Effects of latanoprost and timolol-XE on hydrodynamics in the normal eye.

Purpose

To compare the effects of latanoprost and timolol-XE on ocular pressure and perfusion in healthy adults, with respect to episcleral venous pressure.

Methods

A double-masked, placebo-controlled crossover study of weeklong bedtime treatment with one drop of drug, with placebo contralaterally, followed by a 3-week washout and alternate-drug/contralateral-placebo repeat. Intraocular pressure was measured by applanation and by pneumotonometry, providing pulsatile ocular circulatory estimates. Measurements of episcleral venous pressure were obtained (Friberg method).

Results

Twenty subjects participated (five men, 15 women; mean age, 39 years (range, 21 to 55 years); mean baseline intraocular pressure, 13.4 mm Hg). A greater decrease in intraocular pressure was seen among these subjects the morning after initiating treatment with latanoprost (-2.0 mm Hg; P <.0001) than with timolol-XE (-0.9 mm Hg; P =.051) (latanoprost versus timolol DeltaP =.008). This ocular hypotensive effect remained significant that evening with latanoprost (-3.2 mm Hg; P <.0001) but not with timolol XE (-1.0 mm Hg; P =.2). By the morning of day 8, mean intraocular pressure remained 3.2 mm Hg below baseline with latanoprost and 2.3 mm Hg below baseline with timolol-XE (P <.0001 for both drugs). Neither drug altered episcleral venous pressure. Among a subgroup of nine subjects with comparable intraocular pressure reductions with the two drugs, latanoprost treatment was associated with a 16.7% increase in mean pulsatile ocular blood flow (P =.04) through the weeklong treatment interval, consistently higher than during timolol-XE treatment of the same subjects.

Conclusion

Latanoprost caused an overnight decrease in intraocular pressure in normotensive normal eyes, and both drugs significantly reduced intraocular pressure within 1 week. Intraocular pressure remained higher than episcleral venous pressure throughout treatment with both drugs. Latanoprost was associated with enhanced pulsatile ocular perfusion not seen with timolol-XE treatment.