Keratoconus is a rare disease which causes the cornea to become increasingly thin over time. The thinning and the natural interior pressure of the eye cause the lower, and later the upper, layers of the cornea to bulge conically outward. The patient’s vision deteriorates with the increased bulging of the cornea.
Contact lenses with a stable shape can correct the defective vision for a long time. Only 20 percent of those affected require a cornea transplant as the keratoconus progresses.
The causes of keratoconus are not yet completely known. Scientists assume that the thinning of the cornea is triggered by a metabolic disease or is congenital.
Nor is there any general information as to the course of the disease. In most cases, the keratoconus develops from a pre-existing corneal irregularity, and the transitions are fluent. The patient suffers from frequent changes and decreases in visual acuity within months, weeks or days. The symptoms of keratoconus include such phenomena as double vision or additional shadows on letters of the alphabet and objects.
Up to now, the only treatment for keratoconus was a cornea transplant. A new therapy now allows photochemical stabilisation of the corneal tissue (see figure). With this so-called collagen cross-linking, the top layer of the cornea, the epithelium, is ablated and riboflavin (vitamin B2) is applied as a photosensitiser. The tissue is then subjected to UV-A light for about 30 minutes. This allows the generation of additional connections, so-called cross-linkings, between the individual collagen fibres of the cornea.
The fibres form a thick web, which results in an increase in the overall stability of the cornea. The results of the therapy are very positive: no progression of the keratoconus was observed in any of the patients that were treated. Currently studies are underway to discover whether refractive laser surgery on cross-linked keratoconus patients is possible at a later time.
