WO1999063912A1

WO1999063912A1 - Method and apparatus for insertion of a corneal ring

Info

Publication number: WO1999063912A1
Application number: PCT/US1999/012552
Authority: WO
Inventors: Joseph Y. Lee
Original assignee: Microoptix, Llc
Priority date: 1998-06-08
Filing date: 1999-06-04
Publication date: 1999-12-16
Also published as: AU4420299A

Abstract

This invention relates to a method and apparatus for implanting a corneal ring into the peripheral corneal stroma of the eye. The apparatus employed is an annular instrument (20) comprising a hollow body, a handle (21) located at the rear end of the hollow body, and a leading end (22) at the front end of the hollow body. The corneal ring is inserted into the hollow body of the instrument and implanted into the corneal stroma in an encircling relation to the central optic zone of the cornea. After the instrument has been fully inserted into the peripheral corneal stroma, the corneal ring is immobilized and the instrument is removed.

Description

METHOD AND APPARATUS FOR INSERTION OF A CORNEAL RING

FIELD OF THE INVENTION This invention relates to a method and apparatus for inserting into the corneal stroma of an eye a corneal ring.

BACKGROUND OF THE INVENTION

This invention is a surgical device for inserting into the peripheral corneal stroma of the eye a split corneal ring. The instrument allows for greater ease of insertion of a corneal ring, in particular, a flexible adjustable corneal ring.

Ametropia, an undesirable refractive state of the eye, has three main subdivisions: myopia, hyperopia, and astigmatism. In myopia, by far the most common type of ametropia, the parallel light rays 1 which enter the eye as shown in FIG. 1(a) come to a focus F3 in front of the retina 2 as shown in FIG. 1(c). In hyperopia, the rays of light 2 come to a focus F2 behind the retina 2 as shown in FIG. 1(b). When the rays of light converge to not one, but several foci, it is referred to as astigmatism, in which condition the various foci may all lie before the retina; all lie behind the retina; or partly before and partly behind the retina. Controversy has always surrounded the use of surgical procedures to correct refractive errors of the eye. Because of the risks inherent in surgical intervention, some have argued that no refractive error correctable by spectacles or contact lenses warrants such procedures. Until an ideal refractive procedure is developed, disagreement will persist among ophthalmologists as to which eyes and which patients are appropriate for refractive surgery. The ideal keratorefractive procedure for the correction of myopia should permit all the advantages of eyeglasses or contact lenses, namely, being able to correct a wide range of . refractive errors, generating a high degree of predictability and stability such that >95 % of patients achieve 20/20 uncorrected acuity with long-term stability, allowing reversibility or adjustability in the event that the refractive state of the eye changes, being extremely safe with minimal risk of adverse effects on the quality of vision and being cost-effective. The refractive procedure should also have a favorable learning curve. If a technique permits only a small percentage of ophthalmologists to perform and achieve excellent visual results, it is a seriously deficient procedure.

In short, the ideal refractive procedure has the following characteristics: 1) adjustability, 2) predictability/efficacy, 3) quality of vision preservation, 4) reversibility, 5) stability of refractive effect, 6) simplicity of the procedure, 7) safety, and 8) low cost. For over a century, ophthalmologists have searched for a surgical method to permanently correct refractive errors. Over 15 different techniques have been developed and considerable experience gained in both animal and human models. Oftentimes a given refractive surgical technique has unsolved problems such as poor predictability, unstable refractive outcomes, adverse effects on the quality of vision, lack of adjustability and irreversibility. Poor predictability remains the largest unsolved problem in refractive corneal surgery. The main factors that contribute to poor predictability are: 1) variations and inaccuracies inherent with manual surgical techniques and 2) the variable wound healing response to the surgery. Photorefractive keratectomy offers the possibility of reducing the surgical variability of the procedure. However, the variable corneal wound healing response affects the results of photorefractive keratectomy manifesting as regression of refractive effect which can be up to several diopters in amplitude.

For years it has been thought that refractive surgery with intracorneal implants could be used in the correction of myopia or hyperopia. Early techniques included lamellar removal or addition of natural corneal stromal tissue. These techniques required the use of a microkeratome to remove a portion of the cornea followed by lathing of either the patient's or donor's removed cornea. The equipment is complex, the surgical techniques difficult, and most disappointingly, the results quite variable. The current trend in keratorefractive surgery has been toward techniques that are less traumatic to the cornea, that minimally stimulate the wound healing response, and behave in a more predictable fashion. The use of alloplastic intracorneal lenses to correct the refractive state of the eye, first proposed in 1949 by Jose Barraquer, have been plagued with problems of biocompatibility, permeability of nutrients and oxygen, etc.

