WO1999020188A1

WO1999020188A1 - In situ internal refractive corneal reshaping

Info

Publication number: WO1999020188A1
Application number: PCT/US1998/022207
Authority: WO
Inventors: Eugene Gordon; Parid Turdiu; Barbara Parolini; Richard J. Redpath
Original assignee: Medjet, Inc.
Priority date: 1997-10-22
Filing date: 1998-10-22
Publication date: 1999-04-29
Also published as: AU1361999A

Abstract

A method, and device for the selective internal reshaping of corneal tissue to provide refractive corrections. The device comprises a high speed controlled water jet, and a specifically shaped compression template. The cornea is selectively compressed by the template to provide local areas of compression corresponding to areas of the cornea necessary for removal for refraction correction. With the template in place, a high speed pressurized water jet is used to enter the corneal tissue (5) (through a preformed aperture (31) in the corneal tissue), to laterally erode (i.e., remove) tissue under compression, and to laterally cleave but otherwise not remove tissue not under compression. The water jet removes eroded tissue. The compression template causes corneal tissue to fill the area of eroded tissue, and to thereby controllably internally reshape the cornea.

Description

IN SITU INTERNAL REFRACTIVE CORNEAL RESHAPING FIELD OF THE INVENTION

This invention relates to methods and devices utilized in corneal reshaping for vision correction and particularly to the use of waterjets for effecting such corrections.

BACKGROUND OF THE INVENTION Various surgical methods and procedures for vision correction have generally involved reshaping of the cornea by removal of corneal tissue from an exposed portion of the cornea. These procedures include corneal tissue removal by means of an ablative excimer laser which successively removes thin corneal tissue layers to effect the reshaping.

Corneal tissue removal by the excimer laser is either done by direct application against the outer corneal tissue layers, photorefractive keratoplasty, PRK, or more preferably, to preserve the Bowman's layer, in conjunction with a surgical procedure known as Automated Lamellar Keratoplasty (ALK) . This procedure, known as LASIK, involves an initial surgical removal, with a microkeratome, of a uniform thickness button or lenticule of corneal tissue of a thickness containing the epithelium layer, Bowman's membrane (intact) and a portion of the stroma. The button or lenticule preferably remains hingedly attached to the cornea, as a flap, in a region adjacent to the perimeter of the flap. The lenticule is moved out of the way, the stroma bed is then surgically reshaped using PRK, as required, and the lenticule is replaced, with adherence and healing of the stroma- stroma surfaces and with the Bowman membrane being preserved, leaving the cornea relatively clear. The patient can see almost immediately after the surgery since the epithelium is intact. However, despite the advantage of retention of vision clarity and usually uncomplicated post operative period, the procedure is complex, requiring high surgical skill, is expensive, is usually inaccurate, is relatively unsafe, with strong dependency on the surgeon's skill, and it can cause irregular astigmatism. These factors can be attributed to the viscous nature and relatively generally unsupported character of a cornea and the complexity of the microkeratome. In addition, it is an overly invasive surgical procedure, with all the attendant problems involved therewith.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and device to effect in situ internal corneal reshaping without the need for an ALK or similar surgical procedure;

It is a further object to utilize a high speed waterjet to effect controlled erosion of internal corneal tissue in si tu in a single step corrective procedure to minimize healing time and to provide healing, if necessary, with highest integrity.

It is yet another object of the present invention to effect the controlled erosion by means of the waterjet, in conjunction with a compression template which is configured to selectively compress portions of corneal tissue, which are to removed by erosion, with selected pressures.

It is still yet another object of the present invention to provide a method and device for the formation of an anchored flap which is anchored at two opposing sites whereby the flap cannot move from its proper position, and to effect the erosion removal beneath the anchored-in-place flap.

