Note: Descriptions are shown in the official language in which they were submitted.
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Device for cutting the human cornea
The invention is concerned with the generation of incisions in the human
cornea
by means of focused laser radiation. In particular, the invention is concerned
with the preparation of a LASIK flap by means of such laser radiation.
A frequently employed technique for eliminating visual defects of the human
eye
- such as, for example, myopia or hyperopia or astigmatism - is so-called
LASIK.
LASIK stands for laser in-situ keratomileusis and designates a technique in
which
firstly a small cover disc in the cornea is cut free which is folded aside in
order to
expose the underlying tissue regions of the cornea. These exposed tissue
regions are then treated in ablating manner by means of focused UV laser
radiation ¨ i.e. corneal material is removed in accordance with an ablation
profile
ascertained individually for the patient. The small cover disc is usually
designated in specialist circles as a flap and is not severed completely from
the
remaining tissue of the cornea but is still connected to the rest of corneal
tissue
in a hinge region which in specialist circles is generally designated as a
hinge.
This enables a simple folding-away of the flap and, above all, a simple
folding-
back of the flap after the ablation. On account of the removal of material, a
changed shape of the anterior surface of the cornea arises after the flap has
been folded back. The associated result of this is a different refractive
behaviour
of the cornea and consequently of the overall system constituted by the eye.
By
suitable definition of the ablation profile it can be ensured that the visual
defect
is at least distinctly attenuated and, at best, is almost completely
eliminated.
Various procedures for the preparation of the flap are known in the state of
the
art. One procedure uses a mechanical microkeratome ¨ i.e. a microsurgical
scalpel which cuts into the cornea with a cutting blade which is ordinarily
driven
in oscillating manner. Another procedure, which will be considered in more
detail within the scope of the invention, uses focused short-pulse laser
radiation
for the purpose of preparing the flap. In this case, laser radiation with
pulse
durations within the femtosecond range, for example within the low three-digit
femtosecond range, is ordinarily employed. In addition, the laser radiation
usually has a wavelength above about 300 nm, in order to enable a coupling of
the radiant energy deep into the corneal tissue. LASIK treatments in which the
flap is prepared by means of such short-pulse laser radiation are often
designated as fs LASIK.
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For the generation of incisions by means of focused laser radiation in
transparent material (transparent to the laser radiation), the so-called laser-
induced optical breakthrough is utilised as a physical effect. This
breakthrough
ultimately results in a photodisruption of the irradiated tissue in the region
of the
focus. The laser radiation that is beamed in brings about a local vaporisation
of
the irradiated material at the focal point. In the process, gases arise which
¨ to
the extent that they are not conducted away to the outside ¨ collect in
internal
cavities or are absorbed by the adjoining material. It has been found that in
the
course of LASIK treatments of the human eye a residence in the cornea of the
gases arising in the course of preparation of the flap can lead to problems in
the
course of the subsequent laser ablation. In particular, it has been found that
these gases can render difficult a precise tracking of the eye by means of an
eye-tracker. Laser systems that are employed for the ablation of corneal
tissue
frequently possess such an eye-tracker, in order to register eye movements
during the laser treatment and to reposition the laser radiation
correspondingly.
As a rule, the eye-trackers are constructed from a camera and suitable image-
evaluation software which evaluates the images recorded by the camera and
detects changes in the position of the eye. Frequently the image-evaluation
software evaluates characteristic features of the eye - for instance, defined
points of the iris or/and the pupillary centre or/and the corneal apex or/and
the
limbus. It has been shown that accumulations of gas remaining in the cornea,
which have arisen in the course of preparation of the flap, can impede the
acquisition of such characteristic features of the eye. It goes without saying
that
for the success of the operation a precise functioning of the eye-tracker is
absolutely essential.
The object of the invention is to demonstrate a way in which, in the case of
LASIK treatments, an impairment of the success of the operation by troublesome
accumulations of gas which arise in the course of a preparation of the LASIK
flap
by laser can be avoided.
