Changes in Aqueous Nitric Oxide Concentration Following Excimer Laser Corneal Ablation

ABSTRACT

There have been some reports about formation of free radical species in aqueous humor after excimer laser photorefractive keratectomy(PRK). We investigated whether there exists an increase of nitric oxied(NO) level in aqueous humor after excimer laser treatment. Of the 41 albino rabbits(81 eyes) used for this study, 25 eyes served as controls. The remaining 56 eyes were divided into three groups, i.e., a group with its epithelium removed mechanically(3 eyes), -6.0D PRK group(24 eyes) and -12.0D PRK group(29 eyes). After varing time intervals following excimer laser treatment, aqueous NO concentration was determined with ELISA method using Griess reagent. The mean aqueous NO concertration was 101.83ng/ml in normal control group and showed no difference(107.00ng/ml) from that of mechanically abladed group, Aqueous NO was increased 30 min after PRK in both groups compared to normal(-6.0D 218.67ng/ml, -12.0D 198.68ng/ml) and maintained at one hour postoperatively. Eyes with -12.0D ablation still while eyes with -6.0D ablation showed no difference from normal. Six hours after PRK, aqueous NO was returned to the normal level in both groups of PRK. The results of this study showed that excimer laser PRK induced NO production in aqueous humor, and the more extensive amount of excimer laser applied, the longer time would be taken to restore the normal NO level. It seems that such an elevation of NO level could be one of the factors that cause temporary corneal stromal edema or anterior chamber reaction after excimer laser PRK.