be obtained.
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_
It is an object of the present invention to make available an apparatus for
ophthalmological laser surgery and also an associated method, said apparatus
and said
method enabling a more precise laser treatment of an eye.
Certain exemplary embodiments can provide an apparatus for ophthalmological
laser
surgery, comprising: an optical imaging system for directing a treatment laser
beam
onto a focal point; a temperature-measuring device for measuring a temperature
assigned to the imaging system; an electronic control arrangement connected to
the
temperature-measuring device, which is configured to control a focal-point
setting
depending on the measured temperature; a contact surface for a shaping
abutment of
an eye to be treated; and measuring device for positional surveying of the
contact
surface relative to the direction of propagation of the treatment laser beam,
the
measuring device providing measured position data that are representative of
the
measured position of the contact surface at one or more places on the contact
surface,
the electronic control arrangement is configured to preset the focal point
depending on
the measured position data.
Other embodiments provide an apparatus for ophthalmological laser surgery is
provided that comprises the following components: an optical imaging system
for
directing a treatment laser beam onto a focal point, a temperature-measuring
device for
measuring a temperature assigned to the imaging system, and an electronic
control
arrangement connected to the temperature-measuring device, which is configured
to
control the focal-point setting in a manner depending on the measured
temperature.
In this connection the apparatus may include a contact surface for the shaping
abutment of an eye to be treated and also a radiation-source for providing the
treatment laser beam. Furthermore, the imaging system may have optical
components
for directing the treatment laser beam through the contact surface onto the
eye.
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The invention enables a control and/or readjustment of a position, for example
a preset
position, of the laser-beam focus in the z-direction (corresponding to the
direction of
propagation of the treatment laser beam) in a manner depending on the measured
temperature of the critical components crucially influencing the depth of
focus (e.g. the
objective, the component for beam expansion etc.) and around the apparatus.
Presetting of the focal point may be effected in various ways.
The position of the focus in the z-direction may be preset, for example, by
the z-
position of the contact surface with respect to a given reference point in a
fixed
coordinate system of the laser-surgical apparatus being known. In this
connection
use is preferentially made of a patient adapter (applicator), the real optical
length of
which in the direction of propagation of the treatment laser beam (z-
direction) has been
established with high accuracy, so that the focal point can be preset to the
known
length. Changes in the length of the applicator or changes in the effective
focal length
of the optical components contained in the apparatus by reason of changing
temperature around the apparatus can be detected by the temperature-measuring
device and taken into account appropriately by the control arrangement.
Similarly, it
is conceivable that the effective optical spacing (the real optical length)
between the
surface of the applicator (the contact surface) facing towards the eye
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and the surface facing away from the eye (the surface facing towards the
optical
components of the apparatus) has already been measured outside the apparatus
and, for example, embossed on the associated applicator via a coding. This
coding
can then be read out by the apparatus, for example automatically or manually,
and
relayed to the control arrangement. On the basis of the value that has been
read
out, the control arrangement can firstly preset the focal point.
Alternatively, for the purpose of presetting the focal point the z-position of
the
contact surface with reference to the given reference point can be measured.
For
this purpose the apparatus preferably has a measuring device for positional
surveying of the contact surface relative to the direction of propagation of
the
treatment laser beam. For this purpose the measuring device comprises, for
example, a second radiation-source providing a measuring beam. The optical
components are then preferentially designed and arranged for the purpose of
also
directing the measuring beam through the contact surface onto the eye. By
means
of the measuring beam, the measuring device can preferentially provide
measured
position data that are representative of the measured position of the contact
surface
at at least one place on the same and can relay the ascertained measured
position
data to the control arrangement. In response to this, the electronic control
arrangement can preset the focal point in a manner depending on the measured
position data. For differing contact elements a differing z-position of the
contact
surface in the coordinate system or a differing effective optical spacing may
result,
depending on the accuracy of production. By evaluation of the measurement,
carried
out by the measuring device, of the z-position of the contact surface and/or
of the
real optical length of the applicator, firstly the focal point in the z-
direction can be
preset, so that production inaccuracies are diminished or avoided. On the
basis of
the measured temperature, the preset focal point can subsequently be adapted
or
readjusted.