With a view to achieving this object, the invention proposes a device for
cutting
the human cornea with focused pulsed laser radiation. The device includes
controllable components for local setting of the beam focus, a control
computer
for controlling these components, and a control program for the control
computer. The control program contains instructions that upon execution by the
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control computer are designed to bring about the generation of an incision
figure
in the cornea encompassing the flap incision, whereby according to the
invention
the incision figure further encompasses an auxiliary incision connected with
the
flap incision and leading locally as far as the surface of the cornea. The
auxiliary
incision establishes a connection between the flap incision and the surface of
the
cornea. In this way, gases arising surgically are able to escape to the
surface of
the cornea and hence out of the corneal tissue. A penetration of these gases
into critical tissue regions of the eye can be avoided in this way. Any
impairments of an eye-tracker can also be avoided better in the course of the
lo following laser ablation.
The above reference to a local progression of the auxiliary incision is
intended to
serve to avoid confusions with the temporal progression in the course of
generation of the auxiliary incision. A statement about a defined local
progression of an incision or of a part of an incision is not intended here
generally to imply any assertion whatsoever about the temporal sequence in the
course of generation of the incision. Accordingly, an incision for which the
assertion is made that it proceeds locally from a defined first location to a
defined second location may easily be generated temporally in the direction
from
the second location to the first location.
In a preferred configuration the auxiliary incision begins locally directly
from the
flap incision and proceeds locally away from the latter as far as the surface
of
the cornea. Though it is also conceivable that one or more gas pockets or gas
cavities within the corneal tissue adjoining the first incision are firstly
generated
surgically, and that the auxiliary incision leads from these gas pockets or
gas
cavities locally to the surface of the cornea.
The auxiliary incision preferably forms a planar and, if desired,
substantially flat
channel, in which connection the length, width and gradient angle of the
channel
can be chosen variably. The channel may have substantially constant width over
its length; though generating a channel of varying width is not to be
excluded.
For the generation of the auxiliary incision, it may be sufficient to produce
photodisruptions alongside one another in a single plane only. Though
producing such photodisruptions also in two or more planes above one another
is not to be excluded if a larger cross-section of the channel is desired.
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In a preferred configuration the auxiliary incision is connected with the flap
incision in a hinge region of the flap formed by the flap incision, and
extends on
the other side of the flap locally to the surface of the cornea. If desired,
in this
case the auxiliary incision is narrower than the hinge region.
For an optimal removal of photodisruption gases arising (i.e. gases that arise
in
the course of and as a consequence of the photodisruption), it is advisable
that
the auxiliary incision has greatest corneal depth in a region in which it is
connected with the flap incision, and proceeds locally, beginning from this
region, with increasingly smaller corneal depth as far as the surface of the
cornea.
It is favourable if the instructions of the control program are designed to
generate the auxiliary incision before the flap incision is produced. This
creates
the prerequisite for a gas-removal channel to be available right from the
start,
via which the photodisruption gases arising in the course of preparation of
the
flap can be conducted away.
In advantageous manner the instructions of the control program are designed to
generate at least a predominant part and preferably the largest part of the
auxiliary incision in a direction from the surface of the cornea to the flap
incision.
The formation of photodisruption gases has to be reckoned with also in the
course of generation of the auxiliary incision. Insofar as the auxiliary
incision is
generated in the direction away from the surface of the cornea, it is possible
to
conduct these photodisruption gases away optimally. For example, the
instructions of the control program may be designed to generate at least a
predominant part of the auxiliary incision with line scans of the beam focus
that
progress, line by line, along a direction of extension of the auxiliary
incision that
proceeds from the surface of the cornea to the flap incision. Though it is
just as
possible that the instructions of the control program are designed to generate
at
least a predominant part of the auxiliary incision with line scans of the beam
focus that progress, line by line, transverse to a direction of extension of
the
auxiliary incision that proceeds from the surface of the cornea to the flap
incision.
