Timolol and Aqueous Humor Outflow in Healthy Eyes
American Journal of Ophthalmology, June 2019
Kazemi et al. assessed the effect of timolol on outflow facility in healthy human eyes. They found that the drug reduces outflow facility—and that this effect is greater in eyes with higher outflow facility at baseline.
For this prospective study, the researchers evaluated 113 participants who were 40 to 81 years old. At baseline, intraocular pressure (IOP) was measured in both eyes of each participant in both a sitting and supine position. Outflow facility was measured while participants were in a supine position. The participants were instructed to instill timolol 0.5%, one drop every 12 hours in both eyes, for one week. At that point, IOP and outflow facility measurements were repeated.
The mean IOP at baseline was 15.1 ± 3.0 mm Hg; this decreased to 12.4 ± 2.4 mm Hg after one week of timolol. Mean outflow facility at baseline was 0.23 ± 0.08 μL/min per mm Hg; this decreased to 0.18 ± 0.08 μL/min per mm Hg after the treatment week. In addition, higher baseline outflow facility was associated with greater decrease in outflow facility after timolol treatment.
This reduction in outflow facility may partially negate the overall IOP-lowering effect of timolol, the authors noted. Although the precise mechanism behind this phenomenon remains to be determined, one possible explanation may involve the blockade of beta-receptors in the trabecular outflow pathway. Alternatively, compensatory physiologic changes may be involved.
The original article can be found here.