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Keratoconus is the most common degenerative change which occurs in the cornea, characterized by non-inflammatory progressive thinning of the cornea, which acquires a conical shape. It affects about one person in two thousand inhabitants, and it’s more often encountered in men than in women. It occurs in all populations around the world, although it occurs more frequently in certain ethnic groups.
The exact cause of keratoconus is still unknown, but is thought to be associated with poor enzyme activity within the cornea. A genetic predisposition has aslo been established. The progression of keratoconus is rapid in patients with Down syndrome. It is believed that the disease usually affects both eyes, but usually one eye has a more pronounced disease progression. Usually the most progress is seen in adolescence and then it stabilizes (though this is not a rule).
The most common occurrence is the unilateral decline in visual acuity due to progressive myopia and astigmatism, which becomes irregular. The main symptoms are: central and paracentral thinning of the corneal stroma (which acquired a conical shape).
Treatment of mild to moderate keratoconus is wearing of spectacles and semi-hard or hard contact lenses and regular monitoring of disease progression. For progressive forms of the disease patients are advised to undertake the crosslinking method. Patients who tolerate lenses are often satisfied with their vision. Patients with advanced stages of keratoconus, those patients who can not wear lenses or their visual acuity declines to below 30%, and patients with significant thinning of the cornea are candidates for corneal transplantation. If there is a corneal decompensation and cornea has irretrievably lost its transparency, than perforative corneal transplantation is the only method to treat these patients. The best techniques that are used for diagnostics and monitoring of the course of the disease are OCT-optical coherence tomography of the front part of the eye and Pentacam- computerized corneal topography.
Crosslinking is a relatively new method which began being used some twenty years ago. The primary goal of the method is to slow down the progression of keratoconus, but other corneal ectasia as well. Crosslinking is also said to be a treatment which “buys time,” that is it maximally tries to prolong the period of development until a corneal transplant is eventually needed. This is achieved by strengthening the cornea and increasing the number of “anchors” that bond collagen fibers together. The main factors in cross-linking are riboflavin (vitamin-B2) and ultraviolet A light treatment (UV-A), which form a type of “cement” which then slows down the progression of keratoconus.
The developer of this method is Dr. Theo Seiler, from the Institute for Refractive Surgery IROC in Zurich. Our doctors at Svjetlost Clinic perform this procedure exactly by the strict protocols defined by IROC.
Patients with keratoconus seeking crosslinking treatment must satisfy the following criteria:
1. Corneal thickness must be at least 400 microns
2. The steep corneal meridian should not have a curvature which exceeds 58 diopters
3. The cornea must be transparent, without scars
4. Maximal visual acuity with eyeglasses must be less than 0.9
5. Earlier corneal ailments must be taken into account
6. The procedure is not advised for pregnant women because of possible changes in the cornea during this time
The eyes are locally anesthetized using anesthetic eye drops. The epithelial layer of the cornea is removed using a fine spatula, which is completely painless to the patient. Deepithelialization enables riboflavin to deeply enter through all corneal layers into the anterior chamber, thus better protecting the cornea itself and the deeper parts of the eye. Riboflavin is administered for 20 to 30 minutes, every two to three minutes. The ready cornea is then exposed to UV light for 30 minutes using a crosslinking lamp. Corneal thickness is constantly measured during this time. During the UV light phase of the procedure, riboflavin is administered every 5 minutes. The last step requires applying a soft contact lens on the cornea, which is removed after complete corneal epithelialization (3-5 days). During the postoperative phase of treatment, local eye drops are applied regularly. Patients will feel pain in the eye after the treatment, of which they are of course informed beforehand.
Most patients wear RGP lenses before crosslinking treatment. During the next few weeks after the operation the lenses are not worn. After that, the patient can try them on again, but has to take under consideration that they might not be adequate because corneal parameters can change; especially during the first 6 to 12 months after the operation, when curvature may be milder. In this case, new RGP contacts might be necessary.