Adaptation or readjustment of the preset focal point may, for example, be
effected at
predetermined time-intervals by a repeated measurement of the temperature by
the
temperature-measuring device being effected after predetermined periods of
time.
For example, a readjustment may be effected when the measured temperature
exceeds the previously measured temperature by a predetermined threshold. In
such a case a considerable temperature drift would have to be assumed, which
necessitates a readjustment of the focal point. A diminution of the
predetermined
threshold enables a more accurate but more elaborate readjustment of the focal
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point. The predetermined time-intervals and the predetermined threshold are
preferentially saved in a memory connected to the control arrangement, so that
the
control arrangement can read out these values as required and can control the
temperature-measuring device and also the readjustment of the focal point
appropriately. It is also conceivable that a renewed temperature measurement
is
effected only when, for example, an appropriate instruction is input by a user
into
the temperature-measuring device or into components connected thereto.
The temperature-measuring device may comprise one or more temperature sensors
io which are arranged on one or more of the optical components and
connected to the
control arrangement. The optical components preferably constitute, on the one
hand, a scan unit for deflecting the treatment laser beam in a plane (x-y
plane)
orthogonal to the beam path thereof or a 3D scan unit for three-dimensional
deflecting of the treatment laser beam and also, on the other hand, focusing
optics
for focusing the treatment laser beam to the laser-beam focus. In this case,
preferentially two temperature sensors in each instance are arranged on the
scan
unit and on the focusing optics. However, also one temperature sensor or more
than
two temperature sensors may be arranged in each instance on the scan unit and
on
the focusing optics.
For the purpose of adapting the focal point, the optical components comprise
at least
one controllable optical element. For example, the controllable optical
element is
constituted by a lens that is positionally variable in the direction of
propagation of the
treatment laser beam. For the purpose of controlling the lens, the control
arrangement can generate, as a function of the measured temperature, an
actuating
variable for readjusting the preset focal point. The lens is, for example,
mechanically
displaceable or repositionable along the optical beam path. In this case the
control
arrangement has preferably been set up to vary the position of the
positionally
variable lens by the ascertained actuating variable for the purpose of
adapting the
focal point.
Alternatively, it is conceivable to use a controllable liquid lens of variable
refractive
power. With unchanged z-position and also otherwise unchanged setting of the
focusing objective, a z-shift of the beam focus can be obtained by displacing
a
longitudinally adjustable lens or by variation of the refractive power of a
liquid lens,
in order thereby to adapt the focal point to the altered temperature. It will
be
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understood that for the purpose of z-adjustment of the beam focus other
components are also conceivable, such as a deformable mirror for instance.
The control arrangement may further have a memory unit or may be connected to
such a unit in which the dependence of the focal point on the temperature is
stored
as a function. The temperature dependences of all the materials used in the
apparatus and of all the spacings occurring in the apparatus (for example, the
spacings of the optical components from one another or the real optical length
of the
applicator) can be used in order to calculate a temperature sensitivity of the
effective
focal length of the optical components starting from a reference temperature.
The
temperature sensitivity is preferentially ascertained and recorded separately
for the
scan unit and the focusing optics, but it may also be calculated for these
jointly. The
ascertained temperature sensitivity may be saved as a family of curves in the
memory unit and, as required, may be interrogated by the control arrangement
and
used for the purpose of adapting the focal point on the basis of the stored
family of
curves.
By virtue of the temperature being taken into account in the readjustment of
the
focal point of the treatment laser beam by the control arrangement, changes in
the
effective focal length as well as changes in the effective optical spacing of
the
applicator occurring by reason of fluctuations in temperature are compensated.
By
this means, it is ensured that an incision pattern or, to be more exact, a
pattern of
photodisruptions to be realised in the eye is in fact situated at the desired
place deep
within the eye (that is to say, at the desired place in the z-direction). In
this manner,
highly precise depths of incision are possible, for example in the case of the
production of a LASIK flap, in the case of corneal lenticle extractions or in
cases of
keratoplasty.
The control arrangement may furthermore be configured to generate, in the
course
of the readjustment of the focal point in the z-direction at several different
places in
an x-y plane orthogonal to the z-direction, differing actuating variables for
the
controllable optical element. As a result, it is possible, for example, to
compensate
individually variably strong effects of the changes in temperature on the
position of
the contact surface in the x-y plane.