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The flap incision may encompass a bed incision completely situated deep within
the corneal material, preferentially at substantially constant depth, as well
as a
lateral incision adjoining the bed incision and guided out locally to the
surface of
the cornea. The bed incision is so designated because it defines the stromal
bed
for the flap. Given prior applanation (levelling) of the surface of the cornea
by
abutment against a suitable applanation face, the bed incision may be
realised,
for example, by a flat surface incision which is inserted at constant depth of
the
cornea. In principle, it is conceivable to generate the bed incision with line
scans or with spiral scans of the radiation focus. However, for an optimal
io removal of the photodisruption gases arising in the course of generation
of the
bed incision it is proposed that the instructions of the control program are
designed to generate the bed incision with line scans of the radiation focus
that
progress increasingly, line by line, in the direction away from a hinge region
of
the flap. At the same time, the instructions of the control program are
expediently designed to generate the lateral incision temporally after the bed
incision. Since the lateral incision leads locally out to the surface of the
cornea,
it is advisable to generate the lateral incision, beginning from its most low-
lying
regions, in a direction towards the surface of the cornea. Of course, an
opposite
direction in the course of generation of the lateral incision is equally
conceivable.
For a good transition, sufficiently permeable to the photodisruption gases,
between the auxiliary incision and the flap incision, it is advisable that the
instructions of the control program are designed to bring about, in a
transition
region between auxiliary incision and flap incision, line scans of the beam
focus
that progress, line by line, transverse to the transition direction. Equally,
for a
good opening of the auxiliary incision outwards, it is advisable that the
instructions of the control program are designed to bring about, in the
surface-
side end region of the auxiliary incision (by 'end region' here a local end
region
is meant; the surface-side end region may perfectly well be the starting
region in
connection with the generation of the auxiliary incision), line scans of the
radiation focus that progress, line by line, transverse to the direction of
entry of
the auxiliary incision into the cornea.
In a further development of the invention the device may further include a
contact element that is transparent to the laser radiation, with a contact
face
intended for abutment against the eye, the instructions of the control program
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being designed to generate the auxiliary incision in such a way that its end
opening out on the surface of the cornea lies in a region of the cornea in
which
the latter bears against the contact face of the contact element.
In a first configuration the contact face may exhibit a plane surface portion
for
levelling a part of the surface of the cornea, the instructions of the control
program being designed to generate the auxiliary incision in such a way that
its
end opening out on the surface of the cornea lies in a region of the cornea in
which the latter bears against the plane surface portion of the contact face.
In an alternative configuration the contact face may exhibit a plane surface
portion for levelling a part of the surface of the cornea, as well as a
surface
portion adjoining the plane surface portion and proceeding obliquely relative
to
the latter in the direction towards the side of the contact element facing
away
from the eye, the instructions of the control program being designed to
generate
the auxiliary incision in such a way that its end opening out on the surface
of the
cornea lies in a region of the cornea in which the latter bears against the
obliquely proceeding surface portion of the contact face. The obliquely
proceeding surface portion is preferentially of rounded construction and
adjoins
the plane surface portion in kink-free manner.
According to another further embodiment the device may include a contact
element that is transparent to the laser radiation, with a contact face
intended
for abutment against the eye, the instructions of the control program being
designed to generate the auxiliary incision in such a way that its end opening
out on the surface of the cornea lies outside a region of the cornea in which
the
latter bears against the contact face of the contact element.
In this further embodiment, for the purpose of adapting the refractive index a
chamber is preferentially provided on the side of the contact element facing
towards the eye, which via a filling-channel arrangement is capable of being
filled with a liquid or with another suitable flowable medium which reduces
the
jump in refractive index from the contact element to the cornea and
expediently
possesses optically homogeneous properties. Instead of being present in liquid
form, this medium may also be present, for example, in gel-like form. Also not
excluded is the use of a gaseous medium. The instructions of the control
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program are in this case designed to generate the auxiliary incision in such a
way that it leads into the liquid-filled chamber (or, generally, into the
chamber
filled with the medium).
In the case of formation of the flap incision with a flat bed incision, the
instructions of the control program are preferentially designed to generate
the
auxiliary incision opening out into the chamber and the bed incision in a
common plane. This relates to the flattened case - that is to say, the state
in
which the eye is bearing against the contact element.
