U.S. patent application number 12/227533 was filed with the patent office on 2009-09-24 for corneal implant and method for correction of impaired vision in the human eye.
Invention is credited to Albert Daxer.
Application Number | 20090240327 12/227533 |
Document ID | / |
Family ID | 38446345 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090240327 |
Kind Code |
A1 |
Daxer; Albert |
September 24, 2009 |
Corneal Implant and Method for Correction of Impaired Vision in the
Human Eye
Abstract
Corneal implant to be introduced into the optical centre (Z) of
the cornea of the human eye for the purpose of correcting impaired
vision, in particular presbyopia, or presbyopia in combination with
hypermetropia or myopia. To propose a corneal implant which is
suited for introduction into the optical centre (Z) of the human
eye, and which may be applied for correcting presbyopia on its own
or in combination with hypermetropia or myopia, the effective
thickness (d) of the corneal implant (2), measured in the direction
of the optical axis (5) of the eye, must be larger than 50 .mu.m
and the maximum width (b), measured in a plane perpendicular to the
direction of thickness, must be less than 1 mm, the corneal implant
(2) having no imaging function in relation to the human eye.
Inventors: |
Daxer; Albert; (Linz,
AT) |
Correspondence
Address: |
COLLARD & ROE, P.C.
1077 NORTHERN BOULEVARD
ROSLYN
NY
11576
US
|
Family ID: |
38446345 |
Appl. No.: |
12/227533 |
Filed: |
May 23, 2007 |
PCT Filed: |
May 23, 2007 |
PCT NO: |
PCT/EP2007/055015 |
371 Date: |
November 20, 2008 |
Current U.S.
Class: |
623/5.11 |
Current CPC
Class: |
A61F 2/14 20130101; A61F
2/142 20130101; A61F 2/1451 20150401; A61F 2/147 20130101 |
Class at
Publication: |
623/5.11 |
International
Class: |
A61F 2/14 20060101
A61F002/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2006 |
AT |
A 885/206 |
Claims
1. Corneal implant to be introduced into the optical centre (Z) of
the cornea of the human eye for the purpose of correcting impaired
vision, in particular presbyopia, or presbyopia in combination with
hypermetropia or myopia, wherein the effective thickness (d) of the
corneal implant (2), measured in the direction of the optical axis
(5) of the eye, is more than 50 .mu.m (micron) and the maximum
width (b), measured in a plane perpendicular to the direction of
thickness, is less than 1 mm, with the corneal implant (2) having
no imaging function in relation to the human eye.
2. Corneal implant according to claim 1, wherein the ratio between
maximum width (b) and effective thickness (d) is less than three
and/or higher than one.
3. Corneal implant according to claim 1, wherein the effective
thickness (d) of the corneal implant (2), measured in the direction
of the optical axis (5) of the eye, is less than 500 .mu.m.
4. Corneal implant according to claim 1, wherein the smallest width
of the corneal implant is not more than 30 percent smaller than the
largest width (b).
5. Corneal implant according to claim 1, wherein it is
rotation-symmetrically arranged around the axis along the effective
thickness (d).
6. Corneal implant according to claim 1, wherein it has the shape
of a sphere.
7. Corneal implant according to claim 1, wherein it is opaque or
semi-transparent.
8. Corneal implant according to claim 1, wherein it is black.
9. Method for the correction of refractive errors in the human eye,
in particular for the correction of presbyopia on its own or in
combination with hypermetropia, by introducing a corneal implant
(2) into the optical centre (Z) of the cornea (1) of the human eye,
including the following step: Introducing a corneal implant (2)
without an imaging function in relation to the human eye, with an
effective thickness (d) of more than 50 .mu.m, measured in the
direction of the optical axis (5) of the eye, and a maximum width
(b) of less than 1 mm, measured in a plane perpendicular to the
direction of thickness, into the optical centre (Z) of the cornea
(1) so as to deflect the surface of the cornea (1) in its optical
centre (Z).
10. Method for the correction of refractive errors in the human
eye, in particular for the correction of presbyopia on its own or
in combination with hypermetropia, by introducing a corneal implant
(2) into the optical centre (Z) of the cornea (1) of the human eye,
including the following step: Introducing several corneal implants
(2) without an imaging function in relation to the human eye, each
having an effective thickness (d) of more than 50 .mu.m, measured
in the direction of the optical axis (5) of the eye, and a maximum
width (d) of less than 1 mm, measured in a plane perpendicular to
the direction of thickness, into the optical centre (Z) of the
cornea (1) so as to deflect the surface of the cornea (1) in its
optical centre (Z).