The measuring device is preferentially an optical-coherence interferometric
measuring device and possesses to this end an optical interferometer.
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The contact surface will frequently be part of an exchangeably arranged
disposable
component, for example a single-use applicator. However, it is to be
emphasised
that the invention does not presuppose a disposable nature of the element
bearing
the contact surface. The invention is equally employable in configurations
with a
permanently incorporated or at least repeatedly usable contact surface.
The contact surface is preferably constituted by a transparent applanation
plate or a
transparent contact lens. Applanation plates possess, at least on their flat
side facing
towards the eye, a plane applanation face with which a levelling of the front
of the
eye is achieved. The use of applanation plates for the purpose of referencing
the
eye to be treated is normally favourable from the point of view of a high beam
quality of the laser radiation. Nevertheless, within the scope of the
invention it is
equally possible to use by way of contact element a contact lens with a,
typically,
concavely or convexly shaped lens surface facing towards the eye. The
advantage of
such contact lenses is, for example, a smaller rise in the intraocular
pressure when
pressing onto the eye.
In a preferred configuration the contact surface is constituted by a
transparent
contact element which is part of a patient adapter which is coupled, in
particular
exchangeably coupled, with a focusing objective of the apparatus.
According to a further aspect, in accordance with the invention a method for
controlling a focal point of a treatment laser beam for ophthalmological laser
surgery
is furthermore provided, comprising the following steps:
- directing a treatment laser beam onto a focal point by means of an
imaging system,
- measuring a temperature assigned to the imaging system, and
- controlling the focal-point setting in a manner depending on the measured
temperature.
The method may further comprise the steps of establishing a shaping abutting
contact between an eye and a contact surface, and of directing the treatment
laser
beam through the contact surface onto the eye.
Also in connection with the method aspect, measured position data that are
representative of a measured position of the contact surface at at least one
place in
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the same relative to the direction of propagation of the treatment laser beam
can be
ascertained or read out, as described previously. Irrespective of whether the
measured position data were ascertained or read out, the focal point can be
preset in
a manner depending on the measured position data and, subsequent to this, can
be
readjusted on the basis of the measured temperature.
The invention will be elucidated further in the following on the basis of the
appended
drawings. Shown are:
Fig. 1 in greatly schematised manner, a first exemplary embodiment of an
apparatus for ophthalmological laser surgery; and
Fig. 2 in greatly schematised manner, a second exemplary embodiment of
an
apparatus for ophthalmological laser surgery.
The laser-surgical apparatus according to both embodiments is generally
denoted by
10.
The laser-surgical apparatus 10 according to the first embodiment has a
femtosecond
zo laser (fs laser) 12 which emits pulsed laser radiation with pulse
durations within the
femtosecond range. The laser radiation propagates along an optical beam path
14
and finally arrives at an eye 16 to be treated. In the beam path 14 various
components for guiding and shaping the laser radiation are arranged. In
particular,
these components include a focusing objective 18 (for example, an f-theta
objective)
and also a scanner 20 connected upstream of the objective 18, by means of
which
the laser radiation provided by the laser 12 is capable of being deflected in
a plane
(x-y plane) orthogonal to the beam path 14. A coordinate system that has been
sketched in illustrates this plane and also a z-axis defined by the direction
of the
beam path 14. The scanner 20 is, for example, constructed in a manner known as
such from a pair of galvanometrically controlled deflecting mirrors which are
each
responsible for the beam deflection in the direction of one of the axes
spanning the
x-y plane. A central control unit 22 controls the scanner 20 in accordance
with a
control program stored in a memory 24, which implements an incision profile
(represented by a three-dimensional pattern of scan points at which, in each
instance, a photodisruption is to be brought about) to be generated in the eye
16.
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Moreover, the aforementioned components for guiding and shaping the laser
radiation include at least one controllable optical element 26 for z-
adjustment of the
beam focus of the laser radiation. In the exemplary case that is shown, this
optical
element is constituted by a lens. A suitable actuator 28, which in turn is
controlled
by the control unit 22, serves for controlling the lens 26. For example, the
lens 26
may be mechanically displaceable along the optical beam path 14.
