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Corneal Crosslinking

Probably one of the most exciting developments in corneal surgery the past decade, is the advent of UV-light induced corneal cross linking.  This novell procedure is the result of careful observation by innovator Theo Seiler from Switzerland during the early 1990s. He got the idea after visiting his dentist, and observed that the properties of UV light was utilized to strengthen the filling in his tooth.  He thought that if it was possible to apply this technology in dentistry, it should be possible to do the same in keratoconusKeratoconus is an eye condition that causes the cornea to spontaneously bulge outward, like the tip of a rugby ball. It causes very high levels of myopia and astigmatism. See Eye Diseases – Keratoconus., with a few modifications to the technique.

The corneal stromaThe cornea consists of 5 distinct layers. The third layer forms the main body of the cornea and is known as the corneal stroma. See Info on Eyes – Anatomy. consists, among other elements, of collagen fibres in geometric array.  These fibres form a lattice, and are maintained in their highly organized configuration by chemical bonds among themselves.  With ageing, under the influence of UV light from natural sources, these bonds tend to increase in number, thereby progressively reinforcing the corneal structure over time.  This is probably the reason why it is rare to find progressive keratoconus in elderly patients.

Corneal cross linking is aimed at increasing the cross-links through medical intervention between the collagen fibers of the corneaThe cornea is the clear, transparent 'front window' of the eye through which light enters the eye. It handles about two-thirds of the focusing power of the eye and is critical for good vision. See Info on Eyes – Anatomy., which reinforces the ectatic unstable cornea.  It is said that a cross linking procedure selectively ages the cornea by approximately 10 years.

The surgical procedure involves removal of the corneal epithelium, whereafter Riboflavin drops are applied every 3 minutes for 30 minutes until the cornea is saturated with the vitamin.  The rationale is to provide a UV blocking filter in the cornea itself, to prevent UV damage to the internal ocular structures.  Riboflavin has a yellow color, which captures the UV light frequency used in the procedure.  Calibrated UV radiation is then directed onto the cornea for between 5 and 30 minutes, depending upon the light source in use, while continuing to apply balanced salt solution every 3 minutes.  The Riboflavin also acts as a catalyst and oxygen rich free radicals are created that stimulates the linking between the corneal lamellae.

The procedure is done on one eye at a time.  The linking is only complete after 6 months to 2 years after the procedure, since the whole cascade of chemical linking is only triggered by the procedure.  One may therefore only assess the outcome after a period of 2 years.

This procedure is believed to stop progression and, in some cases, even lead to regression of keratoconus.