Generally the present invention comprises a method and device for the in si tu removal of internal corneal stroma tissue to effect a corneal reshaping for vision correction by means of a high speed waterjet. It has been discovered that a waterjet has different modes of cutting corneal tissue depending on the extent of compressive forces exerted on the tissue. Thus, light tensioned or minimally compressed corneal tissue is cleaved by a waterjet, i.e., layers of lamellae are cleanly separated without removal of any significant amounts of the corneal tissue. Increase of tissue compression (i.e., with the lamellae compressed together) above a threshold level relative to the waterjet speed and pressure, results in a resistance to the cleaving action and a controllable erosion (with tissue removal⁾ of the compressed tissue. The extent of erosion is roughly proportional to the amount of compression force applied to the corneal tissue.

In accordance with the present invention, the shape, size and position of corneal stroma tissue which needs to be removed for an appropriate correction, is determined. External pressure is then selectively applied to the anterior surface of the cornea, normal to the interior corneal stroma tissue to be removed and directly opposite thereto to thereby transmit compressive forces to the tissue to be removed. The extent of the external pressure applied is varied according to the amount of tissue to be removed.

While the cornea is in the selectively compressed state, a waterjet is laterally applied to the cornea, at a position in line with the corneal stromal tissue (just below the Bowman's membrane) . The waterjet is then scanned across the cornea in one direction or the other. Scanning is not edge to edge but incomplete to leave two anchoring sections at the peripheral lateral edges of the cornea to prevent displacement of the flap relative to the stromal bed.

In a single step, compressed tissue is removed by erosion (and washed away by the waterjet) with the remaining boundary tissue, on a line planar therewith (except for the hinge or anchoring sections), being only cleaved (i.e., minimally separated) but not removed. Remaining corneal tissue will fill in the void left by the removed tissue (usually done simply by smoothing and compressing the flap-repositioning of the flap is unnecessary because of the double, opposing anchoring) . Reshaping is complete. Since there is only a minimal removal of tissue without other tissue separation (cleaved layers are at most only minimally separated and keratocytes remain intact and in place) there is minimal trauma and healing is expected to be accelerated and of the highest integrity.

The present invention further comprises a method of forming an anchored lenticule, in the anterior corneal region or an eye comprising the steps of: a) perforating corneal stroma tissue adjacent to but spaced from a first side periphery of the cornea, with perforation means, to form a through-aperture parallel to a tangent at said side periphery; b) directing a waterjet, co-linear with the aperture, through the aperture, wherein the aperture is of sufficient diameter to permit the waterjet to pass therethrough without impingement of the waterjet with the walls of the aperture; c) laterally scanning the waterjet through the corneal stroma tissue to form a separation between stroma tissue; and d) stopping the separation of the stroma tissue at a point adjacent to but spaced from a second periphery of the cornea distal to the first periphery, such as by simply blocking the waterjet beam as it scans across the second anchoring position; whereby a lenticule with two anchoring elements is formed in the anterior portion of the corneal tissue. These and other objects, features and advantages of the present invention will become more evident from the following discussion and drawings in which:

SHORT DESCRIPTION OF THE DRAWINGS Figure 1 depicts an eye globe with a schematic showing of applied pressure and erosion area;

Figure 2 depicts the use of a flat compression template for use in applanation and myopic correction; Figure 3 depicts a cross section of a compression template with a circular ring or depression for correction of hyperopia;

Figure 3a is an expanded view <bf the apex of the globe 1 ' more clearly depicting the eroded volume; Figure 4 depicts use of a compression template in the form of a partial cylinder section for use in correction of astigmatism; and

Figures 5a and 5b are side and top schematic view respectively of the formation of a starter hole for the waterjet for use in providing the in situ erosion removal of corneal tissue with the tissue flap remaining in place and held by a double anchor.

