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In cases where corneal transplantation can not give a transparent engraftment, keratoprosthetics are produced - replacing the turbid cornea with a biologically inert plastic material. There are 2 types of keratoprostheses - non-blind, used with bullous edematous cornea, and through, used for burns. These keratoprostheses have a different design.
End-to-end keratoprostheses are designed to treat gross vascularized burns in both eyes when the function of the retina is preserved, but there is no hope of a transparent engraftment of the corneal transplant. The operation is performed in two stages. First, the thong is stratified into two plates and a supporting metal part of the prosthesis is bent into the formed pocket, curved according to the curvature of the cornea. The support plate has 2 large holes at the edges. Within these openings, the exfoliated cornea fuses and fixes the keratoprosthesis. In the center of the supporting plastic there is a circular hole for placing the optical part of the prosthesis. At the first stage of the operation it is closed by a temporary insert (blank).
The second stage of the operation is performed after 2-3 months. By this time, the base plate of the prosthesis was firmly entrenched in the layers of the belly. Above the central aperture of the keratoprosthesis, trepanation of turbid layers of the cornea with a diameter of 2.5 mm is performed. The temporary plug is unscrewed with a special key. The inner layers of the cornea are excised and the optical cylinder is screwed into place of the temporary liner. The optical strength of the keratoprosthesis is calculated individually for each eye. On average, it is equal to 40.0 diopters. If there is no lens in the operated eye, the keratoprosthesis compensates the entire optical power of the eye, ie, 60.0 diopters. The inner and outer parts of the optical cylinder protrude over the surfaces of the cornea, thus avoiding its overgrowing.
After the operation, patients should be under the supervision of a doctor, as they may experience complications. The growth of the optical cylinder on the front or back surface is surgically eliminated. The optical cylinder can be replaced in case of a mismatch between the optics or its insufficient stability above the front or rear surface. When using a two-step technique, the filtration of the anterior chamber moisture is rarely observed. The most frequent and disturbing complication is the exposure of the support parts of the keratoprosthesis due to aseptic necrosis of the surface layers of the cornea. To strengthen the prosthesis use the donor cornea and sclera, autochondria of the auricle, the mucous membrane of the lip and other tissues. In order to avoid these complications, they continue to improve the models of keratoprostheses and the technique of the operation.
Non-dermal keratoprosthetics are performed with corneal bullous dystrophy. The operation is that a transparent plate with holes around the periphery is inserted into the corneal layers. It covers the front layers of the cornea from excessive impregnation with the moisture of the anterior chamber. As a result of the surgery, the overall swelling of the cornea and bullous epithelium decrease, which in turn relieves the patient of the pain syndrome. However, it should be noted that the operation only slightly improves visual acuity and only for a short time - up to 1-2 years. The posterior layers of the cornea remain edematous, and the anterior layers gradually become denser and cloudy. In connection with this, at the present time, due to the improvement of the technique of percutaneous subtotal keratoplasty in edematous corneal dystrophy, corneal transplantation is preferable.