Corneal implant

Surgical replacement of all or a portion of the cornea may be performed through the use of an implant having a central lenticular portion, and a peripheral portion having an outer tissue contacting surface of a biologically compatible material. The peripheral portion protects eye tissue from contact with the lenticular portion.

FIELD OF THE INVENTION 
The invention relates to prosthetic devices, and particularly to such 
devices as may be employed to replace damaged corneal tissue. 
BACKGROUND OF THE INVENTION 
For various reasons, the corneal portions of eyes must be surgically 
replaced. For example, the cornea may become scratched or scarred or 
otherwise physically damaged, greatly hindering sight. The cornea is also 
subject to affect by various degenerative diseases, mandating replacement 
if the patient is to have normal or even near normal vision. Corneal 
transplants have become quite common in the United States, particularly 
with the advent of microsurgery. Unfortunately, donor corneas are very 
difficult to obtain. A cornea to be donated must be employed, if at all, 
within a matter of days or weeks from the time of death of the donor. 
Although eye banks have been organized throughout the United States, one 
cannot rely upon the availability of a donor at the time it is needed for 
a transplant operation. As a result, vision, which could have been wholly 
or partially restored in many patients, is often permanently lost. 
DESCRIPTION OF THE PRIOR ART 
Attempts have been made in the past to utilize artificial materials for 
corneal transplants. Representative of such attempts are those reported in 
Barraquer, Queratomileusis y Queratofaquia, Instituto Barraquer de 
America, Bogata, Col. 1980, and Yasuji, Research on Transplantation of 
Cornea Artificialis, Proc. Japan Opthal. Soc. 1950 (Abstract). For the 
most part, the implantation of artificial corneal materials has at best 
been a temporary, stop-gap measure taken to seal the anterior chamber of 
the eye for a period of time until a donor cornea could be located for 
transplantation. As with other parts of the human body, the eye tends to 
reject and eject or extrude foreign materials during the healing process, 
with the result that the implantation of artificial corneas generally 
leads to loss by ejection of the cornea, to further eye damage and to 
leakage of aqueous humor from the anterior chamber. 
SUMMARY OF THE INVENTION 
In one embodiment, the invention relates to an implantable corneal 
prosthesis which comprises a lenticular transparent central portion of a 
biologically acceptable material, and a peripheral portion having an 
outer, tissue-contacting surface of a material that is biologically 
compatable with the eye tissue contacted by it after implantation. The 
peripheral portion is configured to protect the lenticular portion from 
contact with eye tissue. Attachment means are preferably provided for 
attaching the ring to the rim of tissue remaining after surgical removal 
of all or a portion of the cornea from the eye. In the preferred 
embodiment, the tissue-contacting surface of the peripheral portion is of 
a material, such as gold, platinum, polymers or other material that is not 
only biologically compatable but which in addition supports the adherence 
of the adjacent eye tissue thereto. 
In another embodiment, the invention relates to a method of surgical 
placement of an artificial cornea in an eye which comprises the steps of 
removing all or a portion of the natural cornea from the eye, leaving a 
generally circular rim, providing an implantable corneal prosthesis having 
a lenticular, central portion, and a peripheral portion having an outer, 
tissue-contacting surface of a material that is biologically compatable 
with the rim of eye tissue, the periphery being configured to protect the 
disc from contact with the corneal tissue of an eye and including 
attachment means for attaching the ring to the rim of eye tissue, and 
placing the prosthesis centrally within the rim of tissue and attaching 
the attachment means to and within the rim of tissue. 
In a preferred embodiment, the attachment means comprises a flange or 
flanges extending outwardly of the prosthesis generally parallel to the 
surface of the eye wall adjacent the tissue rim. The method desirably 
includes the step of inserting the flange means laterally within the 
thickness of the rim so that the flange or flanges are substantially 
completely imbedded in the thickness of the rim, preferably within the 
anterior two-thirds of such thickness. This may be accomplished by 
stretching the rim slightly during the surgical placement of the 
prosthesis. This may also be accomplished by removing a partial thickness 
annular section of cornea or scleral tissue from the rim, placing the 
prosthesis device within the opening with its outwardly extending flange 
or flanges resting upon the remaining thickness of the rim, and then 
replacing the removed annular section upon the flange or flanges. Suturing 
is provided, as necessary. It will be understood that the entire 
tissue-contacting surface of the prosthesis, including the attachment 
means, is of a biologically acceptable material which is not subject to 
rejection or ejection by eye tissue and which will support the adherence 
of eye tissue thereto as the healing process proceeds. 