11. Method according to claim 9, wherein the ratio between the
width (b) and the effective thickness (d) is less than three and/or
higher than one.
12. Method according to claim 9, wherein the corneal implant (2)
has the shape of a sphere.
13. Method according to claim 9, wherein das corneal implant (2) is
opaque or semi-transparent.
14. Corneal implant according to claim 9, wherein it is black.
15. Method for the correction of refractive errors in the human
eye, in particular for the correction of presbyopia and myopia, by
introducing a corneal implant (2) into the optical centre (Z) of
the cornea (1) of the human eye, including the following steps:
Introducing one or several corneal implants (2) without an imaging
function in relation to the human eye, with an effective thickness
(d) of more than 50 .mu.m, measured in the direction of the optical
axis (5) of the eye, and a maximum width (d) of less than 1 mm,
measured in a plane perpendicular to the direction of thickness,
into the optical centre (Z) of the cornea (1) so as to deflect the
surface of the cornea (1) in its optical centre (Z). Introducing a
ring-shaped corneal implant (10) outside of the optical centre (Z)
of the cornea (1), assuring that the curvature (R) of the cornea
(1) outside of the optical centre (Z) is changed.
16. Method according to claim 15, wherein the ratio between the
width (b) and the effective thickness (d) of the corneal implant
(2) introduced into the optical centre (Z) of the cornea (1) is
less than three and/or higher than one.
17. Method according to claim 15, wherein the corneal implant (2)
introduced into the optical centre (Z) of the cornea (1) has the
shape of a sphere.
18. Method according to claim 15, wherein the corneal implant (2)
introduced into the optical centre (Z) of the cornea (1) is opaque
or semi-transparent.
19. Corneal implant according to claim 15, wherein it is black.
20. Method for the correction of refractive errors in the human
eye, in particular for the correction of presbyopia or myopia, by
introducing a corneal implant (2) into the optical centre (Z) of
the cornea (1) of the human eye, including the following steps:
Introducing one or several corneal implants (2) without an imaging
function in relation to the human eye, with an effective thickness
(d) of more than 50 .mu.m, measured in the direction of the optical
axis (5) of the eye, and a maximum width (d) of less than 1 mm,
measured in a plane perpendicular to the direction of thickness,
into the optical centre (Z) of the cornea (1) so as to deflect the
surface of the cornea (1) in its optical centre (Z). Introducing
several corneal implants (11) that change the curvature (R) of the
cornea (1) outside the optical centre (Z) of the cornea (1).
21. Method according to claim 20, wherein the ratio between the
width (b) and the effective thickness (d) of the corneal implant
(2) introduced into the optical centre (Z) of the cornea (1) is
less than three and/or higher than one.
22. Method according to claim 20, wherein the corneal implant (2)
introduced into the optical centre (Z) of the cornea (1) has the
shape of a sphere.
23. Method according to claim 20, wherein the corneal implant (2)
introduced into the optical centre (Z) of the cornea (1) is opaque
or semi-transparent.
24. Corneal implant according to claim 20, wherein it is black.
Description
AREA OF THE INVENTION
[0001] The present invention relates to a corneal implant to be
inserted into the optical centre of the cornea of the human eye for
the purpose of correcting impaired vision, in particular presbyopia
in otherwise emmetropic eyes (eyes with normal vision) as well as
presbyopia in combination with hypermetropia (farsightedness) or
myopia (nearsightedness).
[0002] The present invention furthermore relates to a procedure for
correcting impaired vision in the human eye, in particular for
correcting presbyopia, presbyopia in combination with
hypermetropia, presbyopia in combination with myopia, and
presbyopia in combination with astigmatism, by inserting a corneal
implant into the optical centre of the cornea.
[0003] The optical apparatus of the human eye that generates an
optical image of the environment basically comprises the cornea and
the lens, which is positioned behind the iris. This optical
apparatus of the eye has a total refractive power of approximately
60 dioptres, with the interface between the cornea and the
air--i.e. the outer boundary of the eye--with approximately 40
dioptres accounting for most of the refractive power. This
refractive power of the cornea is in general indirectly
proportionate to the radius of the corneal surface (interface
between cornea and air). A change in the radius of the curvature of
the cornea also leads to a change in the refractive power of the
eye.