A process for treating the human eye includes the following steps: providing
first
pulsed laser radiation, the laser radiation having a radiation focus,
directing the
first laser radiation onto a human cornea to be treated, controlling the
radiation
focus of the first laser radiation for the purpose of generating a flap
incision in
the cornea forming a flap, as well as an auxiliary incision connected with the
flap
incision and leading locally as far as the surface of the cornea.
The process may further include the following steps: folding the flap away, in
order thereby to expose underlying corneal tissue, providing second pulsed
laser
radiation, directing the second laser radiation onto the exposed corneal
tissue,
and ablating the exposed corneal tissue with the second laser radiation in
accordance with a predetermined ablation profile.
The first laser radiation preferentially has pulse durations within the
femtosecond range and has a wavelength above 300 nm. The second laser
radiation has a wavelength within the UV range and may, for example, be
generated by an excimer laser, for instance by an ArF excimer laser radiating
at
193 nm.
The invention will be elucidated further in the following on the basis of the
appended drawings. Represented are:
Figure 1 in schematic block representation, an exemplary embodiment of a
laser arrangement for inserting intracorneal incisions,
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Figures 2a and 2b two variants of a corneal incision figure for preparing a
LASIK flap,
Figure 3 the incision figure shown in Figure 2a, in a cross-sectional view,
Figure 4 an exemplary scan pattern of a laser beam that is used for generating
the incision figure shown in Figure 2a,
Figures 5 and 6 two variants for generating a flap incision,
supplemented
by an auxiliary incision, in a flattened cornea.
The laser arrangement shown in Figure 1 ¨ denoted generally by 10 ¨ includes a
laser source 12 which generates a laser beam 14 with pulse durations within
the
femtosecond range. In the beam path of the laser beam 14 a series of
components are arranged, inter alia a scanner 16, indicated here schematically
as a unitary functional block, an immovable deflecting mirror 17 and also a
focusing objective 18. The scanner 16 serves for transverse and longitudinal
local control of the focal point of the laser beam 14. 'Transverse' here
designates a direction at right angles to the direction of propagation of the
laser
beam 14; 'longitudinal' corresponds to the direction of beam propagation. In
conventional notation the transverse plane is designated as the x-y plane,
whereas the longitudinal direction is designated as the z-direction. For the
purpose of transverse deflection of the laser beam 14 (i.e. in the x-y plane)
the
scanner 16 may, for example, include a pair of galvanometrically actuated
scanner mirrors which are capable of being tilted about mutually perpendicular
axes. Alternatively, for example, a transverse deflection by means of an
electro-
optical crystal is conceivable. For the z-control of the position of the focus
the
scanner 16 may contain, for example, a longitudinally adjustable lens or a
lens
of variable refractive power or a deformable mirror, with which the divergence
of
the laser beam 14 and consequently the z-position of the beam focus can be
influenced. It will be understood that the components of the scanner 16
serving
for the transverse focus control and for the longitudinal focus control may be
arranged distributed along the beam path of the laser beam 14 and, in
particular, apportioned to different modular units. For example, the function
of
the z-focus control may be fulfilled by a lens arranged in beam-expanding
optics
(beam expander, e.g. Galilean telescope), whereas the components serving for
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the transverse focus control may be accommodated in a separate modular unit
between the beam-expanding optics and the focusing objective 18. The
representation of the scanner 16 as a unitary functional block in Figure 1
serves
merely for better clarity of layout.
The focusing objective 18 is preferably an f-theta objective and is
preferentially
separably coupled on its beam-emergence side with a patient adapter 20 which
forms an abutment interface for the cornea of an eye 22 to be treated. For
this
purpose the patient adapter 20 exhibits a contact element 24 that is
transparent
to the laser radiation and that on its underside facing towards the eye
exhibits a
abutment face (contact face) 26 for the cornea. In the exemplary case that is
shown, the abutment face 26 is constructed as a plane face and serves for
levelling the cornea, by the contact element 24 being pressed against the eye
22
with appropriate pressure or by the cornea being aspirated onto the contact
face
26 by reduced pressure. The contact element 24 (in the case of plane-parallel
construction, ordinarily designated as the applanation plate) is fitted at the
narrower end of a conically widening carrier sleeve 28. The connection between
the contact element 24 and the carrier sleeve 28 may be inseparable, for
example by virtue of adhesion, or it may be separable, for instance by virtue
of a
screwed joint. At its wider sleeve end the carrier sleeve 28 has, in a manner
not
represented in any detail, suitable coupling structures for coupling onto the
focusing objective 18.