In each of the embodiments of the invention, the peripheral portion of the 
prosthesis serves as a barrier between tissue of the adjacent tissue rim 
and the generally transparent lenticular portion; that is, by employing a 
peripheral portion having a tissue-contacting surface that is not ejected 
or rejected by the eye, the lenticular portion of the prosthesis is 
maintained out of contact with the tissue corneal rim and no ejection or 
rejection of the prosthesis as a whole occurs. During the healing process, 
ingrowth of the rim tissue onto the peripheral outer surface more securely 
holds the prosthesis in place.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIGS. 1-3, a device of the invention is shown generally 
as (10) and includes a central transparent lenticular portion (14) and a 
peripheral portion typified by a ring or circular frame (12). The 
prosthesis may be mounted in the eye as a corneal replacement as shown in 
FIGS. 8-12, the peripheral portion (12) spacing the lenticular portion 
(14) from the eye tissue and having a biologically compatible outer 
surface (12.2) that solely is in contact with eye tissue. 
By "biologically compatible," reference is made to materials that are not 
ejected from eye tissue nor provoke immune responses, all as described 
more fully below. One such material is substantially pure gold. Platinum 
and certain silicones may also be biologically compatible. Desirably, the 
outer, tissue-contacting surface also supports the growth of eye tissue 
thereon; exemplary of such materials is substantially pure gold and alloys 
of high gold content, and the surface preferably is burnished. The choice 
of a biologically acceptable material may depend upon the portion of the 
eye wall to which it is to be attached, in that the corneo-scleral portion 
of the eye appears to be more tolerant of foreign material than the 
peripheral corneal area which in turn is more tolerant than the central 
corneal area. 
The biological compatibility of the peripheral surface of the prosthesis is 
of great importance in the substantially permanent acceptance of the 
prosthesis by the eye, and provides a strong, liquid-tight seal between 
the prosthesis and the eye wall to seal the anterior chamber. 
As shown in FIGS. 2-4, the ring (12) may have a generally rectangular, or, 
preferably, a parallelogram configuration in cross-section, the inner 
periphery of the ring being generally perpendicular to its plane so as to 
provide surface-to-surface contact with the outer periphery of the 
disc-like lenticular portion (14). Similarly, the outer periphery (12.2) 
of the ring preferably also is generally perpendicular to the plane of the 
ring so as to provide generally surface-to-surface contact between it and 
the generally flat edge "E" (FIG. 12) of the rim of tissue remaining after 
surgical removal of all or a portion of the cornea. Other cross-sectional 
configurations, of course, can also be employed. 
As shown in FIG. 4, the ring may have an inwardly protruding rim (12.3) 
forming an annular shoulder at one edge of the ring upon which the 
periphery of the disc (14) may seat when the ring (12) and disc (14) are 
assembled. 
The thickness of the ring is desirably chosen to be approximately the same 
as the thickness of the corneal tissue to which it is to be attached. The 
thickness of the ring (measured radially of the prosthesis) is sufficient 
to provide the ring with resistance to deformation from the forces 
encountered during implantation. 
The disc-like lenticular portion (14) may be made of any substance that is 
biologically acceptable (that is, that does not introduce harmful foreign 
substances into the eye), and the preferred material is polymethyl 
methacrylate. The disc desirably has a slightly domed outer surface (14.1) 
to simulate the natural curvature of the surgically removed corneal 
portion. Its interior surface (14.2) may be configured as desired, and may 
be generally planar as shown in the drawings or slightly concave if 
desired. Also, the disc may be so configured as to act as a lens and to 
provide a visual correction for the eye. The outer periphery (14.3) of the 
disc desirably is generally flat so as to provide surface-to-surface 
contact between it and the ring. If desired, the edge of the disc may be 
recessed slightly as shown at (14.4) in FIG. 4 to receive the rim (12.3) 
of the ring. 