[0004] In the case of myopia or nearsightedness, the eyeball is too
long and the refractive power of the cornea thus inadequate to
assure that the light rays are focussed on the retina; these are
focussed in front of the retina instead.
[0005] In the case of hypermetropia or farsightedness, the eyeball
is too short and the refractive power of the cornea thus
insufficient to assure that the light rays are correctly focussed
on the retina; they are focussed behind the retina instead.
[0006] Presbyopia is a dissociation of the refractive power of the
eye in that for accurate far vision a different correction of
dioptres than for accurate near vision is required.
[0007] Different options for correcting these refractive errors are
available. In addition to the classical methods of vision
correction via glasses or contact lenses, also surgical methods are
known where implants are inserted into the cornea of the human eye
with the aim to either modify the curvature of the cornea and thus
correct the refractive power of the latter accordingly, or to alter
the optical properties of the cornea through the optical properties
of the implant.
[0008] By enlarging the radius of curvature of the cornea the
refractive power is reduced, which allows to correct a myopic
condition. To be able to correct a hyperopic condition, the corneal
radius needs to be reduced, i.e. the curvature needs to be
increased.
[0009] To be able to correct presbyopia by surgical intervention,
it is necessary to impart a certain degree of bi-focality or
multi-focality to the refractive power of the cornea. This means
that the refractive power of the cornea is designed in a way that
the light rays entering the eye from different distances (near or
far away), depending on their point of entry, are simultaneously
focussed on the retina, or more precisely in the central area of
the retina (=the macula, the area where accurate vision occurs).
This implies that one or several images from a far distance and one
or several images from a near distance are simultaneously focussed
in the macula. The brain then selects the appropriate image. To
allow this selection to take place, the far-away image and the near
image must have about the same intensity. The use of contact lenses
and intraocular lenses, which are inserted after cataract surgery,
are based on this principle.
STATE OF THE ART
[0010] WO 93/05731 reports the insertion of an optical lens into
the optical centre of the cornea, the dimensions of which are
smaller than those of the optical zone being limited by the
diameter of the pupil.
[0011] The optical centre of the cornea is that part of the cornea
along which the optical axis of the eye passes through the cornea.
The optical axis is the axis of projection of the optical system of
the eye. The ophthalmologist determines the optical centre by using
specific assessment methods. The ophthalmologist may choose from a
wide variety of different methods. The methods for determining the
optical centre of the cornea described hereinafter represent only a
small portion of the many different methods commonly applied, and
are not exhaustive. Many systems, in particular excimer laser
systems with active eye tracking, use the centre of the pupil or
its projection on the corneal surface or around a point at an
individually defined distance as the optical centre of the cornea.
Other common systems are aimed at the area where the curvature of
the cornea is most pronounced. Especially in the case of
high-degree myopia, in fact, an angular deflection of the optical
axis from the anatomical axis is to be noticed, which is defined as
the "kappa angle". Another method relates to the so-called
"Purkinje reflexes". These are reflexes on the corneal front and
back faces as well as on the lens front and back faces, which occur
when the patient focuses on a preferrably point-shaped light
source. While these reflexes ideally overlap, most of the time this
is not the case; the eye specialist then chooses one of these
reflexes as the optical centre. It is also quite common to choose
the middle position of all four reflexes, or the middle between
this middle position and the centre of the pupil etc. Eventually,
it is left to the personal discretion, individual experience and
preference of the eye specialist how he determines the optical
centre of the cornea. Generally speaking, the various methods used
for determining the optical centre of the cornea tend to render
quite similar results.
[0012] In WO 93/05731, the implantation of an optical lens in the
optical centre of the cornea results in various zones of different
refractive power, namely in the area of the optical lens itself as
well as in the adjoining corneal tissue through the refractive
power of the cornea proper. This allows to create a certain degree
of bifocality or multifocality, depending on the contour of the
optical surface of the implanted lens. The thickness of the lenses
in the direction of the optical axis of the eye is less than 50
.mu.m to avoid an undesirable deflection of the cornea and an
impairment of the refractive power of the lens. Basically, however,
there is the disadvantage that the newly created boundary surfaces
may produce optically adverse phenomena such as glares and
reflections, which the patient will find disturbing. The optical
surface therefore needs to be excellently designed, which in case
of such small dimensions is a rather difficult and tedious
undertaking. It is also known that organic deposits tend to form
along the boundaries of corneal implants, which may substantially
impair the function of the implants as optical elements.
