Method of and surigical operation for operating cornea in order to cause refractive correction of vision

The subject of the invention is a surgical device for refractive correction of vision, especially for corneal eye surgery.

Many surgical procedures are known to change the shape of the cornea for refractive correction of vision, some recently developed. One of the well-known surgical procedures (radial keratotomy - RK - radial incision of the cornea) involves radial incision of the cornea to flatten the shape of the anterior surface of the cornea and thus correct myopia. The condition for effective and safe implementation of this surgical procedure are high skills and proper assessment of the situation. In addition, correcting myopia by flattening is usually not permanent, even if properly performed, and over time leads to the gradual development of hyperopia.

Other recently developed surgical procedures involve removing selected parts of the front surface of the cornea (i.e. corneal tissue) with the intention of changing the effective curvature of the cornea by changing the focus of the image. Corneal curvature change is used to provide appropriate refractive vision correction.

In a relatively recently developed device with an excimer laser, photochemical separation is used instead of physical cutting. Corneal tissue is gradually removed through subsequent stages using a series of laser pulses. This method, known as photorefractive keratotomy (PRK), is basically safe and effective. However, PRK surgery has some shortcomings, not including very expensive equipment. The most important of these is the error rate, or lack of correct refraction, of the order

180 197 ± 0.5 diopters, compared with an error of ± 0.25, typical when using glasses or contact lenses. In addition, the effect of using the laser is a rough corneal surface. In addition, the cornea has long-lasting physiological effects associated with its interaction with the laser during separation, which may be the cause of gradual reversal of correction or complications associated with treatment and the possibility of mutagenic effects.

The cornea contains a thin epithelial layer covering the upper part of the Bowman layer or membrane, which in turn covers the main corneal stroma. The epithelium regenerates, whereas Bowman's membrane does not. During ablative corneal tissue removal procedures, such as the PRK method, epithelium and Bowman's membrane are removed, including part of the stroma. The epithelium is then regenerated on the exposed outer surface of the cornea except directly on the stroma, because Bowman's membrane does not regenerate. However, direct reconstruction of the epithelium on the stroma can cause undesirable corneal haze, which gradually disappears over time. PRK is not yet authorized for use in the USA.

Due to innate instabilities and error rates, both RK and PRK are usually not suitable for correcting myopia above -6 diopters, and PRK is currently not suitable for correcting other defects except myopia. The operation called Automated Layered Keratoplasty (ALK) does not damage the Bowman membrane and is used to correct defects up to -20 diopters. This procedure involves the initial removal using a microceratotome of the disc or lens of corneal tissue of uniform thickness along with the epithelial layer, Bowman's membrane (undamaged) and part of the stroma. Preferably, the disc or lens remains hinged to the cornea at one point. Then the lens is moved aside, and then, if necessary, surgically changes the shape of the stroma bed, puts the lens back on ensuring proper adhesion and healing of the stroma-stroma surface and preserves the Bowman's membrane without damaging the cornea. It turns out that the healing of the stromal-stromal syndrome after the ALK procedure reduces, if not eliminates, the healing instability, making this procedure most suitable for large refractive corrections.

However, despite the advantage of maintaining visual clarity and stability of healing, it is not recommended to use this procedure due to its complexity, requiring high surgical skills, costliness, usually inaccuracy, strongly dependent on the surgeon's skill, as well as the possibility of causing irregular astigmatism. These factors can be attributed to the sticky consistency and relatively loose structure of the cornea, as well as the reflex movements of the eyeball, which makes it difficult to use a scalpel, or even a microkeratotome and is associated with large inaccuracies.

The object of the invention is to obtain a surgical device for refractive correction of vision, especially for corneal eye surgery.

The surgical device for refractive correction of vision, especially for operating the cornea of ​​the eye, comprising a mold placed and centered on the front of the corneal tissue to be removed, according to the invention is characterized in that the mold has a non-flat surface adapted to the front of the removed corneal tissue, deforming it, the anterior part of the corneal tissue is limited by the anterior and posterior surfaces of the mold, and the height of the non-flat surface of the mold relative to the plane at the end of the mold is equal to the difference in height between the anterior and posterior surfaces of the removed corneal tissue, and on the outside of the mold there is a ring attached to it by means of locking paws, to which the suction assembly and the corneal cutting assembly are connected mikrokeratotomu.

Preferably, the micro-keratotome comprises a water nozzle connected to a water inlet with a high outlet velocity produced by means of a pressure between 20,700 kPa and 138,000 kPa and a water outlet.

Preferably, the microkeratotome cutting blade is a water jet in the form of a flat cutting surface.

Preferably, the water nozzle is positioned relative to the flat surface of the removed part of the cornea by a water guide.

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Preferably, the mold is porous.

Alternatively, the ring includes a groove to move the hinged lens away from where it would interfere with the placement of the mold on the cornea.