The disc (14) desirably is adhesively attached within the ring (12), and 
various biologically acceptable adhesives such as dental adhesives are 
known. The adhesive may be employed between the mating surfaces of the 
ring and disc, the adhesive being chosen not only for its bonding 
properties, but also for its biological acceptability. The adhesive should 
be resistant to aqueous humor and to tear fluid, and should not contain 
materials that might be leached from the prosthesis. The disc may be 
mechanically attached to the ring by means of the rim (12.3), as described 
above, and also by means of bendable fingers or prongs (12.4) shown best 
in FIG. 4, the fingers arising from the inner periphery of the ring and 
being bent over into contact with the upper surface (14.1) of the disc 
when the disc and ring are assembled. Desirably, a plurality of fingers 
(12.4) are employed and are spaced equiangularly about the periphery of 
the ring. It will be understood that although a preferred configuration 
and means of attachment of the ring and disc have been described, various 
other configurations and means of attachment may be employed in this 
preferred embodiment as well. It is required that the attachment between 
the ring and disc be strong, reliable and leak-proof. 
Attachment means, typified as outwardly extending tabs or flanges (12.5), 
are employed as part of the peripheral portion of the prosthesis to mount 
it to the rim of an eye from which at least a portion of the cornea has 
been removed. The flange or flanges (12.5) preferably extend generally 
radially outwardly from the outer periphery (12.2) of the ring 
intermediate its height and parallel to the curvature of the eye portion 
to which they are attached; that is, the flange or flanges are formed at 
an oblique angle to the axis of the lenticular portion. The flanges are 
spaced, desirably equiangularly, about the periphery of the ring. In the 
embodiment shown in FIGS. 1-3, the flanges have a thickness preferably 
less than one-third of the thickness of the tissue rim to which the ring 
is to be attached. The flanges may be generally rectangular when viewed 
from the top, as in FIG. 1, or may be of any other appropriate 
configuration. For example, the flanges (12.5') may be generally dumbbell 
in shape (FIG. 6A) or may be formed of small wire loops (FIG. 6B) (12.5") 
extending outwardly from the outer periphery (12.2) of the ring. The 
flanges extend outwardly from the ring for a distance sufficient to enable 
them to be sufficiently deeply embedded within the thickness of the tissue 
rim as to securely hold the ring in place. Six flanges, equiangularly 
spaced about the periphery of the ring as shown in FIG. 1 are preferred, 
although more or fewer flanges may be employed as desired. Also, it will 
be understood that the use of a plurality of flanges as described above 
represents a preferred means of attachment of the ring to the tissue rim 
of an eye; other means of attachment may also be employed. For example, a 
single, continuous thin flange (12.5'") suitably perforated to receive 
stitches or to promote tissue ingrowth or both, is shown in FIG. 7. 
As explained briefly above, the peripheral, tissue-contacting surface of 
the prosthesis is of a biologically compatible material such as gold, 
alloys of high gold content, and other inert materials. Except for the 
usual symptoms of trauma immediately following implant surgery, the eye 
should not become inflamed nor should cloudiness or vascular ingrowth of 
the remaining corneal portion develop, nor should iritis occur, nor should 
the prosthesis show a tendency to migrate anteriorly or posteriorly of its 
original implanted position. Desirably, the material forming the 
tissue-contacting surface of the peripheral portion should support tissue 
adherance to it during the healing process. The characteristics of certain 
materials implanted in living tissue have been reported in Venable et al., 
A General Consideration of Metals for Buried Appliances in Surgery, 
International Abstract of Surgery 76:297-304 (1943); Wolkowicz, et al., 
Gold Leaf Seton for Lowering Intraocular Pressure, Annals of Opthalmology, 
May, 1971, pp. 527-541, and Bick, Use of Tantalum for Ocular Drainage, 
Archives of Opthalmology 42:373-388 (1949). The most biologically 
compatible materials generally are opaque. 