[0013] U.S. Pat. No. 6,589,280 B1 describes a method of creating a
multi-focal cornea by implanting a minimum of 50 microscopically
small optical lenses outside the optical centre of the cornea. Each
lens should have a defined refractive power, preferrably 1 to 3
dioptres. The optical lenses have a thickness of approx. 2-3 .mu.m
and a width of less than 1 mm (measured in a plane perpendicular to
the direction of thickness). The lenses are so small that the
curvature of the cornea is not impaired by the deflection of the
corneal surface. The refractive error is corrected exclusively
through the different refractive power of the individual lenses.
The described method is extremely complicated and, with regard to
its usability in living tissue, the same arguments as mentioned
earlier apply.
[0014] U.S. Pat. No. 5,722,971 describes a method where a thin
plate-shaped implant with diffractive optics and a hole at its
centre is implanted. The outer diameter is in a range between 3 mm
and 9 mm. In addition, ring implants as well as ring replacement
implants are presented. In this case, the ring is replaced by
several individual implants which are concentrically positioned
along a circle around the centre of the cornea. By leaving
individual positions of the circle empty, not only myopic
conditions but also regular and irregular astigmatisms may be
corrected. No reference is made to the dimensions of the
replacement implants, but the illustrations provided reveal that in
order for the replacement implants to have the same effect as the
rings, they must replace about the same volume and therefore, as is
also shown in the drawings, must have a much bigger size and
dimensions that correspond to the pupil width or iris width.
Moreover, there is no detailed information as to their geometry.
The illustrated applications imply that they must have the shape of
a protracted ellipsoid. Such implants are not suited for use in the
area of the central cornea.
[0015] The same applies with respect to US 2004/0073303 A1, where
the preferred embodiment of the invention is even a curved,
protracted implant (centroid).
[0016] A state-of-the-art method therefore is to implant optical
lenses as corneal implants in the optical centre of the cornea.
These optical corneal implants exert their effect via their own
refractive power. They have an optically effective front and/or
back face and also contain a material with a specific refractive
index, which is positioned between the optically effective front
and/or back face and defines both the contour and the refractive
power of these optical corneal implants. It is also known, however,
that in such optical corneal implants there is the tendency that in
the area of contact with the surrounding tissue purely optical
phenomena occur and organic material is deposited. Especially in
implants which are inserted into the optical centre of the human
eye, this leads to a significant impairment of vision.
[0017] Although implants positioned outside of the optical centre
are less sensitive to the aforementioned deposits, they are not
able to create bi-focality let alone multi-focality to correct
presbyopia on its own or in combination with hypermetropia or
myopia.
DESCRIPTION OF THE INVENTION
[0018] The aim of the present invention therefore is to suggest a
corneal implant which is suited for introduction into the optical
centre of the human eye and which may be used to correct presbyopia
on its own as well as presbyopia in combination with hypermetropia
(farsightedness) or myopia (nearsightedness).
[0019] According to the invention, this is achieved through the
characteristics of claim 1. The aim is to provide the corneal
implant with an effective thickness, measured in the direction of
the optical axis of the eye, of more than 50 .mu.m and a maximum
width, measured in a plane perpendicular to the direction of
thickness, of less than 1 mm, the corneal implant having no imaging
function in relation to the human eye.
[0020] A corneal implant of the selected dimensions is on one hand
suited for being positioned in the optical centre of the human eye
without impairing the vision of the human eye, and on the other
also suited for correcting presbyopic vision by modifying the
curvature of the cornea through corneal deflection in its optical
centre. Since a corneal implant according to the invention has no
imaging function in relation to the human eye, which means that it
has no optical effect whatsoever, it is relatively easy to produce.
The dimensions according to the invention allow to introduce the
implant directly into the optical centre of the eye without
reducing its vision. Resulting from the central addition of volume
an aspherical surface contour of the cornea may be produced in the
surroundings of the corneal implant, which facilitates a
multi-focal image so as to correct presbyopic vision. Corrections
of hyperopic conditions are possible as well. The implantation in
the optical centre of the cornea implies that the implant, with due
consideration of the finite defining accuracy of the optical centre
and the finite positioning accuracy of the implant in the cornea,
is introduced into the cornea along a line that represents the
optical centre, i.e. the line along which the optical axis passes
through the cornea.
