Retention of reversibly thermo-gelling timolol on the human ocular surface studied by video meniscometry

PURPOSE: To investigate the retention of reversibly thermo-gelling timolol (TG-timolol) on the human ocular surface using video meniscometry. METHODS: The study population consisted of 14 healthy volunteers with no external eye disease. Fifteen microl TG-timolol were instilled into one eye of each subject and the same volume of aqueous, timolol ophthalmic solution was instilled in the fellow eye, in a masked fashion. Tear meniscus curvature was monitored at the center of the lower meniscus in each eye, using a newly-developed video meniscometer, before and at one-minute intervals for ten minutes after, the instillation. The radius of meniscus curvature (R) was calculated from printed video-images using the concave mirror formula. The change in R with time after instillation was compared for the two groups. RESULTS: The change in meniscus radius with time t [defined as deltaR(t) = R(t) - R(0)] showed a significant exponential regression in both the TG-timolol and the timolol groups. There was a significant difference in the value of deltaR(5) and deltaR(10) between eyes with TG-timolol [deltaR(5) = 0.29 mm, deltaR(10) = 0.18mm] and eyes with timolol only [deltaR(5) = 0.10mm, deltaR(10) = 0.06 mm] [deltaR(5): P < 0.001, deltaR(10): P < 0.001]. The area under each regression curve of deltaR(t), an indicator of vehicle retention, was greater in the eyes treated with TG-timolol than in those receiving timolol only (2.09 vs. 0.56, P < 0.001). CONCLUSIONS: The present study demonstrated that the reversibly thermo-gelling timolol was better retained at the ocular surface than conventional, aqueous timolol.