More recent techniques have focused on minimizing the effects of the wound healing response by avoiding the central cornea. There have been multiple attempts to alter the central corneal curvature by surgically manipulating the peripheral cornea. These rely upon mechanisms first elucidated by J. Barraquer. Since 1964, "it has been demonstrated that to correct myopia, thickness must be subtracted from the center of the cornea or increased in its periphery, and that to correct hyperopia, thickness must be added to the center of the cornea or increased in its periphery." Procedures involving subtraction were called 'keratomileusis' and those involving addition received the name of 'keratophakia'. Intrastromal corneal ring add bulk to the periphery and increasing the thickness of the ring results in a more pronounced effect on flattening of the anterior corneal curvature by "increasing (thickness) in its periphery".

In the Foreword to the textbook, Principles and Practice of Refractive Surgery, Jose Barraquer writes, "As a result of my initial publications, some authors decided to try different methods to modify the shape of the cornea. Punch stromectomy and temporal inclusion of a plastic disk by Krawawicz ( 1960), the use of a trephine by Pureskin ( 1967), soto impronta by Strampelli (1964), molding by Martinez and Katsin (1965), and corneal rings by Blawatkaia (1966) all were tried."

D.S. Zhivotovskii, in USSR patent No. 3,887,846, describes an alloplastic, flat, geometrically regular, annular ring for intracorneal implantation of a diameter that does not exceed the diameter of the pupil. Refractive correction is accomplished primarily by making the radius of curvature of the surface of the ring larger than the radius of curvature of the surface of a recipient's cornea in order to achieve flattening of the central area of the cornea. Surgical procedures for inserting the ring are not described. The principle is simply that either insertion of an intracorneal ring in the corneal periphery or injection of gels in a preformed peripheral circumferential channel will induce flattening of the center of the cornea. A rigid ring or a gel may induce the same qualitative effect. The addition of matter in the corneal periphery will induce an outward bulging of the corneal surfaces around the implant, thus incorporating excess corneal arc length. Consequently, less of the corneal arc will be available for covering the central cornea, which therefore must flatten.

A simple example is helpful in understanding the mechanism by which corneal rings alter anterior corneal curvature. Assume a loose rope R between two fixed points PI and P2 as shown in FIG. 2, which forms a curve, the lowest point 10 being in the middle.

Referring to FIG. 2(b), a weight W placed on the rope between the middle point and one fixed point will cause the central portion of the rope to straighten. It can be seen that the curvature of the rope in the middle 11 has relatively flattened. The cornea 13 demonstrated in FIG. 3 behaves similarly, the two fixed points, PI and P2, analgous to the limbus 12 of the eye and the weight W similar to the intrastromal corneal implant 16 which, when inserted in the cornea in surrounding relation to the corneal central optic zone, causes the corneal fibers to deviate upwards above the implant, and downwards below the implant. In essence, this deviation of the cornea around the peripheral implant caused by volume displacement in the peripheral cornea results in other areas of the cornea relatively straightening as shown at 15 in FIG. 3(b). With removal of part of the implant 17 as shown in FIG. 3(c), it can be seen that the corneal curvature relatively steepens 18.

Simon in U.S. Patent No. 5,090,955 describes a surgical technique that allows for modification of the corneal curvature by inter-lamellar injection of a synthetic gel at the corneal periphery while sparing the optical zone. He does discuss an intra-operative removal of gel to decrease the volume displaced and thus adjust the final curvature of the central corneal region. Simon also describes a method for producing an interlamellar channel. He describes a flat corkscrew delaminator, which is used to carve a circular canal between the two corneal lamellae in which a gel such as a silicon gel is subsequently injected. The corkscrew delaminator consists of a flat wire about 1 mm or less in width and its edges are blunt or rounded, as is its end.

A.E. Reynolds in U.S. Pat. No. 4,452,235 also describes a split ring shaped dissecting member designed to produce a peripheral interlamellar corneal channel to permit implantation of an intracorneal ring. He describes a keratorefractive technique involving a method and apparatus for changing the shape of the optical zone of the cornea to correct refractive error. His method comprises inserting one end of a split ring shaped dissecting member into the stroma of the cornea, moving the member in an arcuate path around the cornea, releasably attaching one end of a split ring shaped adjusting member to one end of the dissecting member, reversibly moving the dissecting member about the path, and thereby pulling the adjusting member about the circular path, made by the dissecting member, withdrawing the dissecting member, adjusting the ends of the split ring shaped adjusting member relative to one another to thereby adjust the ring diameter to change the diameter and shape of the cornea and fixedly attaching the ring's ends by gluing to maintain the desired topographical shape of the cornea.

