The Role of Anterior Segment Optical Coherence Tomography in Evaluation of the Keratoconic Cornea After Corneal Collagen Cross Linking.

Keratoconus is a bilateral, asymmetric, progressive, non-inflammatory corneal ectatic disorder that is characterized by progressive thinning, steepening and potential scaring. Usually it affects the inferior or central cornea that becomes thinner and bulges forward in a cone-shaped fashion, inducing irregular astigmatism and myopia and reducing the quality of vision. Approximately 50% of clinically normal fellow eyes will progress to KC within 16 years. The greatest risk is during the first 6 years of the onset.

Annual incidence of KC also varies greatly from 0.002% , to 0.23% of 100,000 population per year. Most of the western studies support the lower figure of 0.002% , while in the Middle-East it is about 0.02 per year. In the middle-East, there is about ten-fold higher incidence (0.02% compared to 0.002%), and ten-fold higher prevalence (2.34% compared to 0.23%), as compared to Western counries.

Management of keratoconus depends on a variety of factors including visual acuity, the degree of corneal thinning and steepening. Rigid gas permeable contact lenses (RGPs) have been tried to correct corneal irregularity and astigmatism in keratoconus but they don't stop keratoconus progression. Corneal collagen cross linking (CXL) is now considered as the treatment of choice in mild to moderate cases of keratoconus and is proven to halt the disease progression. The implantation of intrastromal corneal ring segments (e.g. INTACS, Ferrara & Keraring) has been indicated for cases with moderate keratoconus to flatten the steep irregular corneas. Advanced cases of keratoconus with marked deterioration of vision or corneal scarring may be good candidates for deep anterior lamellar or penetrating Keratoplasty (DALK or PKP).

Collagen cross-linking (CXL) is a relatively new conservative approach for progressive corneal ectasia, which is able to strengthen corneal tissue reforming new covalent bonds. This strategy is based on the underlying pathology of the disease. Corneal collagen cross linking (CXL) idea was based on the fact that a photosensitizer substance like riboflavin (vitamin B2) can interact with ultraviolet irradiation (Ultraviolet-A) to strengthen the corneal tissue inter and intrafibrillar collagen bonds thus preventing further thinning, corneal protrusion and reduces corneal irregular astigmatism.

Epithelial debridement enhances riboflavin corneal penetration that allows absorption of wide range of light spectrum wave lengths including ultra violet A.