The surgical methods which are employed for implantation of the prosthesis 
of the invention are to be very carefully performed, often through the aid 
of a microscope as is the case with surgical procedures involving donor 
corneal transplants, nerve reattachments and other types of microsurgery, 
and the preparations for surgery and the surgical tools employed in the 
method of the invention are identical or similar to those employed in 
donor corneal transplant surgery. 
Prior to surgery, the diameter of the corneal section to be removed from 
the eye is determined so that the diseased or damaged portion of the 
cornea may be removed while leaving a sufficient amount of corneal or 
corneo-scleral rim material to enable the prosthesis of the invention to 
be implanted. Also prior to surgery, the prosthesis of the invention is 
made ready for implantation by suitable sterilization procedures. If 
desired, the prosthesis may be fabricated at or shortly prior to the time 
of surgery so that the correct sizing to the individual patient may be 
accomplished. The diameter of the peripheral portion (12) measured across 
its outer periphery (12.2), should be the same as or slightly larger than 
the diameter across the tissue rim remaining after removal of the corneal 
portion. Should the patient be a child, care is generally taken to make 
the diameter of the corneal rim as small as practicable so that, as the 
child grows, the prosthesis of the invention may be replaced with larger 
prostheses while still maintaining the field of the implant within the 
bounds of the corneo-scleral limbus, subsequent implant procedures 
ordinarily involving the removal of a small portion of the previously 
formed corneal rim. 
In the implant procedure, the eye is immobilized and the corneal portion to 
be removed ("B") is excised employing a trephine "T" of the type normally 
used in corneal transplant procedures. In FIGS. 8-15, "E" represents the 
eye of a patient, "L" represents the corneo-scleral limbus, "C" represents 
the cornea, "R" represents the rim of the cornea remaining after the 
removal of the portion ("B"), and "P" (in FIGS. 9 and 11) represents the 
unaffected pupil of the eye. 
Upon completion of the total penetrating keratectomy, the prosthesis of the 
invention is inserted into the circular space defined by the rim "R", the 
flanges (12.5) (normally having sharpened ends) being pushed into and 
becoming imbedded within the thickness of the tissue rim. During the 
procedure, the prosthesis is supported by a suitable handle or grip such 
as a small suction cup (not shown) applied to the outer, domed surface of 
the disc. Care is taken that each of the flanges (12.5) are thus inserted 
preferably between the posterior one-half and the anterior one-third of 
the thickness of the tissue rim. Desirably, small sutures ("S" in FIGS. 11 
and 12) are taken about each flange and are passed through the cornea to 
anchor the flanges in place. The generally tight fit between the 
peripheral portion and the tissue rim assures that no leakage of aqueous 
humor from the eye will occur. Post-operative procedures are those 
commonly employed in corneal transplant surgery. It will be noted that the 
small fingers (12.4) which, in the embodiment of FIG. 4, aid in holding 
the disc permanently in place within the ring, are quite thin and are 
feathered toward their outer edges so as to provide minimal irritation to 
the highly sensitive inner lining of the eyelid. 
FIGS. 13-15 show a modification of the procedure described above. Upon 
removal of a corneal portion "B" as shown in FIG. 9, the surgeon 
additionally removes a partial thickness annular ring "A" from the outer 
periphery of the rim "R". In this embodiment, the prosthesis is then 
gently placed in the rim with the flanges (12.5) resting downwardly 
against the shoulder "SH" formed by removal of the annular portion "A". 
The annular portion is then replaced and is sutured to adjacent corneal 
material by sutures "T" (FIGS. 14 and 15). This procedure may involve less 
trauma to the rim of tissue and assures proper placement of the flanges 
(12.5) in the thickness of the corneal rim, as shown in FIG. 14 and as 
described above. 
Various other embodiments will now become evident to those skilled in the 
art. For example, to improve the liquid-tight seal between the peripheral 
portion (12) and the tissue rim to which it is affixed, following the 
procedure depicted in FIGS. 13-15, the peripheral portion of the ring may 
be provided with a generally downwardly facing, annular shoulder (12.7) 
shown in FIG. 16 which contacts and rests upon the shoulder "SH" formed in 
the tissue rim by removal of the annular portion "A". 