Siepser (U.S. Pat. No. 4,976,719) describes another ring-type device to either flatten or steepen the curvature of the cornea by using a retainer ring composed of a single surgical wire creating a ring of forces which are selectively adjustable to thereby permit selective change of the curvature of the cornea, ~ the adjustable means comprising a turnbuckle attached to the wire.

Barrett et al in U.S. Patent No. 5,391,201 describes a corneal inlay ring apparatus for altering the curvature of the central optic zone of the cornea comprising a continuous ring such that the curvature of the anterior cornea is flattened to the extent appropriate to the refractive correction desired. Intracorneal rings have several advantages over photorefractive keratectomy (PRK) including leaving the central cornea intact, reversibility, rapid and stable effect and minimal wound healing responses. However, predictability is still an issue and there is no simple way of adjusting the refractive outcome, aside from explanting the intracorneal ring and replacing with another ring of different size.

A method of adjusting an intracorneal ring thickness after the ring has been implanted in a simple and minimally invasive fashion is described by the present inventor in pending U.S. Application 08/671,362, which disclosure is incorporated herein by reference. That application describes a method and apparatus for corneal curvature adjustment. The method involves inserting a flexible corneal ring, comprised of a hollow ring-shaped shell filled with solid biocompatible material, into the periphery of the cornea. The peripheral corneal volume displaced by the ring can thereafter be adjusted by removing the strand-like solid material from within the shell and thereby decreasing the volume displaced.

However, there has been very little research investigation in the area of flexible corneal rings. Research in the area of corneal rings has focused almost exclusively on solid polymethylmethacrylate rings. There has been little investigation in this area because flexible corneal rings were more difficult to insert and there were no obvious advantages to flexibility. The adjustable corneal ring described in U.S. Patent Application 08/671,362, which is included herein by reference, describes a flexible ring which has a definite advantage over a rigid ring. Therefore, there remains a need for a surgical technique which can ease the insertion of a flexible corneal ring into the peripheral corneal stroma and there remains a need for such a technique wherein the surgical equipment is relatively inexpensive and only moderate surgical skills are required.

SUMMARY OF THE INVENTION The present invention is a surgical device for inserting a corneal ring into the peripheral corneal stroma. The instrument is comprised of a body, which is in the shape of an annular tube with a hollow interior and a handle portion used to guide the body portion of the instrument into the peripheral cornea. The hollow interior of the body portion of the instrument is similar in shape to the corneal ring. The corneal ring is placed within the hollow interior of the instrument. The instrument is then rotated into the corneal stroma in a lamellar fashion. When the leading end of the instrument has been inserted to approximately 360 degrees, the corneal ring within the hollow interior of the instrument is maintained in position while the instrument is reversibly rotated and thus removed from the cornea, leaving the corneal ring in place within the stroma of the peripheral cornea.

Other objects, features, and characteristics of the present invention, as well as the methods of operation, and the combination of parts of manufacture, will become more apparent from a consideration of the ensuing description, the appended claims, and the accompanying drawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic representation of a horizontal section of the human eye; FIG. 1(b) is a schematic representation showing how the light rays focus behind the retina of the eye in the condition of hyperopia;

FIG. 1(c) is a schematic representation showing how the light rays focus in front of the retina of the eye in the condition of myopia;

FIG. 2(a) is a schematic illustration for showing a rope suspended at its ends between two fixed points;

FIG. 2(b) is a schematic illustration which shows the rope in FIG. 2(a) with the force of a weight applied to the rope between its midpoint and one of the fixed points;

FIG. 3(a) is a schematic illustration showing the cornea of an eye wherein the cornea is fixedly attached at diametrically opposed points on the surrounding limbus; FIG. 3(b) is a schematic illustration similar to FIG. 3(a) but showing the curvature effects produced on the cornea because of the presence of an intrastromal support implant in the cornea; FIG. 3(c) is a schematic illustration similar to FIG. 3(b) but showing steepening of the corneal curvature following removal of a portion of the intrastromal support implant from the cornea;

FIG. 4(a) is a perspective view of the surgical instrument of the invention; FIG. 4(b) is a plan view of the surgical instrument of the invention;

