Oxygen free radical damage in the cornea after excimer laser therapy

Aims/background - To evaluate the extent of oxygen radical damage in the cornea after excimer laser ablation. Methods - The 193 nm argon fluoride excimer laser was programmed for an average fluence of 150 mJ/cm², with a firing rate of 5 Hz and an ablation zone diameter of 6 mm. Phototherapeutic keratectomy was performed to remove 30 μm of epithelium and 50 μm of stroma from the corneas of New Zealand white rabbits. Oxidative tissue damage after laser was determined by measuring oxidised lipids (conjugated dienes and ketodienes) in corneal lipid extracts, and by fast blue B staining to localise the lipid peroxide in the tissue. Results - Conjugated diene levels were 3.73 (SD 0.56) nmol per hemicornea in ablated corneas and 1.99 (0.33) nmol per hemicornea in normal corneas (p = 0.0044). Ketodiene levels were 2.72 (0.38) nmol per hemicornea in treated corneas and 0.91 (0.12) nmol per hemicornea in normal corneas (p < 0.001). Fast blue B staining disclosed that the tissue damage occurred primarily on the surface of the ablated cornea. Conclusion - The presence of lipid peroxidation in the superficial corneal stroma in excimer laser treated corneas was demonstrated. This lipid peroxidation could be from oxygen free radicals generated by the infiltrating polymorphonuclear cells at the site of tissue damage.