[0021] Contrary to the state of the art, the implant deliberately
fails to support optical imaging. The optical effect of the implant
is thus indirectly achieved and determined by the contour of the
transitional area in the adjoining tissue. Since the implant
according to the invention has no direct optical imaging function,
it needs no optically designed surfaces. The implant surfaces may
be flexibly shaped and are not bound by optical requirements such
as in optically effective implants. The geometry of the implant is
exclusively determined by geometrical considerations regarding the
type of replacement of the tissue surrounding the implant. What was
said also implies that an implant according to the invention which
corresponds to a preferred embodiment of the invention need not be
transparent, but may also be opaque or partly transparent and of
any sort of colour in order to assume its function according to the
invention. Since under certain conditions (geometry) disturbing
surface phenomena may occur at the transparent faces (similar to
optical implants), while the geometry may display a favourable
tissue replacement behaviour, this side effect may be eliminated by
eliminating or reducing the transparency of the corneal implant. In
case a colour is to be added to the corneal implant, black has
proven to be particularly advantageous as it does not stand out
from the underlying black colour of the pupil.
[0022] In any case, in an implant according to the invention, even
if it were made of transparent material, the proportion of light
rays entering the implant after its introduction into the cornea in
no way contributes to the perception of a retinal image, which
means it fails to project a perceivable image on the retina. Among
other things, this stems from the dimensions and measurements of
the implants according to the invention, their geometry, their
surface properties, their material, their colour, optical losses
occurring along the area of contact with the surrounding tissue as
well as biological interaction with the surrounding tissue. This is
particularly the case if the implant has been embedded in the
tissue for a certain period of time. This, in particular, makes the
effect of the implant insensitive to optical and biological surface
phenomena, by which it differs from state-of-the-art products.
[0023] Since the eye complies with the laws of geometrical optics,
and the latter basically corresponds to the optics of the rays
close to the axis, an expert would expect that by introducing a
non-optical body--typically representing an optical obstacle--into
the optical centre of the cornea, the vision would be substantially
impaired. Surprisingly, it could be shown that if this body has the
characteristics according to the invention, such impairment will
only be minimal.
[0024] In a preferred embodiment of the invention, the ratio
between width and effective thickness of an implant according to
the invention is less than three and/or more than one. It has been
shown that in this case particularly positive results regarding
multi-focality can be achieved.
[0025] Effective thicknesses of less than 500 .mu.m and width
variations not exceeding 30 percent of the largest width also help
to adjust the outline of the corneal surface to the requirements of
multi-focal imaging.
[0026] In another preferred embodiment of the invention, the
corneal implant is rotation-symmetrically arranged around the axis
along the effective thickness. In a particularly preferred
embodiment, the corneal implants have the shape of a sphere, thus
assuring an ideal formation of the aspherical surface contour on
the corneal surface.
[0027] It is yet a further task of the present invention to suggest
a method for the correction of impaired vision in the human eye, in
particular for the correction of presbyopia on its own or in
combination with hypermetropia, by inserting a corneal implant into
the optical centre of the human eye without risking that the
function of the implant is impaired by deposits in the optical
centre of the cornea around the implant and without the need to use
sophisticated optical lenses as implants.
[0028] According to the invention, this task is achieved through
the characteristics of claim 9 or 10.
[0029] The aim is to introduce into the optical centre of the
cornea of the human eye one or several corneal implants without an
imaging function in relation to the human eye, each of which has an
effective thickness of more than 50 .mu.m, measured in the
direction of the optical axis of the eye, and a maximum width of
less than 1 mm, measured in a plane perpendicular to the direction
of thickness, with the purpose of modifying the curvature of the
corneal surface around the optical centre of the cornea through
deflection of the corneal surface in the optical centre.
[0030] Another task of the present invention is to suggest a method
for the correction of impaired vision in the human eye, in
particular for the correction of presbyopia in combination with
myopia, by introducing a corneal implant into the optical centre of
the human eye without risking that the function of the implant is
impaired by deposits in the optical centre of the cornea around the
implant and without the need to use sophisticated optical lenses as
implants.