The laser source 12 and the scanner 16 are controlled by a control computer 30
which operates in accordance with a control program 34 stored in a memory 32.
The control program 34 contains instructions (program code) that upon
execution by the control computer 30 bring about such a local control of the
beam focus of the laser beam 14 that a LASIK flap arises in the cornea of the
eye 22 bearing against the contact element 24. The incision figure generated
in
the cornea in this regard encompasses not only a flap incision forming the
actual
flap but additionally an auxiliary incision, through which photodisruption
gases
arising are able to escape from the cornea to the outside.
Figures 2a and 2b show two variants of such an incision figure. In both cases
a
dashed circular line 36 denotes the levelling region in which the cornea is
levelled as a consequence of its abutment against the contact element 24. It
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will be understood that, in reality, the levelling region 36 does not have to
be
exactly circular. In particular, in view of the ordinarily differing radii of
curvature
in the principal meridional directions of the surface of the cornea an outline
of
the levelling region 36 deviating from a circular shape may arise.
In the exemplary cases that are shown, the flap incision forming the flap is
composed of two partial incisions. A first partial incision is a so-called bed
incision, which severs the flap from the stromal bed and is realised as a flat
surface incision parallel to the contact face 26. The bed incision is denoted
by
io 38 in Figures 2a and 2b. Said bed incision is produced at a depth of the
cornea
corresponding to the desired thickness of the flap. Whereas in Figure 2b it
extends over a complete circular area, in Figure 2a it is shortened by a
segment
of a circle and terminates at a chord of a circle. It will be understood that,
depending on the desired shape of the flap, the bed incision 38 may have a non-
is circular outline, for example an elliptical outline. In any case, the
bed incision 38
is complemented by a lateral incision 40 which proceeds along a partial
periphery of the bed incision 38 and - considered locally ¨ extends to the
surface
of the cornea, beginning from the bed incision 38. The lateral incision 38 is
also
generated in the levelled state of the cornea, i.e. with the eye 22 bearing
against
zo the contact face 26, and proceeds obliquely outwards locally from the
bed
incision 38. Alternatively, the lateral incision 40 may proceed obliquely
inwards
locally from the bed incision 38.
The flap is formed by the bed incision 38 and the lateral incision 40
together.
25 Said flap is denoted by 42 in Figures 2a and 2b and also in Figure 3. In
the part
of the periphery of the bed incision 38 not encompassed by the lateral
incision
40 the flap 42 is still connected to the remaining corneal tissue (apart from
the
region of an auxiliary incision yet to be elucidated). The transition region
between the flap 42 and the remaining corneal tissue forms a hinge which
30 permits the flap to be folded away in order to expose the underling
tissue for an
ablating laser treatment. The hinge line is, at least in sufficient
approximation,
rectilinear and is denoted by 44 in Figs. 2a and 2b. In the case of Fig. 2a,
it is
situated approximately overlapping the straight edge of a segment of a circle
at
which the bed incision 38 terminates; in Fig. 2b it proceeds, at least when
35 considered in the top view of this Figure ¨ transversely beyond the bed
incision
38 from one peripheral end of the lateral incision 40 to the other.
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Figure 3 illustrates the two partial incisions (bed incision, lateral
incision) of the
flap 42 for the case of Figure 2a with the cornea relaxed, i.e. after removal
of
the eye 22 from the contact element 24. The curved line 48 which has been
drawn with dashes designates the anterior surface of the cornea.
As a consequence of the vaporisation of corneal tissue in the course of the
cutting of the flap 42, gases arise which are able to diffuse out of the cut
surface
into the adjoining tissue regions. The residence of such gases in the eye may,
on the one hand, be dangerous if the gases penetrate into particularly
sensitive
regions of the eye; on the other hand, it may impair the functionality of an
eye-
tracker in the course of the subsequent laser ablation of the stromal bed.