Alternatively, it is
conceivable to use a controllable liquid lens of variable refractive power.
With
unchanged z-position and also otherwise unchanged setting of the focusing
objective
18, by displacing a longitudinally adjustable lens or by variation of the
refractive
power of a liquid lens it is possible to obtain a z-shift of the beam focus.
It will be
understood that for the purpose of z-adjustment of the beam focus other
components are also conceivable, for instance a deformable mirror. On account
of
its comparatively greater inertia, with the focusing objective 18 it is
expedient to
undertake only an initial basic setting of the beam focus (i.e. focusing to a
predetermined z-reference position) and to effect the z-shifts of the beam
focus
which are predetermined by the incision profile by means of a component with
quicker speed of response which is arranged outside the focusing objective 18.
It
will be understood that the lens 26 may also be part of the scanner 20, and
the
scanner 20 formed thereby may be arranged both upstream of and downstream of
the semitransmitting deflecting mirror 40. The case in which the lens is part
of the
scanner 20 and this scanner 20 containing the lens 26 is arranged upstream of
the
deflecting mirror 42 will be elucidated later with reference to Figure 2.
On the side of emergence of the beam the focusing objective 18 is coupled with
a
patient adapter 30 which serves for establishing a mechanical coupling between
the
eye 16 and the focusing objective 18. Ordinarily in the course of treatments
of the
type being considered here a suction ring which is not represented in any
detail in
the drawing but which is known in itself is placed onto the eye and fixed
there by
suction force. The suction ring and the patient adapter 30 form a defined
mechanical
interface which permits a coupling of the patient adapter 30 onto the suction
ring. In
this regard, reference may be made, for example, to international patent
publication No.
WO 2010/022745 Al.
The patient adapter 30 serves as carrier for a transparent contact element 32
which,
in the exemplary case that is shown, takes the form of a plane-parallel
applanation
plate. The patient adapter 30 comprises, for example, a taper-sleeve body, at
the
narrower (in the drawing, lower) sleeve end of which the applanation plate 32
is
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arranged. In the region of the wider (in the drawing, upper) sleeve end the
patent
adapter 30 is, on the other hand, attached to the focusing objective 18 and
possesses there suitable structures which permit a fixing, if desired a
detachable
fixing, of the patient adapter 30 to the focusing objective 18.
Because it comes into contact with the eye 16 during the treatment, the
applanation
plate 32 is a critical article from the point of view of hygiene, which
therefore is
expediently to be exchanged after each treatment. For this purpose the
applanation
plate 32 may have been exchangeably fitted to the patient adapter 30.
Alternatively,
lo the patient adapter 30 may form, together with the applanation plate 32,
a
disposable unit, for which purpose the applanation plate 32 may have been
undetachably connected to the patient adapter 30.
In any case, the underside of the applanation plate 32, facing towards the
eye, forms
a plane contact surface 34 against which the eye 16 is pressed in preparation
for the
treatment. This brings about a levelling of the anterior surface of the eye,
with
simultaneous deformation of the cornea, denoted by 36, of the eye 16.
In order to be able to utilise the contact surface 34 as a reference for the
presetting
zo of the beam focus in the z-direction, it is necessary to know its z-
position in the
coordinate system of the laser-surgical apparatus. By reason of unavoidable
manufacturing tolerances, it cannot be ruled out that in the case of
incorporation of
varying applanation plates or varying patient adapters 30, which are each
equipped
with an applanation plate 32, the z-position and, under certain circumstances,
also
the angular position of the contact surface 34 show more or less significant
fluctuations. To the extent that these fluctuations remain disregarded in the
z-
presetting of the beam focus, undesirable errors arise in the actual position
of the
incisions in the eye 16 that are produced.
The laser-surgical apparatus 10 therefore includes an optical-coherence
interferometric measuring device 38, for example an OLCR measuring device
(OLCR:
optical low-coherence reflectometry), which emits a measuring beam which by
means of an immovably arranged semitransmitting deflecting mirror 40 is
coupled
into the beam path 14 in which the treatment laser radiation of the laser 12
also
travels. The measuring device 38 causes the generated measuring beam to
produce
interference with a reflection beam coming back from the eye 16. From the
measured interference data acquired in this regard, the z-position of the
contact
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surface 34 within the coordinate system of the laser-surgical apparatus can be
ascertained. Therefore the measured interference data may also be designated
as
measured position data. The control unit 22 receives the measured interference
data
from the measuring device 38 and calculates therefrom the z-position of that
place
on the contact surface 34 at which the measuring beam impinged or through
which
the measuring beam passed.