[0031] According to the invention, this task is achieved through
the characteristics of claim 15 or 20. The aim is to introduce into
the optical centre of the cornea one or several corneal implants
without an imaging function in relation to the human eye, which
have an effective thickness of more than 50 .mu.m, measured in the
direction of the optical axis of the eye, and a maximum width of
less than 1 mm, measured in a plane perpendicular to the direction
of thickness, for the purpose of accomplishing a deflection of the
surface of the cornea in its optical centre; several corneal
implants, preferrably one ring-shaped corneal implant, are
additionally positioned outside the optical centre of the cornea,
assuring that the curvature of the cornea outside the optical
centre is modified.
[0032] The following is a detailed description of the invention
using examples of embodiments, from which the expert may deduce
additional advantages of the invention. The figures show the
following:
SHORT DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 cross section of the cornea of a human eye with an
implanted corneal implant in keeping with the invention
[0034] FIG. 2 cross section of the cornea of a human eye with an
implanted corneal implant in keeping with the invention, where the
different effective areas are marked
[0035] FIG. 3 cross section of a corneal implant in keeping with
the invention
[0036] FIG. 4 cross section of an alternative corneal implant in
keeping with the invention
[0037] FIG. 5a-s further alternative cross sections of corneal
implants according to the invention
[0038] FIG. 6a-b corneal implant according to the invention in
combination with a ring-shaped corneal implant
[0039] FIG. 7a-b corneal implant according to the invention in
combination with several individual corneal implants
[0040] FIG. 8a-b corneal implant according to the invention in
combination with several individual aligned corneal implants
WAYS TO EXECUTE THE INVENTION
[0041] FIG. 1 shows a cross section of the cornea 1 of a human eye
with a radius of curvature R including an optical centre Z. A
corneal implant 2 according to the invention is implanted in the
corneal tissue of the cornea 1, having an effective thickness d of
more than 50 .mu.m, measured in the direction of the optical axis 5
of the eye, and a width b of less than 1 mm, measured in a plane
perpendicular to the direction of thickness.
[0042] The corneal implant 2 has no imaging function in relation to
the human eye, which means that the light rays entering the eye are
not focussed on the retina (not depicted in the drawings) of the
eye due to the optical properties of the corneal implant 2
according to the invention. Instead, the implantation of the
corneal implant 2 results in a central volume addition and thus in
an aspherical surface contour 3 of the cornea 1 around the optical
centre Z of the cornea, which also facilitates multi-focal
imaging.
[0043] In contrast to the known state-of-the-art corneal implants
and vision correction methods, the aim of the present invention is
to introduce a corneal implant 2 into the optical centre Z of the
eye which deliberately lacks an optical function and which serves
to correct the impaired vision exclusively by altering the
curvature R of the cornea 1 around the corneal implant.
[0044] While this also leads to deformations in the area of the
corneal back face 4, these are of only minor relevance for vision
correction.
[0045] In keeping with the invention, the corneal implant 2 may be
of any type of transparency: it may be fully opaque,
semi-transparent, or fully transparent. Based on the fact that the
corneal implant 2 has no imaging function in relation to the eye,
it may be of any colour whatsoever, preferrably black to assure
compatibility with the black pupil.
[0046] FIG. 2 shows a cross section through the cornea 2 of a human
eye in which a corneal implant 2 according to the invention is
inserted, including markings of the different effective areas of
the cornea 1. The central corneal area 7, which is defined by the
size of the implant 2, is not directly involved in the visual
process. The peripherally adjoining area 8 shows the aspherical
surface contour with the resulting property of multi-focal imaging.
Then comes the corneal area 9 that remains unaffected by the
corneal implant 2.
[0047] Depending on the dimensions of the corneal implant 2, there
is the possibility to add refractive power for near vision to the
area 8, whereas area 9 is intended for far vision. The latter is
peripherally confined by the pupil diameter.
[0048] The embodiment according to FIGS. 1 and 2 presents the use
of a corneal implant 2 which is rotation-symmetrically arranged
around the axis of the effective thickness, thus having the shape
of a sphere and being limited to 1 mm diameter in size. As far as
the aspherical surface contour 3 of the cornea 2 and the
multi-focal imaging properties are concerned, such a sphere-shaped
corneal implant 2 produces exceptionally positive results.
[0049] To the expert it is clear, however, that a corneal implant 2
according to the invention may basically have any shape and yet be
capable of solving the task underlying the invention, provided the
implant has a minimum effective thickness of 50 .mu.m, measured in
the direction of the optical axis 5 of the eye, and a maximum width
of 1 mm, measured in a plane perpendicular to the direction of
thickness.