Although the above discussion has referred for the most part to prosthesis 
in which the peripheral portion comprised a structural ring of gold or the 
like, it will now be understood that only the tissue-contacting outer 
surface of the prosthesis need be of a biologically compatible periphery 
of the prosthesis may in fact be quite thin and may be applied to the 
peripheral edge of a lenticule by use of an adhesive, by electroplating or 
by other methods. The application of gold leaf to various materials is 
known, for example. FIG. 18 depicts a preferred embodiment of the 
invention in which the lenticular portion (14) is formed with one or more 
flanges (14.5) of the type described above, the eye-contacting periphery 
of the lenticule bearing a thin coating (12.8) of gold or other 
biologically acceptable material. The coating preferably not only covers 
the actual tissue-contacting surface, but also extends inwardly of the 
periphery of the device a short distance, as shown in FIG. 18 and also 
FIGS. 19 and 20. Either the peripheral portion (12) or the lenticular 
portion (14), or both, should be sufficiently strong as to provide the 
prosthesis with resistance to undue bending or tearing. Although the 
prosthesis may be slightly flexible, it is desired that particularly the 
lenticular portion (14) be substantially rigid or at least semi-rigid. 
As mentioned above, the penetrating keratectomy commonly provides the 
remaining rim of tissue with walls generally parallel to the visual axis 
of the eye, and the peripheral exterior tissue-contacting surface of the 
prosthesis is commonly parallel to the axis of the lenticular portion 
(excluding the flanges (12.5), (14.5)) to provide surface-to-surface 
contact with the tissue walls. If desired, however, the tissue-contacting 
surface of the prosthesis may be provided with other configurations to 
best suit the particular tissue rim. If the rim of tissue is particularly 
thick, for example, one may desire to use a prosthesis with a generally 
convex or outwardly rounded periphery, as shown in FIG. 19. Similarly, one 
may wish to employ a prosthesis having a concave or grooved periphery as 
shown in FIG. 20 if the tissue rim is particularly thin. 
In FIG. 17, which diagrammatically depicts the anterior portion of the 
human eye, the cornea is represented as "C", the sclera (and associated 
structures such as the conjunctiva, Tenons (Capsule, epischlera and 
choroid, not separately shown) by "SCH", the iris by "I", the ciliary body 
by "CB" and Schwabe's Line by "SL". Three proposed locations of the 
prosthesis are shown. In the first, only the central corneal "button" is 
removed and replaced by the prosthesis; dashed line "CC" locates the 
boundary of the keratectomy. In the second, the boundary of the 
keratectomy is in the peripheral corneal area and is designated "PC". In 
the third, boundary of the keratectomy is adjacent the limbo-scleral ring 
"LSR" in the corneo-scleral portion of the eye and is designated "CS". To 
avoid damage to the aqueous humor drainage mechanism, it is recommended 
that the internal boundary of the keratectomy not be carried posteriorly 
of Schwabe's Line "SL", although the flange (12.5) may project as desired 
into the sclera. 
Each position shown in FIG. 17 has certain advantages and disadvantages. 
For example, replacement of the central corneal button may limit 
peripheral vision slightly and the risk of failure of the operation is 
increased; yet, assuming that the corneal rim is not damaged, this 
location may permit subsequent implant or transplant procedures to be 
performed. The corneo-schleral position appears least likely to fail and 
may be cosmetically superior, but such position severely limits repeat 
implants or transplants. 
The prosthesis and method of the invention may be employed not only as a 
temporary, sealing, visionproviding measure while the availability of a 
natural donor cornea is awaited, but also as a permanent implant, 
particularly with older patients or for patients unable, because of immune 
reactions, to tolerate donor corneas. As mentioned above, the lenticular 
portion (14) may function as a lens for the purpose of correcting vision, 
and may be particularly valuable as a replacement for a natural lens that 
has been removed through cataract surgery. 
While a preferred embodiment of the present invention has been described, 
it should be understood that various changes, adaptations and 
modifications may be made therein without departing from the spirit of the 
invention and the scope of the appended claims.