AQUEOUS-HUMOR CONCENTRATION AND THE INTRAOCULAR PRESSURE-LOWERING EFFECT OF TOPICAL BETAXOLOL BEFORE CATARACT-SURGERY

Objective: The aim was to study the relationship between aqueous humou r betaxolol concentration and intraocular pressure (IOP). Methods: In this double-blind, randomized study, we administered betaxolol (a) or placebo (b) ocularly to 131 patients scheduled for cataract surgery. T he patients were randomly divided into ten groups. In groups la and Ib , the drug was scheduled to be instilled 1-2 h, in groups 2a and 2b 12 h, in groups 3a and 3b 24 h, and in groups 4a and 4b 48 h before surg ery. The pupil was dilated in all eyes prior to surgery. The IOP was m easured with Perkins' applanation tonometer before the instillation of the drug and just before the peribulbar block. Twenty microlitres of 0.5% betaxolol or placebo solution was instilled into the eye. IOP was also measured before instillation of the drug and after 1-2 h in undi lated eyes of 20 patients, whose contralateral eye was to be operated on, to rule out the effect of pupil dilation on IOP (groups 5a and 5b) . Aqueous humour betaxolol concentrations were analysed using a radior eceptor assay.Results: Betaxolol did not decrease IOP significantly in eyes with pupillary dilation. Both betaxolol and placebo decreased IO P significantly in patients without pupillary dilation, the effect of betaxolol being slightly more pronounced. The betaxolol concentration in aqueous humour was 731 ng.ml(-1) in group 1a, 2.4 h after drug inst illation. Measurable concentrations of betaxolol were also detected in aqueous humour in group 4a 47.7 h after drug administration. Conclusi on: No correlation between aqueous humour concentration of betaxolol a nd the effect on IOP was found in eyes where the pupil was dilated bef ore surgery. A single betaxolol dose did not decrease IOP significantl y in patients undergoing cataract surgery, but the IOP decreasing effe ct was, however, clearly seen in patients who did not receive mydriati c drugs. The routine use of topical betaxolol prior to cataract surger y to decrease IOP is not recommended.