Therefore the incision figure generated in the cornea is not only limited to
the
flap incision but exhibits an additional auxiliary incision 50 which enables
an
escape from the eye of the gases arising in the course of preparation of the
flap.
In the exemplary cases of Figures 2a, 2b which are shown, the auxiliary
incision
50 directly adjoins the bed incision 38, to be specific in the hinge region of
the
flap 42 - that is to say, where the lateral incision 40 leaves free a part of
the
periphery of the bed incision 38. Starting from the bed incision 38, the
auxiliary
incision 50 extends locally away from the flap 42 in the direction towards the
corneal surface 48, i.e. it proceeds on the other side of the flap 42. In this
case
the auxiliary incision 50 proceeds locally at increasingly smaller depth
within the
cornea; in particular, it ascends steadily to higher corneal layers until it
reaches
the surface of the cornea. In this way it forms a channel (tunnel), by which
the
bed incision 38 is connected with the environment outside the eye, so that
gases
that arise in the course of the cutting of the bed incision 38 are able to
escape
outwards through the channel.
As can be discerned in Figures 2a, 2b, in the exemplary cases that are shown
the channel formed by the auxiliary incision 50 has a constant width over its
length, being narrower than the hinge region of the flap 42 and, relative to
the
direction of the hinge axis 44, situated approximately centrally in the hinge
region. It will be understood that the auxiliary incision 50 may also be as
wide
as the hinge region or even wider than the latter. Restrictions in this regard
are
not intended within the scope of the invention.
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In Figure 3 the auxiliary incision 50 is represented as a rectilinear
incision. It will
be understood that the auxiliary incision 50 may alternatively rise in a
curved
path locally from the bed incision 38 to the surface of the cornea. The
intensity
of the ascent of the auxiliary incision 50 may also be defined differently.
Comparable remarks apply to the width of the auxiliary incision 50; said width
may vary over the length of the auxiliary channel; for example, it may become
larger in the direction towards the surface of the cornea.
The point at which the auxiliary incision 50 reaches the surface of the cornea
may lie outside the levelling region 36 of the cornea, as indicated in Figures
2a,
2b where the auxiliary incision 50 extends outwards beyond the levelling
region
36. Nevertheless, it is just as possible that the auxiliary incision 50 is
guided
locally up to the surface of the cornea within the levelling region 36 or at
the
edge of the levelling region.
For the purpose of elucidating the temporal sequence in which the auxiliary
incision 50 and the bed incision 38 are inserted, and the scan patterns that
are
used in the process for the laser beam 14, reference will now additionally be
made to Figure 4. The bed incision 38 and the auxiliary incision 50 are shown
therein; the lateral incision 40 has been omitted for the sake of clarity of
layout;
it is usually generated only after the bed incision 38, to be specific
starting from
the bed incision 38 in the direction towards the surface of the cornea.
The auxiliary incision 50, on the other hand, is generated before the bed
incision
38 is inserted. This guarantees that gases are able to escape outwards via the
auxiliary incision 50 already at the start of the preparation of the bed
incision 38.
The auxiliary incision 50 is generated from the surface of the cornea - that
is to
say, in the direction towards deeper corneal layers. This is indicated by an
arrow 52 which has been drawn at the top in Figure 4. After generation of the
auxiliary incision 50, the bed incision 38 is generated, to be specific
beginning in
the hinge region 44 - that is to say, where the auxiliary incision 50
terminates.
Beginning from the hinge region 44, the bed incision 38 is gradually generated
in the direction towards the end that is remote from the hinge. This direction
of
generation of the bed incision 38 is indicated at the top in Figure 4 by an
arrow
54.
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On its largest part the auxiliary incision 50 is generated by line scans of
the laser
beam 14 that follow one another, line by line, in the arrow direction 52, i.e.
in
the direction from the surface of the cornea towards the bed incision 38. The
individual scan lines of this line scan are denoted by 56. The bed incision 38
is
also generated with a scan pattern consisting of line scans, the individual
scan
lines following one another in the direction from the hinge region 44 towards
the
end of the bed incision 38 that is remote from the hinge, i.e. in the arrow
direction 54. The scan lines of the bed incision 38 are denoted by 58 in
Figure 4.