FIG. 4(c) is a perspective view of the surgical instrument as taken along the section line 4b — 4b in FIG. 4(b);

FIG. 4(d) is a radial cross-sectional view of the surgical instrument;

FIG. 5(a) is a perspective view of the surgical instrument of the invention; FIG. 5(b) is a perspective view of the surgical instrument of FIG. 5(a) partially inserted into the radial incision of the cornea;

FIG. 6(a) is a perspective view of the surgical instrument with a leading segment attached to the leading end of the instrument;

FIG. 6(b) is a plan view of the surgical instrument of FIG. 6(a) with a leading segment positioned at the leading end of the instrument;

FIG. 7(a) is a plan view of the surgical instrument almost completely inserted into the intrastromal annular lamellar channel of the cornea;

FIG. 7(b) is a plan view of the instrument of FIG. 7(a) partially removed from the cornea of the eye and the corneal ring partially positioned within the lamellar channel of the cornea;

FIG. 7(c) is a plan view of FIG. 7(b) after the instrument has been completely removed, the ring in position within the intrastromal annular channel of the cornea, and the leading segment removed from the corneal ring;

FIG. 8(a) is a radial cross sectional view of the line 7b — 7b from FIG. 7(b) which shows the instrument within the lamellar channel and the flexible corneal ring within the instrument; FIG. 8(b) is a radial cross sectional view of the line 7c — 7c from FIG. 7(c) which shows the flexible corneal ring within the lamellar channel of the cornea;

FIG. 9(a) is a plan view of the instrument containing strands which has been almost completely inserted into the peripheral intrastromal cornea of the eye; FIG. 9(b) is a plan view of the instrument of FIG. 9(a) which has been partially removed from the cornea of the eye and the strands partially positioned within the cornea of the eye;

FIG. 9(c) is similar to the plan view of FIG. 9(b) after the instrument has been completely removed from the cornea of the eye and the strands are in position within the lamellar channel of the cornea;

FIG. 10(a) is a radial cross sectional view of the line 9b — 9b from FIG. 9(b) which shows the instrument within the lamellar channel of the cornea and the strands within the instrument;

FIG. 10(b) is a radial cross sectional view of the line 9c — 9c from FIG. 9(c) which shows the strands within the lamellar channel of the cornea;

FIG. 11 is a perspective view of the surgical instrument with a leading segment attached to the leading end of the instrument;

FIG. 12(a) is a plan view of the leading end of the instrument and the leading segment; FIG. 12(b) is a plan view of the leading end of the instrument and a larger leading segment;

FIG. 12(c) is a plan view of the leading end of the instrument and a leading segment which has positioned an opening within it;

FIG. 12(d) is a plan view of the leading end of the instrument and a leading segment which has an angled design facilitating uni-directional movement;

FIG. 12(e) is a plan view of the leading end of the instrument and a leading segment which fits into the hollow end of the instrument end; FIG. 12(f) is the view of FIG. 12(e) showing the separation of the leading end of the instrument from the leading segment and the attachment of the corneal ring to the leading segment;

FIG. 12(g) is the view of FIG. 12(e) showing the separation of the leading end of the instrument from the leading segment and the attachment of the strands to the leading segment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a surgical device, which provides a technique for inserting a split corneal ring into the mid-peripheral cornea of the eye. The invention is particularly useful for the insertion of flexible corneal rings into the annular lamellar channel of the cornea. The invention comprises a handle, and an annular, hollow body portion. The invention is a surgical device for implanting within a circular, lamellar channel of the corneal stroma an intracorneal ring to correct refractive errors. Prior to insertion of a split corneal ring, an annular lamellar channel must be produced in the mid-peripheral cornea. Methods for producing an interlamellar channel have been extensively described. A.E. Reynolds, in U.S. Patent No. 4,452,235, describes a split- ring shaped dissecting member designed to produce a peripheral interlamellar corneal channel to permit implantation of an intracorneal ring. Simon, in U.S. Patent No. 5,090,955, describes a flat corkscrew delaminator that is used to carve a circular canal between the two corneal lamellae in which a gel such as a silicon gel is subsequently injected. The corkscrew delaminator consists of a flat wire about 1 mm or less in width and its edges are blunt or rounded as is its end.

B. Loomas, in U.S. Patent No. 5,403,335, describes a surgical device for producing a circular, interlamellar pathway within the cornea stroma of the eye. The device is made up of three major components including a vacuum-centering guide, a barrel which fits into the guide, and a circular dissecting ring or dissector. The dissecting ring is shaped in such a way that when the barrel to which the ring is attached is twisted, the ring moves through the interlamellar space in the stroma producing the desired channel or pathway.