DETAILED DESCRIPTION OF THE INVENTION The present invention is predicated on the unexpected discovery that a scanning waterjet cuts corneal tissue by cleaving or by erosion. Cleaving occurs when the tissue is under slight tension with a tension component perpendicular to the plane defined by the direction of waterjet scan and the direction of the waterjet beam. Erosion occurs when the tissue is under compression with a compression component perpendicular to the plane defined by the direction of scan and the direction of the beam. The degree of erosion is controlled by controlling the amount of compression. The degree and extent of local compression or tension can be controlled by a shaped template placed on the anterior surface of the cornea with or without suction. It is possible thereby to remove a shaped volume of tissue under the anterior surface of the cornea, interior to the stroma, while the cornea surface remains in place and is never removed. In order to maintain its position in place, the surface becomes a large diameter, double opposed anchor flap (a single hinge is also possible but should be more closely monitored to avoid movement of the flap) . After erosion removal of the compressed tissue, means such as gently stroking and smoothing of the cornea surface is used to cause existing stromal tissue to fill in the gaps caused by the erosion process. The tissues will adhere naturally just as does a soft contact lens to the anterior cornea surface. Since there is no removal of tissue other than by the erosion, healing time is minimal and healing is of high integrity.

The device of the present invention comprises a high speed waterjet source and preferably a shaped template adapted to contact (when placed and centered, or otherwise properly positioned on the anterior surface of the cornea) , portions of corneal tissue directly above the tissue to be eroded and removed (i.e., normal thereto) for the transmission of compressive forces thereto. The device further comprises means for controllably exerting compressive pressure on the corneal tissue via the template. In co-pending application serial no. 08/xxx,xxx a surgical trephine is used to cleanly peripherally score the anterior surface of the cornea to facilitate initial cleavage of the stromal tissue by providing direct contact access thereto by the waterjet. The trephine also facilitates the use of a vacuum template to maintain pressure on the corneal tissue .

The method of the present invention comprises the relatively simple steps of: a) compressing selected portions of corneal stroma tissue to be removed, (as determined to be required to effect a predetermined refractive vision correction) by compressing the anterior corneal surface normal to the selected portions; b) laterally directing a high speed waterjet at the compressed selected portions of stromal tissue; c) eroding and removing only the compressed selected portions of stromal tissue; and d) applying means to the cornea for filling in of removed stroma tissue with existing stroma tissue.

In effect, one can perform a procedure akin to keratomileusis in si tu in a single scan step, leaving a doubly anchored flap in place never moved from its normal position. The keratomileusis (lamellar keratoplasty) procedure is one involving lateral cuts of corneal tissue which initially involves surgical removal, with a microkeratome, of a uniform thickness button or lenticule of corneal tissue of a thickness containing the epithelium layer, Bowman's membrane (intact) and a portion of the stroma. The parallel lenticule usually is made to remain hingedly attached at one point to the cornea as a replaceable flap. The lenticule is folded back out of the way, the stroma bed is then surgically reshaped, with a knife blade or laser, as required, and the lenticule is replaced.

Though the waterjet is directed into the corneal tissue, there is no hydration or aeration of the corneal tissue since the beam passes completely through the tissue with minimal scattering. The cutting or eroding action is effected only by the leading edge side of the beam as it scans. This does not involve penetration of the tissue and hence there is no hydration. A myopic correction has been effected simply by pressing on the apex of the cornea with a flat template while cutting at normal IOP (intra ocular pressure) . However, hyperopic and astigmatic corrections are also possible in accordance with the following discussion and drawings.

An important safety characteristic of the present invention is that tissue erosion and removal cannot be effected without compression pressure which is only mechanically effected by a specifically preformed template. As a result, discretionary tissue removal, of even an accidental type, is minimized or altogether eliminated. The formation of a double anchored lenticule of corneal tissue is provided, as described, by the lateral scanning of a waterjet within the stromal tissue but spaced from the lateral edges. While termination of the scanning waterjet to provide a residual anchor element at the end of the scan is generally without complications, initial internal cutting may be problematic, with initial forward rather than lateral cutting. This would produce hydration and aeration. Accordingly the initial cut through the corneal tissue is preferably effected by through-hole starter means to provide a through hole in the corneal tissue into which the waterjet beam is directed. The starter hole is positioned to be laterally in line with the proposed scanning path of the waterjet and of sufficient dimension to permit the waterjet to pass therethrough without hydration of adjacent corneal tissue and whereby the waterjet is able to laterally engage the stromal tissue for the cleaving/eroding process of the present invention. In addition, to application for an internal cleaving and eroding, the formation of a double anchored lenticule results in formation of an in situ accessible pocket in the corneal tissue for insertion of opthomological devices such as an intrastromal lens.