Thanks to the solution according to the invention, a device for refractive vision correction has been obtained, characterized by the advantages of ALK type procedures, but with greater accuracy and less complexity. In addition, a device was obtained with an accuracy at least comparable to that obtained with the use of glasses or contact lenses, maintaining, in principle, smoothness, gloss and transparency of the original corneal tissue.

The object of the invention is illustrated in an embodiment in a drawing in which: Figure 1 is a cross-sectional view of the eye with a portion of the cornea marked for removal; Fig. 2 is a hinged outer corneal lens; Fig. 3 placing the mold according to the invention on a removable cornea; Figures 3a, 3b and 3c - forms for correcting myopia, hyperopia and astigmatism, respectively, in cross sections; and fig. 4 and 4a - the use of a water nozzle and a guiding cutting ring for the mold and the corneal tissue to be removed, in cross-section and plan view, respectively.

The present invention generally relates to a device for the selective, accurate cutting of corneal tissue and changing its curvature for refractive correction of eye vision.

Figure 1 shows the human eye in cross section, schematically. It has been calculated that for proper refractive vision correction, the corneal part 11 should be removed with a dashed line 10. However, the base 11a of the part 11 to be removed is curvilinear, which makes it difficult to check the accuracy of its removal. Part 11 consists of part of the epithelium 12 and the Bowman layer 13, as well as a fragment of the stroma 14 of the cornea 10.

Figure 2 shows the ALK procedure consisting in hinging the lens fragment 15, epithelium 12, Bowman layer 13 and corneal stroma 10 from their place. The drawing also shows the cornea 10 with the portion 11 'to be removed for refractive vision correction. In this example, part 11 'consists only of the corneal stroma 14 fragment 10, wherein the base 11a of part 11' is still curvilinear.

According to the invention, as can be seen in Figure 3, a mold 20 is applied to part 11, or more preferably, to part 11 ', which deforms the part on which it is deposited, as a result of which the surface of the base 11a acquires a flat shape, suitable for for flat cutting as shown in fig. 4. As seen in cross sections, respectively in fig. 3a-3c, forms used to correct myopia with increased curvature 20a are shown; correcting hyperopia with increased curvature of the 20b optical zone; and correcting astigmatism with a steep curvature along the horizontal meridian 20c - in horizontal and vertical cross-sections. In each of these embodiments, the appropriate form is adapted to the type of correction (myopia, hyperopia and astigmatism) and to the necessary degree of correction. After matching, the respective molds 20a-c result in a suitable deformation of the parts to be removed so that at the base of the mold, as seen in Figure 3, an outwardly exposed flat cutting surface is formed.

Figures 4 and 4a show a mold 20 positioned on the cornea 10. A water jet cutting guide 30 is positioned in relative position thereto in such a way that the flat base 11a of the removed portion 11 is exposed and in tune with the water jet nozzle 31. The water guide 30 is in the form of a ring 32 in which there is a water outlet 34. The mold 20 is placed concentrically inside the ring 32 and locked in this position by means of the locking tabs 25 and 26. In order to ensure that the deformation effectively converts the flat surface into the actual cutting surface (i.e. that after cutting off the cornea loosens to the correct shape), a vacuum is applied through the porous mold 20 that closely matches the surface 11b of the cornea 10 with the inner surface 20 'of the mold 20. This vacuum should be maintained at least until the flat surface 11a is cut off. The water nozzle 31 is rectilinear (in the form of a thin gap) with a width e.g. 6 mm, suitable for ejecting water in the form of a cutting plane at least equal to the width of the flat base 11a. As a result, a single pulse of water or a series of pulses accurately cuts off the cornea within very much

180 197 short time in the required manner without having to move the nozzle 31 relative to the cornea 10.

Due to the flat cutting with positioned, adjustable elements and thanks to the full support of the cornea during cutting, the accuracy of the procedure is very high. In addition, there are no heating or abrasive elements in the water stream. The flat cut surface maintains the smoothness and gloss of the original corneal tissue 10.

After cutting, the mold 20 and ring 32 are removed from the cornea. If the cut is performed without the use of ALK, the corneal correction is complete.

If, on the other hand, the ALK procedure is used (as can be seen in Fig. 4a), then in the ring 32 there is a groove 34A for hinging the lens 15 and removing it from the cutting blade 40. Then the hinged epithelium is placed on the cut tissue of the stroma for healing mornings according to a known procedure

The method of removing corneal tissue by means of the device according to the invention consists in determining the dimensions, shape and position of the anterior part of the corneal tissue which must be removed in order to obtain adequate refractive vision correction; a surface, usually curvilinear, is then determined along which corneal tissue must be dissected to remove anterior corneal tissue and to achieve adequate refractive correction; the front part of the corneal tissue is deformed with the help of deforming means, as a result of which the cut surface takes a flat shape; then cut along a flat surface with a cutting tool.