The inventor of the subject procedure has filed a U.S. Patent application (July, 1997) entitled, "Corneal circular channel dissecting device", which provides a technique for producing a circular channel within the corneal stroma of the eye. That application is, by reference, included in its entirety within this application. It allows for the formation of an interlamellar channel within the corneal periphery while sparing the central cornea. The surgical technique uses two separate instruments: a channel-guide dissector which is a circular, split-ring dissector with the dissecting end having a slightly blunted tip which allows formation of a narrow lamellar channel and a second instrument which is a wing-shaped lamellar dissector with a tip shaped similarly to the channel-guide dissector thus allowing guidance of the dissecting wing portion into the narrow previously formed lamellar channel. The wing-shaped dissector forms a channel sufficiently wide to allow insertion of an intracorneal ring. The intracorneal ring placed within the created corneal channel alters the shape of the cornea and results in surgical correction of myopia.

A typical approach to forming a mid-peripheral interlamellar annular channel in the cornea is described below. In general, the procedure is performed with only topical anesthesia in cooperative patients. The visual axis is marked by using a sharp instrument to leave an indentation on the epithelium of the cornea. Prior to actual channel formation, an ultrasonic pachymeter is used to measure the corneal thickness at the peripheral cornea where the channel is to be formed. A knife is then used to form an incision at about 2/3 corneal depth to allow introduction of the channeling device. A Suarez spreader or other flat lamellar dissecting blade is introduced into the bottom of this incision and a small lamellar channel created. A vacuum suction ring is then placed over the perilimbal conjunctiva to fixate the globe while the channeling device is introduced through the incision and rotated to produce a 360 degree channel around the corneal mid-periphery at about 2/3 corneal depth. The channeling device is then rotated in the reverse direction and removed from the cornea. The vacuum suction ring is then removed and the split intracorneal ring implanted into the cornea within the annular lamellar channel.

There are two main approaches to the insertion of a split corneal ring into the peripheral cornea. The ring may be "pushed" into the channel or "pulled" into the lamellar channel. Stiffer rings, such as rings made of PMMA, are much more easily pushed into the channel. However, a flexible corneal ring, such as one composed of silicone, is not easily "pushed" into the channel. A flexible corneal ring can be partially "pushed" into the lamellar channel. The flexible corneal ring cannot be further inserted after a few clock hours of insertion because of increased resistance to passage within the lamellar channel and also because the ring's leading end becomes misdirected and catches along the lamellar walls. As described, a relatively flexible corneal ring can only be inserted a short distance into the annular lamellar channel before the flexibility of the ring inhibits forward progress.

If the flexible corneal ring is stiffer or has a supporting structure that adds stiffness, complete insertion within the lamellar channel may be possible by the pushing technique. That supporting structure may be temporary or permanent, inside the corneal ring or outside the corneal ring. The location of a permanent supporting structure is more suitably positioned within the corneal ring. The location of a temporary supporting structure is more suitably positioned outside the corneal ring. The specific advantages of a flexible corneal ring are compromised if the supporting structure that adds stiffness is located within the corneal ring. Ideally, a flexible corneal ring has a temporary supporting structure surrounding the ring and the supporting structure is temporary.

The present invention provides a surgical technique and instrument for inserting a flexible corneal ring into the mid-peripheral annular lamellar channel of the cornea of an eye. In particular, the instrument is a supporting structure that at least partially surrounds the corneal ring and permits the corneal ring to be easily inserted into the lamellar channel. Referring to FIG. 4(a), it can be seen that the surgical instrument used for inserting the flexible ring is circular in shape and can be easily inserted into a previously formed annular intrastromal lamellar channel. The instrument 20 permits delivery of the corneal ring into the lamellar channel. The circular portion or body of the instrument is fashioned such that it is easily inserted into the lamellar channel. The instrument comprises a handle 21, the body of the instrument, and a leading edge 22. The circular portion of the instrument is hollow 27 as can be seen in FIG. 4(c). The leading end 22 of the instrument which is that portion first inserted into the lamellar channel, demonstrates the hollow nature of the circular portion of the instrument. The hollow compartment of the instrument is filled with the corneal ring to be inserted. Ideally, the shape of the hollow compartment complements the shape of the flexible corneal ring to be contained within the instrument.