Whereas the representation shown in Figure 4 is an example of a succession of
the scan lines 56 in the direction of the longitudinal extent of the auxiliary
incision 50 Clongitudinal extent' in this connection means an extent from the
surface of the cornea to the flap incision, more precisely to the bed
incision), it is
readily conceivable to generate the main part of the auxiliary incision 50
with a
line scan, the scan lines of which follow one another at right angles to the
longitudinal extent of the auxiliary incision. The scan lines of such a
transverse
scan then proceed similarly to the scan lines 60 and 64.
The transition region between the auxiliary incision 50 and the bed incision
38 is,
in addition, prepared with line scans that progress, line by line, at right
angles to
the transition direction. 'Transition direction' here means the direction in
which
the auxiliary incision 50 merges with the bed incision 38. This direction
corresponds to the direction of the arrows 52, 54. By producing scan lines
alongside one another at right angles to this direction in the transition
region, it
is possible to realise a good connection, open for the passage of gas, between
the auxiliary incision 50 and the bed incision 38. The transverse scan lines
that
have been produced in the transition region are denoted by 60 in Figure 4. The
direction of their succession is represented by an arrow 62 (may optionally
also
be in the opposite arrow direction).
Similar transverse scan lines are, furthermore, produced in the entry region
of
the auxiliary incision 50 - that is to say, where it enters the corneal tissue
on the
surface of the cornea. The corresponding scan lines are denoted by 64 in
Figure 4; the direction of their succession is indicated by an arrow 66 (may
optionally also be in the opposite arrow direction). These scan lines 64
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proceeding at right angles to the entry direction of the auxiliary incision
are
expedient in order to create a clean opening of the auxiliary incision 50 on
the
surface of the cornea.
As far as the temporal sequence is concerned, expediently firstly the scan
lines
64 are produced, subsequently the scan lines 56, thereupon the scan lines 60
and, thereafter, the scan lines 58. In this manner the generation of the
incisions
progresses increasingly from the surface in the direction towards deeper
layers.
The representation in the lower part of Figure 4 illustrates this once again.
Therein the auxiliary incision 50, the bed incision 38 and also the entry
region
(denoted by 68) and the transition region between the two incisions (denoted
by
70) are shown in a view from the side. With the temporal sequence of the scan
lines that has been elucidated it is possible that during the generation of
the
auxiliary incision 50 and also during the generation of the bed incision 38 a
tunnel to the outside is already always open, through which gases currently
arising are able to escape.
In a modification of the above sequence, the generation of the transition
region
70 may be temporally favoured and may be undertaken ahead of the entry
region 68. After this, as previously, the remainder (i.e. the main part) of
the
auxiliary incision 50 and also the bed incision 38 are inserted. In a further
modification, firstly the transition region 70 may be generated. Then the main
part of the auxiliary incision 50 and, after this, the entry region 68 are
generated. After complete generation of the auxiliary incision 50, the bed
incision 38 is inserted. Though it should be pointed out that within the scope
of
the invention no restriction whatsoever to a defined temporal sequence of the
generation of the incisions is intended.
In principle, in the entire auxiliary incision 50 (including the entry region
68 and
the transition region 70) and also in the bed incision 38 the local spacings
of the
photodisruptions following one another along the scan lines may be
substantially
the same. The same applies to the mutual spacing of consecutive scan lines.
However, it is possible to vary the local spacing of the photodisruptions
or/and
the mutual line spacing at least in parts of the auxiliary incision 50 or/and
of the
bed incision 38. In particular, it is conceivable to choose for the entry
region 68
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or/and for the transition region 70 a closer local succession of the
photodisruptions or/and to choose a closer mutual spacing of the consecutive
scan lines than for the main part of the auxiliary incision 50 and for the bed
incision 38.
The position of the auxiliary incision 50 described here relative to the bed
incision 38 guarantees that the two incisions do not overlap reciprocally.