In such embodiment the device further comprises means for selectively blocking access of the waterjet to selected portions of the corneal tissue, whereby the selected portions form the double anchors for the lenticule.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PREFERRED EMBODIMENT

Figure 1 shows the cutting conditions in a globe 1 (representing an eye with the corneal region 2, at the upper side thereof), for a refractive correction procedure, in accordance with the present invention. The vertical arrows show the azimuthally symmetric distribution of compressive/tensive forces on the anterior surface 2a for correction of myopia (for clarity, a compression template is not shown in this Figure but is shown as element 3 in Figure 2) . The shaded, internal volume 4 is the site of tissue removed by erosion. Otherwise, outside this volume, the tissue is, at most, cleaved by separation of layers but with no tissue loss or removal. The site of the eroded tissue is within the stroma 5, just below the Bowman's membrane layer 6. The dotted line d shows the lateral cutting trajectory for the waterjet passing through the tissue with only cleavage. As shown, the waterjet direction is perpendicular to the drawing, with the waterjet being laterally scanned. The double anchor 7a and 7b results from turning the waterjet off at the beginning and end of the trajectory (actually effected by blocking the beam as it scans at the desired end anchor regions) . It is however desirable though not essential to have a double anchor and a single hinge will do in keeping the flap in place. However, the double anchor ensures that the flap will remain in place and requires no adjustment. The waterjet carries away any tissue debris which is eroded so that no debris remains between the stromal bed and flap. As shown in Figure 2, for myopic corrections, the pressure template is flat, with compression pressure (shown by the dotted arrows) , being maximally exerted at the apex (the tangential point of contact) of the globe. Accordingly, erosion volume 4 is ovate, i.e., greatest at the center and tapering outwardly, whereby gap filling of volume 4 causes anterior surface 2a to flatten.

After the erosion procedure is effected, with removal of tissue as shown, a combination of the lateral tension in the flap, external air pressure and coaxing by the surgeon ensures that the flap or lenticule 20 (the corneal tissue above line d) collapses onto the stromal bed defined as the base of volume 4, whereby original corneal tissue fills in the gap, leaving a flattened anterior surface 2a. The proximity of the two interfaces will expedite healing.

Correction for hyperopia, is shown in Figure 3, wherein the azimuthally symmetric distribution of compressive/tensive forces puts the compression forces on a circular ring template 13 near the outer periphery of the cut near the anchors (as depicted by the dotted arrows) and tensive forces near the apex 12. Under such conditions, the eroded volume 14 is in the form of a ring, which steepens the curvature of the anterior surface 2a when the flap 20' collapses onto the stromal bed.

To correct for regular astigmatism, as shown in Figure 4, the compressive forces alternate azimuthally with two compressive maxima and two tensive maxima.

Various other forms of templates are possible but the most simple are usually the best with minimization of complications. Although vacuum templates are probably unnecessary, in each instance, the template is preferably comprised of a porous material and therefore able to create a low pressure region at its surface. Thus, wherever the template presses on the corneal tissue, it produces a compressive force and wherever it is on the corneal surface but not in firm contact it produces a tensive force. Porosity can also be utilized to control template weight and compression pressure if desired.