FIG. 4(c) demonstrates that the radial cross-section of the circular portion of the instrument has a conic angle 28 similar to that of the mid-peripheral corneal. The typical dimensions of the radial cross-section of the instrument are similar to the dimensions of the ring to be inserted. Referring to FIG. 5(b), after placement of the flexible corneal ring within the hollow compartment of the instrument, the instrument is inserted into a pre-formed annular lamellar channel. The leading end of the instrument 22 is inserted through the anterior corneal incision 31. A portion of the instrument 30 within the lamellar channel is illustrated. After complete insertion of the instrument, the corneal ring within the instrument's hollow tube is grasped and the instrument reversibly rotated and removed from the cornea of the eye leaving the corneal ring in position within the lamellar channel of the cornea. Prior to instrument removal, the corneal ring within the instrument's cavity may be grasped or immobilized by various means and then the instrument reversibly rotated and removed from the cornea. FIG. 6(a) demonstrates another aspect of the insertion instrument. It shows the instrument, similar to that previously described. However, the instrument has a leading segment 40. The leading segment 40 is attached to the corneal ring contained within the body of the instrument but is not attached to the instrument. FIG. 7(a) illustrates the instrument 20 with the leading segment 40, completely inserted within the previously formed lamellar intrastromal channel. The handle 21 of the instrument abuts the edge of the radial incision 31. FIG. 7(b) demonstrates partial removal of the instrument 20. The leading segment 40 easily permits forward progress but resists backward movement. Thus, as the instrument is slowly withdrawn, the leading segment maintains its position. Since the leading segment is attached to the corneal ring, the corneal ring 16 is removed from the instrument as the instrument is removed from the cornea. Alternatively, the leading segment may be grasped by a forceps through the radial incision 31 or immobilized by some other means while the instrument 20 is being removed. Sub-embodiments of the leading segments are further described later. The complete instrument is not shown 42 to ease visualization. FIG. 7(c) shows the cornea of the eye after the instrument has been completely removed with the corneal ring in position within the lamellar channel. The leading segment has been removed 43. FIG. 8(a) demonstrates a radial cross-section through line 7(b) — 7(b). It is a cross-sectional view of the cornea at a point where the instrument has been inserted. The instrument 20 can be seen within the lamellar walls 50, 51 of the cornea. The shell 54 of the corneal ring can be seen inside the hollow chamber of the instrument. The strands 55 can be seen within the shell of the ring. The inner 52 and outer 53 diameters of the lamellar channel can be seen.

FIG. 8(b) demonstrates a radial cross-section of line 7(c) — 7 (c) after the instrument has been completely removed, leaving the corneal ring in position within the lamellar channel. Again, the channel walls 50, 51 are illustrated. The shell 54 of the corneal ring contacts the channel walls. The strands 55 add volume and thickness to the corneal ring, causing the upper channel wall 50 and lower channel wall 51 to be separated.

The corneal ring insertion instrument is most suitable for the insertion of . flexible corneal rings. However, the instrument may also be used for various other types of corneal rings. For example, FIG. 9(a) illustrates the instrument of the invention with the leading segment 40 positioned at its leading end inserted within the cornea 13. The instrument in this particular example has contained within its hollow compartment a corneal ring consisting of strands only. The strands can be of various materials as previously described in the author's previously mentioned patents. The strands may be variable in number or size. The radial cross-section of the strands may be of various geometric shapes including, circular, square, rectangular, or other polygon. The combination of strands act as a corneal ring in that the strands cause volume displacement in the peripheral corneal tissue, thus flattening the anterior corneal curvature in the same fashion that rigid corneal rings and rings formed of gel act to flatten the central corneal curvature. Because of the flexibility of a corneal ring device comprised of a combination of strands, it is necessary to provide a special method of insertion or placement of the strands within the lamellar channel of the cornea.

Thus, the corneal ring insertion instrument of the present invention provides a method of easily inserting a device comprised of a combination of annular strands within the mid-peripheral annular lamellar channel of the cornea. It can be seen that the corneal ring insertion instrument is especially advantageous when the corneal ring is flexible or is comprised of several separate strands. However, the insertion instrument may also be useful in the insertion of a rigid PMMA split corneal ring.

