Keratoprosthetics

In cases where corneal transplantation cannot provide transparent engraftment, keratoprosthesis is performed - replacement of the cloudy cornea with a biologically inert plastic material. There are 2 types of keratoprostheses - non-penetrating, used for bullous edematous cornea, and penetrating, used for burn leukomas. These keratoprostheses have different designs.

Penetrating keratoprostheses are intended for the treatment of coarse vascularized burn leukomas when both eyes are affected, when the retinal function is preserved, but there is no hope for transparent engraftment of the corneal transplant. The operation is performed in two stages. First, the leukoma is stratified into two plates and the supporting metal part of the prosthesis, curved according to the curvature of the cornea, is placed in the formed pocket. The supporting plate has 2 large openings at the edges. Within these openings, the stratified cornea grows together and fixes the keratoprosthesis. In the center of the supporting plastic, there is a round opening for placing the optical part of the prosthesis. At the first stage of the operation, it is closed with a temporary insert (plug).

The second stage of the operation is performed after 2-3 months. By this time, the support plate of the prosthesis is already firmly fixed in the layers of the leukoma. A trepanation of the cloudy layers of the cornea with a diameter of 2.5 mm is performed above the central opening of the keratoprosthesis. The temporary plug is unscrewed with a special key. The inner layers of the cornea are excised and an optical cylinder is screwed in place of the temporary insert. The optical power of the keratoprosthesis is calculated individually for each eye. On average, it is 40.0 D. If the operated eye does not have a crystalline lens, the keratoprosthesis compensates for the entire optical power of the eye, i.e. 60.0 D. The inner and outer parts of the optical cylinder protrude above the surfaces of the cornea, which prevents it from overgrowing.

After the operation, patients should be under the supervision of a doctor, as they may develop complications. The overgrowth of the optic cylinder on the anterior or posterior surface is removed surgically. The optic cylinder can be replaced in case of optics mismatch or insufficient protrusion above the anterior or posterior surface. When using a two-stage surgical technique, filtration of the anterior chamber fluid is rarely observed. The most frequent and alarming complication is the exposure of the supporting parts of the keratoprosthesis due to aseptic necrosis of the superficial layers of the cornea. To strengthen the prosthesis, donor cornea and sclera, autologous cartilage of the auricle, mucous membrane of the lip and other tissues are used. In order to avoid these complications, keratoprosthesis models and surgical techniques continue to be improved.

Non-penetrating keratoplasty is performed for bullous corneal dystrophy. The operation involves inserting a transparent plate with holes along the periphery into the corneal layers. It covers the anterior corneal layers from excessive moisture saturation of the anterior chamber. As a result of the operation, the overall swelling of the cornea and the bullous epithelium are reduced, which in turn relieves the patient from pain. However, it should be noted that the operation only slightly improves visual acuity and only for a short period of time - up to 1-2 years. The posterior corneal layers remain edematous, and the anterior ones gradually thicken and become cloudy. In this regard, at present, thanks to the improvement of the technique of penetrating subtotal keratoplasty for edematous corneal dystrophy, corneal transplantation is preferable.

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