Figure 2, which illustrates that a template used for correction of myopia is merely a flat template 3, oriented parallel to the scan plane (basically shown by dotted line d) , that applanates the cornea near its apex. The force required to applanate a circular zone of a few millimeters in diameter is about 1 gram. The increase in IOP (internal optical pressure) with such compression pressure is small, and on the order of about 10%. The extent of applanation, i.e., the diameter of the applanation zone determines the degree of flattening or the amount of correction. Templates with a spherical shape may also be useful .

Figure 3 which illustrates a template suitable for correction of hyperopia comprises a circular ring (or alternately viewed as a circular depression in the center of the plate) which has a rectangular cross-section as shown, or a rounded corner 15. Compression occurs in a circular ring 14 and the eroded zone is in the form of a circle. This causes steepening of the anterior surface 2a when existing tissue fills in the circular volume ring 14 (shown in Figure 3a) . The extent of the applanation determines the degree of steepening.

Figure 4 which illustrates a correction for astigmatism utilizes a template which has a shape corresponding to that of a circular cylinder, a rod. In this case, the applanation zone is elliptical parallel to an element of the cylinder. The erosion zone corresponds to the applanation zone, flattening the cornea more along a meridian parallel to the axis of the cylinder than along a perpendicular meridian. The degree of applanation or the diameter of the applanation cylinder is used to control the extent of the correction.

Under some waterjet scan conditions the erosion is accompanied by some degree of rippling (striation) of the scanned surface. The direction of the striation marks is parallel to the direction of the waterjet beam. Accordingly, scan conditions should be chosen that will minimize striations. These conditions include the typical variables of waterjet beam diameter, beam speed and scan speed. In particular, vibration must be avoided. Experiments confirming the erosion operations depicted in the drawings were done with waterjets having a beam diameter of 33 m, a stagnation pressure of 20,000 psi (beam speed of about 450 m/s) and a scan speed of 10 mm/s.

Figures 5a and 5b illustrate, in detail the procedure for effecting a double anchored lenticule. A half cylinder needle 30 (of diameter sufficiently larger than that of the waterjet beam to permit the waterjet beam to pass therethrough) is inserted through the corneal stroma 5 at the peripheral edge of the area d to be cleaved/eroded. The perforation insertion is shown as being in a direction co-linear with the direction of waterjet beam 100. Accordingly, a through aperture 31 is formed through which the stationary waterjet beam 100 passes without engaging and aerating the walls thereof. To insure co-linearity of the beam with the perforation aperture, the needle 30 is positioned on the same block from which the waterjet emanates. Once the waterjet 100 is initially freely directed through aperture 31 it is scanned in the direction of the arrow to the opposite side of the globe, while following path d where it effects the laterally directed cleavage/erosion, as describe above, without hydration. In order to ensure that the waterjet beam does not impinge on the cornea except along line d but not beyond the peripheral ends thereof (i.e. to provide intact anchoring sections 7a and 7b) beam blocker elements 40a and 40b (shown in Figure 5b) are positioned between the waterjet source and the area defined by section 7a and 7b respectively, whereby the waterjet beam is prevented from reaching the cornea in such areas. As a result, these areas remain intact as the anchoring regions for the formed lenticule or flap 20. The through-aperture 31 is positioned tangential to the first blocker element 40a, whereby the waterjet beam 100 passes the first blocker element 40a and immediately enters aperture 31 as the initialization of the corneal tissue scanning cleavage/erosion, described above. The first blocker element 40a is not however necessary if the waterjet beam is stationary within the through-aperture 31 when the scan is started.

It is understood that the above discussion and drawings are illustrative of the present invention and that details contained therein are not to be construed as limitations on the present invention. Changes may be made in applicable steps and conditions without departing from the scope of the present invention as defined in the following claims.

Claims

What is claimed is:

1. A method for effecting refractory vision correction by corneal tissue reshaping comprising the steps of: a) compressing selected portions of corneal stroma tissue to be removed, by compressing the anterior corneal surface normal to the selected portions; b) laterally directing a high speed waterjet and scanning across the compressed selected portions of stromal tissue; c) eroding and removing only the compressed selected portions of stromal tissue; and d) applying means to the cornea for filling in of removed stroma tissue with existing corneal tissue.