FIG. 9(a) demonstrates the instrument of the invention containing the combination of annular strands within its hollow compartment, which has been completely inserted into a previously formed lamellar channel within the cornea through the initial incision 31. Referring to FIG. 9(b), it can be seen that following complete insertion of the instrument within the lamellar channel, the leading segment 40 is immobilized with respect to the surrounding corneal stroma while the instrument is gradually reversibly rotated and thus removed from the cornea. Only part of the instrument is illustrated 42 to ease visualization since a complete drawing of the instrument would cover the leading segment 40. The strands 55 contained within the hollow compartment of the instrument are attached to the leading segment 40. As the instrument is withdrawn, the strands emerge from the hollow compartment of the instrument. FIG. 9(c) shows the placement of the strands 55 within the annular intrastromal corneal channel after the instrument has been completely removed from the cornea. The leading segment has also been removed 60 from the strands. FIG. 10(a) shows a cross-section of the cornea at a point where the instrument containing the combination of strands has been inserted into the lamellar channel. FIG. 10(b) illustrates the position of the strands within the lamellar channel after the instrument has been completely removed from the corneal channel. It can be seen that the strands are maintained in relative proximity to each other by the walls of the lamellar channel 50-53. An aspect of the method that requires further description concerns the process of immobilizing the leading segment after complete insertion of the instrument within the lamellar channel and prior to withdrawing the instrument from the cornea. Again, the leading segment is attached to the corneal ring contained within the body of the instrument but is not attached to the instrument. Also, the leading segment is sized and configured such that at most it may only partially insert into the hollow cavity of the leading end. If the leading segment completely inserted into the hollow cavity while the instrument was placed within the cornea, it would be extremely difficult to grasp the leading segment and remove the corneal ring while the instrument was being withdrawn. Typically, following complete insertion of the instrument containing the corneal ring, the leading segment may be grasped by a forceps or some other means at a point near the initial incision site. However, there are other methods of relatively stabilizing the position of the leading segment while the instrument is removed from the cornea. It is essential that the leading segment maintain its position since the corneal ring will not emerge from the instrument with removal of the instrument unless the leading segment, which is attached to the corneal ring, maintains its position.

The following are various methods to relatively immobilize the leading segment after the instrument has been completely inserted within the lamellar channel. In general, the leading segment may be relatively immobilized after complete instrument insertion by inserting a forceps into the radial incision and grasping the leading segment. FIG. 12(a) demonstrates a leading segment 70 having a square configuration. The leading segment is comprised of a material that is attracted to a magnet. The leading segment is immobilized using a magnet that is positioned anterior to the cornea at a point above the leading segment. In a variation of this method, a coated magnet can be inserted into the initial incision and positioned at the entrance of the lamellar channel near the leading segment and thus maintain the position of the leading segment as the instrument is withdrawn.

FIG. 12(b) shows a leading segment 71 that has a width 72 that is larger than the width 73 of the instrument. Because of the larger size of the segment, following complete insertion, the corneal channel walls will exert pressure on the segment providing resistance to movement such that as the instrument is removed, the leading segment maintains the desired position. FIG. 12(c) illustrates a leading segment 74 that has a hole 75 for easier manipulation. The leading segment may be immobilized by the use of a hooked instrument in this case.

Referring to FIG. 12(d), the leading segment 76 may be designed such that there is little resistance to passage of the leading segment in a forward direction but much more resistance to backwards movement of the leading segment. The posteriorly directed wings 77 add resistance to movement of the leading edge in a backwards direction. In this fashion, the leading segment provides little resistance to passage of the instrument as it is completely inserted. However, upon removal of the instrument, the leading segment maintains its position within the lamellar channel. Since the leading segment is attached to the corneal ring, the corneal ring within the instrument gradually emerges from the instrument as the instrument is removed from the cornea.

FIG. 12(e)- 12(g) illustrates a leading segment 78 that partially inserts 79 into the leading end 22 of the instrument. It can be seen that although the leading segment will only partially inserts into the leading end, it is easily withdrawn from the leading end 20 of the instrument. The corneal ring 16 is attached to the leading segment and withdraws from the hollow cavity of the instrument when the leading segment is separated from the instrument. FIG. 12(g) demonstrates that various types of corneal rings can be attached to the leading segment. In the above described methods, there is a pre-formed intrastromal lamellar channel present prior to insertion of the instrument and implantation of the flexible corneal ring. In a slightly different method, the instrument of the invention can be used to form the channel and implant the corneal ring simultaneously. In this method, the leading segment preferably has a portion that partially inserts into the leading end of the instrument to provide greater stability. The leading segment has a more pointed configuration as in FIG. 11. An incision is made into the peripheral anterior cornea at about 2/3 corneal depth. The instrument with the pointed leading segment is placed at the bottom of the corneal incision and advanced in an annular fashion to provide an intrastromal channel centered about the optical zone of the cornea. After the instrument is completely inserted and the leading segment can be grasped from the initial incision, the instrument is reversibly rotated and removed from the cornea, leaving the flexible corneal ring in place within the newly formed annular intrastromal channel. In yet another variation, a narrow complete annular channel may be formed prior to insertion of the instrument. Various aspects of channel formation are described in this author's previously mentioned U.S. Provisional Patent application, filed July 4, 1997, entitled "Corneal circular channel dissecting device".