In the exemplary case that is shown, the measuring beam emitted by the
measuring
device 38 passes through the scanner 20. This makes it possible to utilise the
deflecting function of the scanner 20 also for the measuring beam. The scanner
module 20 could also contain a second separate scanner solely for the OLCR,
which,
equipped with smaller mirrors, operates distinctly more quickly.
In the course of the following laser treatment of the eye 16 the control unit
22 takes
into account the actual z-position of the contact surface 34 ascertained in
this way in
connection with the z-control of the beam focus, specifically in such a way
that the
incision is in fact produced at the intended position deep within the cornea
36. For
this purpose the evaluating and control unit 22 references the z-position of
the beam
focus that is to be set to the measured z-position of the contact surface 34.
By virtue of the previously described procedure, the z-position of the beam
focus is,
however, only preset, since temperature drifts of the effective focal length
of the
laser-surgical apparatus 10 and also of the real optical length of the patient
adapter
in the z-direction are not taken into account. Accordingly, the laser-surgical
25 device 10 has four temperature sensors 50, 52, 54, 56, two of which are
arranged on
the scanner 20, and two of which are arranged on the focusing objective 18.
The
temperature sensors measure the real temperature at their corresponding
positions
and relay the measured temperature values to the control unit 22. Relaying of
the
temperature values to the control unit 22 may be effected in wireless or wired
30 manner; i.e. the temperature sensors 50 52, 54, 56 may be connected to
the control
unit 22 in wireless or wired manner. In the exemplary embodiment represented
in
Figure 1, in exemplary manner the scanner 20 and hence the temperature sensors
50, 52 arranged on the scanner 20 are connected to the control unit 22 in
wired
manner, whereas the temperature sensors 54, 56 arranged on the focusing
objective
18 are connected to the control unit 22 in wireless manner in order to relay
their
measured temperature values to the control unit 22 for further processing.
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In the memory 24 a temperature sensitivity of the effective focal length is
saved as a
family of curves, both for the scanner 20 and for the focusing objective 18.
Given
the existence of a new measured temperature value, the control unit evaluates
the
associated function and generates a corresponding actuating variable for the
purpose
of readjusting the preset z-position of the lens 26. Once a temperature value
is
ascertained by one or both of the temperature sensors 50, 52 fitted to the
scanner
20 (in the case of the measurement of two temperature values by the two
temperature sensors 50, 52, an average temperature value derived from the two
values is used), the temperature sensor relays the measured temperature value
to
lo the control unit 22. The latter then searches the memory 20 for the
associated
temperature sensitivity for the scanner 20, generates therefrom an actuating
variable
and communicates the latter to the actuator 28 which shifts the lens 26 in the
z-
direction in accordance with the actuating variable. By virtue of this z-shift
of the
lens 26, the preset position of the beam focus is readjusted in such a manner
that
changes in the real optical length of the patient adapter and/or changes in
the
effective focal length of the laser-surgical apparatus 10, occurring by reason
of
fluctuations in the real temperature, are also taken into account and
compensated.
According to the second embodiment of the laser-surgical apparatus 10 shown in
Figure 2, the scanner 20 comprises the lens 26 which is positionally shiftable
in the
direction of propagation of the treatment laser beam and is arranged upstream
of the
deflecting mirror 42 in the direction of propagation of the laser radiation.
In this
manner the scanner 20 is a 3D scanner which possesses three-dimensional scan
properties, so that the laser radiation can be deflected in any direction (x,
y, z) by
the 3D scanner 20.
Recording and evaluation of the measured temperature values by means of the
temperature sensors 50, 52, 54, 56 and the control unit 22 are effected in a
manner
analogous to the first embodiment shown in Figure 1. As distinct from the
first
embodiment, in the second embodiment shown in Figure 2 both the presetting of
the
focal point and the readjustment of the focal point are effected by the 3D
scanner 20
which is controlled by the control unit 22.
