Note: Descriptions are shown in the official language in which they were submitted.
1OA-116 079
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Device for the laser radiation treatment of an eye
The invention relates to an apparatus for treating an eye with laser
radiation.
In refractive ophthalmological surgery the refractive properties and imaging
proper-
ties of the eye are changed by interventions in respect of the eye of a
patient for the
purpose of correcting or alleviating sight defects. Known, in particular, is
the LASIK
process, wherein the cornea of the eye is reshaped. In the conventional LASIK
proc-
ess, in a first step a flat corneal incision is made with a mechanical
microkeratome, in
order in this way to produce a so-called flap which remains firmly connected
to the
cornea on one side, so that it can be folded upwards in order to expose
underlying
corneal tissue (stroma). In the exposed stroma the so-called ablation - that
is to
say, the removal of tissue by means of, ordinarily, excimer-laser radiation -
is then
carried out, whereupon the flap is then folded back and heals up. In this
process the
epithelium remains largely uninjured and the healing process takes place
relatively
quickly and in pain-free manner. In a conventional mechanical microkeratome a
sharp blade oscillates.
For the purpose of cutting the flap, the mechanical microkeratome has recently
been
increasingly replaced by laser radiation. The laser radiation is focused below
the
surface of the cornea and guided on a trajectory, the power densities being so
high
that a continuous incision arises by virtue of photodisruptive effects. In
order to
obtain the high power densities, extremely short laser pulses within the
femtosecond
range are employed, for which reason this process is also designated as fs
LASIK.
The present invention relates, in particular, to this fs LASIK but, above and
beyond
this, also to any other process for treating an eye with laser radiation,
wherein the
radiation is also guided in space and time in relation to the eye in
accordance with a
so-called treatment program. It will be understood that this control of the
laser ra-
diation in space and time has to be effected in relation to a precisely
defined and
reproducible reference-point of the eye. By way of such a reference-point, as
a
general rule a so-called centre of the eye is chosen - that is to say, a point
situated
centrally - which serves as reference for the local guidance of the laser
radiation over
the eye. Since, in the processes under discussion here, as a general rule the
laser
radiation is focused to small spots, the locations of each spot are
accordingly aligned
1OA-116 079
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in relation to the stated centre as reference-point. The present invention
relates, in
particular, to fs LASIK but also to other eye treatments in which laser
radiation has to
be positioned in precisely defined manner in relation to the eye, such as, for
in-
stance, in the case of keratoplasty (e.g. anterior or posterior lamellar
keratoplasty,
perforating keratoplasty in the case of corneal transplants), fs lenticle
extraction for
the purpose of refractive correction, the cutting of intercorneal annular
segments for
the purpose of stabilising keratoconus and projection of the cornea, cataract
inci-
sions, presbyopia incision in the crystalline lens, intrastromal inlays,
keratomy in the
case of astigmatism, corneal resection etc.
In the state of the art, the centring of the surgical treatment location is
ordinarily
effected by adjustment of the so-called applicator, such as a suction ring,
which on
one side is connected to the eye by suction and on the other side exhibits a
socket
onto which focusing optics are capable of being coupled, with which the laser
radia-
tion is focused onto or into the cornea. In this process the surgeon performs
the
positioning of the applicator (suction ring) on the eye 'by eye', where
appropriate
utilising optical magnifying devices. The surgeon tries to place the
applicator as
centrically as possible in relation to certain contours of the eye. The
guiding-point
for this centring by eye may be, for example, the pupil or the iris. However,
in this
state of the art the optimal positioning and centring of the applicator, and
hence of
the surgical treatment location, relative to the eye depends greatly on the
subjective
capabilities of the surgeon. In other words: suboptimal conditions may arise
in the
course of this conventional positioning of the applicator.
The object underlying the invention is to make available an apparatus for
treating an
eye with laser radiation, wherein the radiation is controlled in space and
time in rela-
tion to the eye in accordance with a treatment program in such a manner that a
precise and reliably reproducible reference-point is available for the control
of the
laser radiation.
An apparatus according to the invention for achieving this object exhibits the
follow-
ing:
A laser radiation source for generating laser radiation, means for directing
the laser
radiation onto the eye for the purpose of an ophthalmological intervention on
or in
the eye, a controller for controlling the laser radiation in space and time in
relation to
the eye in accordance with a treatment program which is oriented towards a
centre
1OA-116 079
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of the eye, a camera which records a feature of the eye, and an image-
processing
unit which derives information about the centre of the eye from the recording
of the
camera and enters this information into the controller, as a result of which
the con-
troller controls the laser radiation in accordance with the treatment program
and in a
manner depending on the derived centre of the eye.