[0050] It is important to note that due to the introduction of a
corneal implant 2 into the optical centre of the cornea 1, the
curvature R of the cornea around the optical centre changes
significantly.
[0051] The ratio between the width and the effective thickness of
the corneal implant should ideally not exceed factor 3 and/or fall
below factor 1 to assure acceptable multi-focal imaging properties
for the patient. Another requirement is that the width alongside
the circumference must not vary by more than 30 percent of the
largest width.
[0052] FIG. 3 shows a cross section through a corneal implant 2
according to the invention, which has an elliptic cross section
with an effective thickness d and a width b.
[0053] FIG. 4 shows a cross section of an alternative corneal
implant 2 according to the invention, with which the same effect in
keeping with the invention may be achieved as with the corneal
implant 2 depicted in FIG. 3, as long as a minimum effective
thickness of 50 .mu.m and a maximum width of 1 mm as indicated
above are observed. The expert immediately notices that while
cavities, such as those schematically represented in FIG. 4, reduce
the thickness of the corneal implant 2 to a minimum thickness 6 in
some sections, the effective thickness d remains unaffected
therefrom and thus the effect to be achieved according to the
invention is not impacted. Consequently, a corneal implant 2 as
depicted in FIG. 4 allows to change the curvature R of the cornea 1
in the optical centre of the cornea 1, while at the same time
leaving the vision unimpaired.
[0054] FIG. 5a to 5s show further potential cross sections of
corneal implants 2 according to the invention which, provided that
they fulfill the requirements regarding a minimum effective
thickness and a maximum permissible width, support the aspherical
surface contour 3 of the cornea 1 required for multi-focal
vision.
[0055] The invention is based on the assumption that a deflection
of the cornea 1 is required in order to achieve the desired effect,
i.e. the outside measurements of the corneal implant 2 as well as
its elasticity need to be adjusted to the elasticity of the cornea
1 and the compression inside the tissue in such a way that the
desired deflection and the related aspherical surface contour 3 is
achieved. This can be accomplished by using a corneal implant with
an effective thickness of more than 50 .mu.m; by limiting the width
to below 1 mm, a relevant vision impairment and a nutrition
deficiency of the cornea can be prevented and the implantation into
the optical centre can be achieved.
[0056] The material used for the implant may be any type of
biocompatible material such as PMMA, HEMA, acryl-containing
materials, plastics, metals, semi-conductors, insulators, or other
materials commonly used in this field of application.
[0057] The method for producing an implant bed does not differ from
the known techniques. The implant bed may, for example, be produced
by using a LASIK keratome, by cutting a largely enclosed corneal
pocket, as described in EP 1 620 049 B1, or by creating a narrow
corneal tunnel.
[0058] The corneal implant 2 according to the invention primarily
serves to correct a presbyopic condition, but also presbyopia in
combination with hypermetropia. It may also be introduced in
combination with other known corneal implants, for instance in
combination with ring implants as shown in FIG. 6, by which
presbyopia in combination with myopia can be corrected.
[0059] FIG. 6a-b show a known ring-shaped corneal implant 10 which
is implanted outside the optical centre of the cornea 1, as well as
a corneal implant 2 according to the invention which is implanted
in the optical centre of the cornea 1, producing the aspherical
surface contour 3. Instead of a ring-shaped corneal implant 10,
also individual small implants 11, as shown in FIG. 7a-b, may be
applied outside the optical centre of the cornea 1.
[0060] The corneal implants 2 and 10 or 11 together serve to
correct presbyopia in combination with myopia due to the change of
curvature of the corneal surface, even though the implants have no
optical effect.
[0061] In FIG. 7, the small implants 11 are arranged along a
circular line 12 around the optical centre. If the small implants
11 have different sizes, in addition to presbyopia and myopia also
astigmatism may be corrected.
[0062] If the corneal implants 2 and 11 are arranged as illustrated
in FIG. 8 so that a preferred axis 13 is created, also astigmatic
vision may be corrected.
[0063] Due to the complex curvature of the corneal surfaces in
FIGS. 6,7 and 8, the surface is only schematically represented,
without the curvature being changed by the corneal implants 2, 10
and 11.
[0064] It needs to be noted in particular that elements of
embodiments according to the invention may be combined with
elements of other embodiments according to the invention, and that
these combinations again represent embodiments according to the
invention.
* * * * *