Effects of Central Corneal Thickness on the Efficacy of Brimonidine and Latanoprost.

Abstract

Abstract: : Purpose: To determine the effect of central corneal thickness (CCT) on the intraocular pressure (IOP) effect of brimonidine and latanoprost in patients diagnosed with ocular hypertension (OHT). Methods: Enrolled in this study were 99 OHT patients on no ocular medications. At baseline, CCT was measured by slit–lamp pachymetry and IOP was determined by pneumatonometry. One eye of each patient received either latanoprost 0.005% once–daily in the evening (baseline IOP of 19.5±0.5 mmHg, mean±SEM; n=50) or brimonidine 0.2% twice–daily (baseline IOP of 20.7±0.5 mmHg; n=49). The fellow eyes received the appropriate vehicle in a randomized, masked fashion. Measurements were repeated at one week. The patients were divided on the basis of average CCT of both eyes at baseline; the Thin Cornea Group had CCTs of <540 µm (n=28 for latanoprost; n=23 for brimonidine) and the Thick Cornea Groups had CCTs of ≥540 µm (n=22 for latanoprost; n=26 for brimonidine). IOP and CCT were compared between corneal thickness groups with unpaired t–tests. Within group comparisons were made with paired t–tests. A correlation between IOP and CCT was evaluated with linear regression. Results: At baseline, the IOPs were not different between corneal thickness groups within each treatment group, or between treated and control eyes. After one week of treatment, both brimonidine and latanoprost significantly (p<0.001) reduced IOP, with no effect on CCT. Mean IOP three hours after the last dose of brimonidine was significantly (p=.001) lower in the Thin Cornea Group (14.0±0.5 mmHg) than in the Thick Cornea Group (16.5±0.5 mmHg). With latanoprost treatment, there was no difference (p=.7) in IOP (15 hours after the last dose) between Thin (15.0±0.6 mmHg) and Thick (15.3±0.6 mmHg) Cornea Groups. There was a slight negative correlation between corneal thickness (mean of baseline and treatment CCT) and IOP change with treatment (R² =0.04, p=.16) in the brimonidine–treated eyes which did not exist in the latanoprost–treated eyes (R² =0.00, p=.96). Conclusion: Following treatment with brimonidine, but not with latanoprost, eyes with thinner corneas had lower IOPs than eyes with thicker corneas.

Keywords: cornea: clinical science • intraocular pressure