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A device for inserting a corneal ring into peripheral corneal stroma comprising: a) an annular, hollow body comprising two ends, a rear end and a front end; b) a handle connected to the rear end of said hollow body; and, c) a hollow leading end located at the front end of said hollow body.

2. A device for adjusting an anterior corneal curvature comprising: a) an annular, hollow body comprising two ends, a rear end and a front end; b) a handle connected to the rear end of said hollow body; c) a hollow leading end located at the front end of said hollow body; and, d) a corneal ring inserted into the hollow body of said device.

3. The device as claimed in Claim 2, wherein said corneal ring further comprises a leading segment attached to said corneal ring.

4. The device as claimed in Claim 3, wherein the corneal ring is inserted into said device so that the leading segment of said corneal ring is positioned at the leading end of said device.

5. The device as claimed in Claim 4, wherein the leading segment of said corneal ring is configured so that the leading segment may only partially insert into the leading end of said device.

6. A corneal ring comprising an annular body and a leading segment attached to an end of said annular body.

7. The corneal ring as claimed in Claim 6, wherein said corneal ring comprises a hollow shell containing a plurality of strands of variable size.

8. The corneal ring as claimed in Claim 7, wherein said plurality of strands are variable in number.

9. The corneal ring as claimed in Claim 8, wherein said strands may have a radial cross-section of various geometric shapes selected from the group consisting of a square, a circle, a rectangle, and a polygon.

10. The corneal ring as claimed in Claim 6, wherein the leading segment of said corneal ring is configured to ease immobilization of the leading segment of said corneal ring after complete insertion.

11. The corneal ring as claimed in Claim 10, wherein said leading segment is designed with posteriorly directed wing-like projections that allow forward motion for insertion, but resist backward movement.

12. The corneal ring as claimed in Claim 10, wherein said leading segment is comprised of a magnetic material.

13. The corneal ring as claimed in Claim 10, wherein said leading segment is designed to have a larger width than the width of a device for inserting said corneal ring.

14. The corneal ring as claimed in Claim 10, wherein said leading segment has a hole for immobilization by use of a hooked instrument.

15. A process for inserting into a peripheral corneal stroma a corneal ring comprising a leading segment attached to the corneal ring using a device comprising: an annular hollow body comprising two ends, a front end and a rear end; a hollow leading end located at the front end of said hollow body; and, a handle attached to the rear end of said hollow body, said process comprising the steps of:

a) placing said corneal ring into said hollow body of said device, positioning the leading segment of said corneal ring with the leading end of said device;

b) making a radial incision into the peripheral anterior cornea;

c) at the bottom of the incision, inserting said leading end of said device;

d) advancing said device in an annular fashion into the corneal stroma approximately 360 degrees thereby forming an annular channel between lamellae of the corneal tissue, said channel extending about an optical zone of the cornea;

e) immobilizing said leading segment of said corneal ring; and,

f) reversibly rotating the device, thereby removing the device.

16. The process claimed in Claim 15, further comprising the steps: a) at the incision, forming an annular channel between lamellae of the corneal tissue said channel extending about an optical zone of the cornea.

17. A process for altering the corneal curvature, said process comprising the steps of:

a) inserting a corneal ring comprising a leading segment into a device, said device comprising: i) an annular, hollow body comprising two ends, a rear end and a front end; ii) a handle connected to the rear end of said hollow body; iii) a hollow leading end located at the front end of said hollow body; and,

b) positioning the leading segment of said corneal ring with the leading end of said device;

c) making a radial incision into the peripheral anterior cornea;

d) at the bottom of the incision, inserting said leading end of said device;

e) advancing said device in an annular fashion into the corneal stroma approximately 360 degrees thereby forming an annular channel between lamellae of the corneal tissue said channel extending about an optical zone of the cornea;

f) immobilizing said leading segment of said corneal ring; and,

g) reversibly rotating the device, thereby removing the device.

8. The process claimed in Claim 17, further comprising the steps: a) at the incision, forming an annular channel between lamellae of the corneal tissue said channel extending about an optical zone of the cornea.