As mentioned above, the anterior portion to be removed may also contain corneal stroma tissue that is removed below the lens or disc, as in ALK procedures.

The device according to the invention comprises a deforming element in the form of a non-planar molding element. This mold is specially adapted to be placed and centered in the anterior part of the removed corneal tissue so that it includes a non-flat surface to which the removed anterior part adapts, which causes it to deform.

This deformation is for the most part controlled so that the surface to be cut, which is at the base of this front part, assumes a flat shape that is accessible and thus a cut can be made. The height of the non-flat surface of the mold from the plane of the base of the mold is equal to the calculated difference, point by point, the difference in height between the fore and aft of the part of the corneal tissue to be resected. The calculated difference must also take into account geometric deformation and tissue contraction. As a result, the back surface (i.e. the surface to be cut) assumes a flat shape. It should be noted that there should be taken into account (with some fluctuations in the shape of the form) the existence of some distortion of the transverse spacing when flattening the posterior surface without significant corneal compression.

When initially determining the dimensions, shape and position of the anterior part of the corneal tissue (which needs to be removed for proper refractive correction of vision), the foreseeable effect of epithelial reconstruction and wound healing on the changed shape should be considered.

A number or set of non-flat forms, differing in shape and dimensions, are used for various refractive corrections, although forms that are specifically tailored to a particular case can be easily constructed if desired. Molds, including custom-made molds, can be made in a variety of ways, for example, from porous metal, such as sintered stainless steel, from which products can be appropriately formed during highly accurate electrospark machining processes.

The metal porosity is an advantage in that it is advantageous that the non-flat area in which the front cornea fits, also acts as a "vacuum handle" holding the removed part of the cornea, which ensures tight fitting and pressure during the cutting step. Preferably, it is recommended to use vacuum holding means with a sufficient minimum transverse holding force. porous walls of the mold, e.g.). through the pores inside it, micrometer in diameter, made of materials such as sintered stainless steel. This is to better fit and hold the front part pressed against its non-flat surface.

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The shape of the mold for a given specific correction depends on the relative position of the cutting plane and these parts must be well stabilized. The molds can be made of sintered stainless steel with a high porosity exceeding 24% so that suction can occur. You can also use thin-walled glass tubes with a very small diameter, in a circular arrangement, the ends of which are positioned so that they shape the shape of the mold. Typical mold dimensions are a diameter of 6 mm with surface deviations from flatness of 150 microns or less. Another solution is to use a cavity system in the form of elements connected to a vacuum.

Most preferably, the cutting agent is a rectilinear stream of water (sterile saline) formed at a high velocity outlet jet produced at a pressure of 20,700 kPa to about 138,000 kPa, preferably 41400 kPa to about 55,200 kPa. The higher the pressure, the faster the water leaving the nozzle. It has been shown that this type of water jet from a small diameter nozzle provides a very smooth transverse cut through the corneal tissue with a smoothness and gloss similar to the original tissue surface.

In order to further increase the accuracy of the method and apparatus of the invention, it is recommended to eject the water with a cross-section stream in the form of a flat cutting layer, which can provide a cross-cut without moving the water stream relative to the tissue, although the moving cutting stream is within the scope of the invention. Appropriate dimensions of a flat aqueous cutting stream are about 6 mm per 25 microns. In this type of embodiment, the water stream can be controlled by means of an annular element with a corresponding slot cut out in it on part of the circumference. The annular element is mounted around the mold on the cornea and positioned in such a way that the dosing gap is laterally synchronized with the flat cutting surface. After proper placement of the mold, the impulse-started stream of water crosses the corneal tissue held in the mold transversely within a fraction of a second, leaving the surface smooth. In addition, the ring includes an auxiliary opening opposite the slot and intended to receive and discharge the ejected water stream.

In a preferred embodiment of the device according to the invention, the water-jet microkeratotom has two main parts: a cutting ring and a water-jet forming element and its handle. This type of microkeratotoma is used as described below. The vertical meridian and the center of the axis of vision are determined with a device similar to the one used in the RK method and marked with a standard tool also used in the RK method. The cornea is viewed through a working microscope. The cutting ring is placed on the cornea, after which it is centered and properly moved relative to the marks on it. A suction source is connected to the cutting ring, thanks to which it adheres strongly to the cornea. Then the mold with the handle is placed in the center of the cutting ring and locked in this position. This solution ensures appropriate repeatable unambiguous location of the mold relative to the cutting plane and the possibility of cutting relative to the mold.

It goes without saying that the detailed solutions shown in the drawings and described are only intended to illustrate the present invention and that it is possible to change both the method of performing the procedure and the device for its implementation without departing from the scope of the invention as defined in the following claims.

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