This is
because no further underlying plane can be cut through an already cut plane.
Since in the ideal case the auxiliary incision 50 should already be present
when
the cutting of the bed incision 38 is begun, it is advisable to cut the
auxiliary
incision 50 into the cornea from outside the flap (further remote from the
corneal centre) and to allow it to merge with the bed incision in the hinge
region
of the flap.
In Figures 5 and 6, identical or identically-acting elements are denoted by
the
same reference symbols as in the preceding Figures, but supplemented by a
lower-case letter. To the extent that nothing else results in the following,
reference is made to what was stated above for the purpose of elucidating
these
elements.
It has already been explained that the auxiliary incision may open out to the
surface of the eye inside or outside the levelled region of the cornea. This
assertion may be generalised to the extent that the auxiliary incision may
open
out to the surface of the cornea at a point that lies inside or outside (or at
the
edge of) a region in which the cornea bears against the contact element of the
patient adapter. Even though within the scope of the invention a very
extensive
levelling of the surface of the cornea by the contact element is striven for,
it is
nevertheless not necessary that the cornea bears against the contact face
exclusively in flat regions of said contact face.
In this regard, reference will now be made to the variant shown in Figure 5.
Therein a contact element 24a is shown which on its underside facing towards
the eye bears a contact face 26a which in its main part is of flat
construction but
in its marginal region is rounded and proceeds there obliquely to the flat
main
part in the direction away from the eye 22a. The rounded surface portion forms
a ring segment surrounding the flat main part of the contact face 26 and is
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denoted by 72a. The flat main part of the contact face 26a, on the other hand,
is denoted by 74a. The contact between the contact element 24a and the eye
22a is established in such a way that the cornea rests closely against the
contact
face 26a not only in the main part 74a but also in the outer ring segment 72a.
The auxiliary incision 50a is generated in such a way that it emerges to the
surface of the cornea in the region of the ring segment 72a (the term 'emerge'
is
meant here purely locally and implies no statement whatsoever about the
temporal sequence in which the individual parts of the auxiliary incision are
prepared). This means the auxiliary incision 50a opens out at a point on the
surface of the cornea where the cornea bears against the rounded ring segment
72a. This is favourable to the extent that any possible gases which arise in
the
course of preparation of the auxiliary incision 50a and of the bed incision
38a
and escape to the outside though the auxiliary incision 50a can, at least for
the
most part, reach the surrounding air and are not drawn deeper between the
contact element 24a and the corneal surface 48a by capillary action. In other
words, a better degassing of the operative field is possible in this way.
The rounded ring segment 72a adjoins the flat main part 74a of the contact
face
26a preferentially in kink-free manner. Nevertheless, it is not to be excluded
in
principle to construct the ring segment 72a, instead of with a roundish
configuration, in the form of a rectilinear oblique surface which is separated
from
the flat main part 74a by a kink.
The variant shown in Figure 6 illustrates an example in which the auxiliary
incision 50b opens out at a point on the surface of the cornea where the
cornea
does not bear against the contact face 26b of the contact element 24b.
Instead,
it opens out outside the flattened region of the corneal surface 48b. In
concrete
terms, in the exemplary case shown in Figure 6 the auxiliary incision 50 opens
out into an annular chamber 76b which is delimited between the contact
element 24b, the corneal surface 48b and a sealing component 78b which, for
example, may be part of a suction ring (not represented in any detail) to be
attached onto the eye 22b. Represented schematically in Figure 6 is a filling
channel 80b, via which the annular chamber 76b is capable of being filled with
a
physiological liquid (e.g. solution of common salt). The filling channel 80b
may
be part of the aforementioned suction ring.
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The bed incision 38b and the auxiliary incision 50b may in this variant be
generated in a common plane, i.e. with constant z-position of the beam focus
of
the laser radiation that is used for the generation of the incisions. The
direction
of generation corresponds to that shown in Figure 4, i.e. the auxiliary
incision
50b is generated before the bed incision 38b, to be specific expediently in a
direction from the surface of the cornea to the bed incision 38b.
