Effect of timolol on aqueous humor protein concentration in the human eye

We performed a double-masked, controlled study investigating the increase in the protein concentration in aqueous humor after topical timolol maleate administration. Forty patients scheduled to undergo intracapsular cataract surgery were included in the study. Either timolol ophthalmic solution or the vehicle of timolol alone (control) were applied topically in a randomized fashion, and aqueous humor was collected during surgery. Protein concentrations were determined by gel-filtration chromatography. The total protein concentration as well as the concentration of high and medium molecular weight proteins were significantly elevated in the timolol-treated group. The relation of the levels of the three different molecular weight classes did not differ significantly between the two groups, indicating that undisturbed protein filtration in the face of reduced aqueous humor production--and not a change in the permeability of the blood-aqueous barrier--is responsible for the increase in concentration.