Hence the invention enables an exact centring of the surgical treatment in
relation to
the target tissue (cornea). For this purpose a camera system is employed which
on
the basis of an eye feature - i.e. a specified anatomical structure of the eye
- auto-
matically recognises the treatment location by means of image processing -
i.e.
without influence of subjective influences having their origin in the
respective sur-
geon. Suitable features for image processing for the purpose of ascertaining a
refer-
ence-point, in particular a centre for the treatment, are geometrical
structures of the
eye from which a centre can be derived (ascertained) automatically by image
proc-
essing, such as, for example, the pupil, the middle of which can be defined as
centre,
the iris structure or even the limbal structure. Alternatively or in addition,
in the rear
portion of the eye the structure of the retina can also be registered, and
assertions
concerning a reference-point for the laser treatment can be derived from the
ar-
rangement of blood vessels in the retinal region and/or from the orientation
of the
fovea relative to the pupil.
A special configuration of the invention has reference to the applicator
introduced
above - that is to say, for example, a suction ring. Such suction-ring
techniques are
described, for example, in US 5,549,632, WO 03/002008 Al and
PCT/EP2008/006962. If the invention is employed together with an applicator,
the
camera is set up to record the applicator and at least one
geometrical/structural
feature of the eye, whereupon from this recording relating to both the
applicator and
the structure of the eye the image-processing unit derives a local
relationship be-
tween the position of the applicator in relation to the eye and emits a
corresponding
signal to the laser controller, whereupon the controller then controls the
laser radia-
tion in relation to the eye in a manner depending on this signal. This means
that a
possible suboptimal positioning of the applicator in relation to the eye is
compen-
sated by computation in the course of control of the laser radiation - that is
to say,
for example, when the control program for the control of the laser radiation
in accor-
dance with a certain treatment program is firstly oriented towards the centre
of the
applicator but by virtue of the image processing it is established that the
applicator is
not optimally positioned centrically in relation to the eye, subsequently the
treatment
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program is no longer oriented towards the centre of the applicator but rather
towards
the centre of the eye actually ascertained by the image processing.
Alternatively, in accordance with the invention the camera with the image-
processing
program can also be employed in such a way that when the middle of the
applicator
does not coincide ideally with the desired reference-point for the laser
treatment
(that is to say, for example, with the centre of the pupil), assistance is
given to the
surgeon as to how the applicator is best repositioned on the eye in such a way
that
the reference-point comes to be situated on the central axis of the
applicator. Then
the surgeon can firstly detach the applicator and then reattach it in
accordance with
this datum. In a fully mechanised system, this detachment and reattachment of
the
applicator may also occur in fully mechanical manner.
The invention is particularly suited for use in the case of the fs LASIK
elucidated
above for cutting the flap in such a manner that the geometry and positioning
of the
flap incision are precisely aligned with a reference-point on the eye in such
a way
that after the flap has been folded upwards a region of the stroma is
available that is
as large as possible and optimally situated in order to carry out the desired
ablation.
Exemplary embodiments of the invention will be elucidated in more detail in
the
following on the basis of the drawing. Shown are:
Fig. 1 schematically, an exemplary embodiment of an apparatus for treating an
eye with laser radiation;
Fig. 2 schematically, the top view of an eye and the positioning of a flap
incision
for fs LASIK;
Fig. 3 a schematic view corresponding to Fig. 2, wherein the flap incision is
op-
timally positioned; and
Fig. 4 another situation with optimised flap incision.
In Fig. 1 the eye to be treated with laser radiation is represented
schematically by
reference symbol 10. In this exemplary embodiment a laser 12 serves for the
gen-
eration of femtosecond pulses. The laser radiation 14 is directed towards the
eye 10
via means described in more detail further below.
1OA-116 079
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With a suction ring 16, known as such, the eye is fixed, and on the central
axis 18 of
the suction ring 16 an applanation lens 20 is introduced into a socket of the
suction
ring - i.e. lowered downward from the position shown in Figure 1. In the
process,
an interface unit 22 couples focusing optics 24 onto the suction ring 16. The
focus-
ing optics 24 are guided in a mount 26. Guidance is effected by means of a
location
sensor 28, the focusing optics 24 being suspended in feely floating manner via
a
counterweight 30 and a rope/pulley arrangement or a swivel joint, in order to
enable
a coupling of the interface unit with the focusing optics 24 onto the eye 10
in a man-
ner that places virtually no burden on the eye.