2. A method of forming an anchored lenticule, in the anterior corneal region or an eye comprising the steps of: a) perforating corneal stroma tissue adjacent to but spaced from a first side periphery of the cornea, with perforation means, to form a through-aperture parallel to a tangent at said side periphery; b) directing a waterjet, co-linear with the aperture, through the aperture, wherein the aperture is of sufficient diameter to permit the waterjet to pass therethrough without impingement of the waterjet with the walls of the aperture; c) laterally scanning the waterjet through the corneal stroma tissue to form a separation between stroma tissue; and d) stopping the separation of the stroma tissue at a point adjacent to but spaced from a second periphery of the cornea distal to the first periphery; whereby a lenticule with two anchoring elements is formed in the anterior portion of the corneal tissue.

3. The method of claim 2, wherein said method is used in effecting refractory vision correction by interior corneal tissue reshaping beneath the lenticule, comprising the steps of: a) compressing selected portions of corneal stroma tissue to be removed, by compressing the anterior corneal surface normal to the selected portions whereby said scanning of the waterjet across the compressed selected portions of stromal tissue causes said separation of stromal tissue to be effected by cleavage and erosion of the stromal tissue, with the erosion, with removal of stromal tissue, being only of the compressed selected portions of stromal tissue; and b) applying means to the cornea for filling in of removed stroma tissue with existing corneal tissue.

4. The method of claim 3, wherein the internal erosion and removal of stromal tissue is shaped by the compressing and erosion of selected portions thereof to provide a correction for myopia .

5. The method of claim 3, wherein the internal erosion and removal of stromal tissue is shaped by the compressing and erosion of selected portions thereof to provide a correction for hyperopia .

6. The method of claim 3, wherein the internal erosion and removal of stromal tissue is shaped by the compressing and erosion of selected portions thereof to provide a correction for astigmatism.

7. A device for effecting the method of claim 1, comprising a high speed waterjet source and a shaped template adapted to contact, when properly positioned on the anterior surface of the cornea, portions of corneal tissue normal to the tissue to be eroded and removed, for the transmission of compressive forces thereto, and means for controllably exerting predetermined variable compressive pressure on the corneal tissue via the template.

8. A device for effecting the method of claim 3, comprising a high speed waterjet source and a shaped template adapted to contact, when properly positioned on the anterior surface of the cornea, portions of corneal tissue normal to the tissue to be eroded and removed, for the transmission of compressive forces thereto, and means for controllably exerting predetermined variable compressive pressure on the corneal tissue via the template, said device further comprising means for selectively blocking access of the waterjet to selected portions of the corneal tissue, whereby the selected portions remain as anchoring elements for the separated tissue, and means for perforating the corneal tissue with a through-aperture through which the waterjet is directed for subsequent lateral engagement of the waterjet with the corneal tissue to effect the cleavage and erosion with removal of corneal tissue.

9. The device of claim 8, wherein the shaped template comprises a flat shape for effecting removal of corneal tissue for correction of myopia.

10. The device of claim 8, wherein the shaped template comprises a circular ring wherein said compression occurs in a circular ring and the erosion of tissue is in the form of a circle for correction of hyperopia.

11. The device of claim 8, wherein the shaped template comprises a shape corresponding to that of a circular cylinder, wherein an applanation zone between the template and cornea is elliptical, parallel to an element of the cylinder and wherein erosion of tissue corresponds to the applanation zone, flattening the cornea more along a meridian parallel to the axis of the cylinder than along a perpendicular meridian, with the diameter of the applanation cylinder adapted to be used to control the extent of a correction for astigmatism.

12. The device of claim 8, wherein the perforation means comprises a half cylinder needle having a diameter grater than that of the waterjet.