Aqueous humour concentration and the intraocular pressure-lowering effect of topical betaxolol before cataract surgery

Objective: The aim was to study the relationship between aqueous humour 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. The 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 surgery. The pupil was dilated in all eyes prior to surgery. The IOP was measured 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 undilated 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 radioreceptor assay. Results: Betaxolol did not decrease IOP significantly in eyes with pupillary dilation. Both betaxolol and placebo decreased IOP 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 instillation. Measurable concentrations of betaxolol were also detected in aqueous humour in group 4a 47.7 h after drug administration. Conclusion: No correlation between aqueous humour concentration of betaxolol and the effect on IOP was found in eyes where the pupil was dilated before surgery. A single betaxolol dose did not decrease IOP significantly in patients undergoing cataract surgery, but the IOP decreasing effect was, however, clearly seen in patients who did not receive mydriatic drugs. The routine use of topical betaxolol prior to cataract surgery to decrease IOP is not recommended.