The suction ring 16 is fixed by means of pipe connections 34, 36, known as
such,
and vacuum pumps 38.
The laser radiation 14 generated by the laser 12 is directed into the focusing
optics
24 via mirrors 40, 42, 44 which are known as such. A computer controller 50
con-
trols all the controllable components of the system, the control connections
being
indicated in Fig. 1 by dashed lines. In a memory 54 a control program is
stored - i.e.
a treatment program for the control of the laser radiation 14' in space and
time in
relation to the eye 10.
A camera 46 is arranged above a mirror 44 which is transmitting in respect of
radia-
tion coming from the eye 10, so that geometrical structures on the eye 10 can
be
recorded digitally with the camera 46, for example a CCD/CMOS camera. In the
computer controller 50 an image-processing unit 50a is located which processes
images supplied by the camera 46, in order to derive from a specified
geometrical
structure of the eye - such as the pupil, for example - a reference-point, in
particular
a centre, in accordance with which the controller 50 executes the treatment
program
52. The arrangement according to Fig. 1 is elucidated in more detail in
international
patent application PCT/EP2008/006962, which is included here in full by
reference.
Figures 2, 3 and 4 show schematically, in a top view of an eye 10, details of
the
image processing with the camera 46 and with the image-processing unit 50a.
Figures 2, 3 and 4 show schematically the periphery 60 of the optically useful
surface
of the cornea. The pupil is marked by reference symbol 62. 64 denotes the
periph-
ery of a possible flap incision - that is to say, the hatched region in the
Figures.
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Reference symbol 66 marks with a dashed line the ablation region - that is to
say,
that region of the cornea in which corneal tissue in the stroma is to be
ablated after
the flap has been folded back (according to the periphery 64). As described in
the
introduction, the flap has a region of connection to the cornea that is not
cut, ordi-
narily designated as a hinge, this being marked in the Figures by reference
symbol
68.
According to Fig. 2, the pupil 62 has a centre Z. The hinge region 68 for the
flap
cannot be used for the laser ablation, so that with concentric arrangement of
the flap
periphery 64 in relation to the pupil 62 a suboptimal region for the ablation
arises.
By virtue of the hinge 68, distance a according to Fig. 2 is greater than
distance don
the side of the cornea situated opposite the hinge 68. The spacing b between
the
hinge 68 and the pupil 62 on the hinge side is also smaller than the
corresponding
spacing con the opposite side, as is indicated in Fig. 2.
In the exemplary embodiment that is represented, the camera 46 records the
pupil
62 and derives from this feature the position of the centre Z of the pupil in
accor-
dance with an algorithm that is known as such, for instance in a manner
analogous
to a so-called centre-of-gravity derivation in the case of a pupil shape that
is not
totally circular. The image-processing unit 50a in the control computer 50 now
proc-
esses the recording of the image in such a way that a maximal ablation zone 66
is
obtained, in that, according to Fig. 3, spacing a defined therein becomes
equal to
spacing d, and analogously spacing b becomes equal to spacing c, these
spacings, as
represented graphically, always being measured perpendicular to the edge of
the
hinge 68. Consequently a flap periphery 64 arises which is not precisely
centric in
relation to the pupillary centre Z. Accordingly, for the purpose of obtaining
a maxi-
mal ablation zone the periphery 64 for the flap incision is offset in relation
to the
pupillary centre Z, and with the aid of the camera 46 and the image-processing
unit
50a the treatment program for controlling the laser radiation 14 for producing
the
flap incision is automatically offset geometrically in relation to the
reference-point Z
in such a way that the spacings a, b, c, dthat are drawn in Fig. 3 at least
approxi-
mately satisfy the stated equality relations.
Fig. 4 shows schematically a somewhat extreme situation in the case of a
patient's
eye with greatly offset pupil 62 in relation to the midpoint of the optically
useful
surface 60. Also in this exemplary embodiment the flap periphery 64 is not
chosen
to be concentric in relation to the pupillary centre Z, but rather the centre
of the flap
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periphery 64 is offset in relation to the centre Z of the pupil in a direction
perpen-
dicular to the edge of the hinge 68, whereby a restriction obtains with
respect to the
maximum possible diameter of the flap by virtue of the fact that the diameter
of the
flap can only be produced within the optically useful surface 60.
The exemplary embodiments show an objective, i.e. automated, positioning of
the
ablation region 66.
