Purpose: To investigate the impact of argon laser trabeculoplasty (ALT) on endothelin-1 (ET-1) concentration of aqueous humour and intraocular pressure (IOP) in the rabbit.
Methods: Standard ALT was performed on one eye of 19 pigmented rabbits. A modified treatment in which the laser light was focused on the inner limbal surface (argon laser scleroplasty, ALS) was also performed on one eye of a further 15 rabbits. IOP was measured with a Tono-Pen-2 tonometer before treatment, under general anaesthesia. Post-laser IOP measurements followed by aqueous humour aspiration were performed under general anaesthesia 4, 24 and 120 hours after treatment. IOP readings were considered relative values, since the tonometer was calibrated to the human eye and not to the rabbit eyeball. Different groups of animals were used for the tests after each time period. The groups of 4 hours time consisted of 9 animals which had undergone ALT and 5 which had undergone ALS. All the other groups consisted of 5 animals each.
Results: In the ALT group IOP decreased following treatment, and the IOP change (a relative change) showed a significant difference between the treated and the control eyes at all three follow-up times (paired t-test, p<0.05), and a significant interaction was found between treatment and follow-up time (ANOVA, p<0.05). Concentration of ET-1 in the aqueous humour of the treated eyes increased by about an order of magnitude 4 hours after ALT, compared to the contralateral control eyes (103.66+/-41.59 pg/ml versus 8.75+/-2.95 pg/ml, Wilcoxon matched pairs test, p<0.01). ET-1 concentration 24 and 120 hours after ALT, however, did not differ significantly from the corresponding contralateral control values. In the ALS group neither IOP change nor aqueous humour ET-1 concentration differed in a statistically significant manner between the treated and control eyes.
Conclusions: The results suggest that ALT is followed by an immediate and short-term increase of aqueous humour ET-1 concentration in the rabbit, probably due to leakage from the uveal tissue.