Effect of topical betaxolol on tissue circulation in the human optic nervehead

There have been no reports to date on long-term betaxolol instillation effe cts on the human optic nerve head (ONH) tissue circulation. The purpose of this study was to study the effect of topical 0.5% betaxolol on tissue bloo d velocity in the human ONH. Using a laser-speckle tissue blood flow analyz er, normalized blur (NB; a quantitative index of tissue blood velocity) was measured every 0.125 seconds at a temporal ONH site free of visible surfac e vessels. Measurements were averaged for 3 cardiac cycles (NBONH). For bas eline comparison (day 0), recordings of bilateral NEONH and intraocular pre ssure (IOP), blood pressure (BP) and pulse rate (PR) were recorded in healt hy volunteers before, and 2, 4.5, and 7 hr after, instillation of 30 mu L o f betaxolol vehicle, and again on day 21; IOP was also recorded on days 7 a nd 14. On day 1 (the day after baseline measurements), and twice daily for 3 weeks, 30 mu L of 0.5% betaxolol into one eye and 30 mu L vehicle was ins tilled into the other in a double-blind study. Measurements as on day 0 wer e again recorded on day 21; IOP was also recorded on days 7 and 14. During baseline recordings, no significant changes were noted in any parameters. A fter administration of topical betaxolol, IOP was significantly reduced, bi laterally, with greater reduction in the betaxolol-treated eyes on day 21. Also on day 21, the NEONH of the betaxolol-treated eyes was significantly h igher 4.5 hr after instillation than that of the comparable baseline record ing (p=0.035 with Bonferroni's correction); BP, PR, and NEONH in the eye wh ich received only the vehicle showed little change. Tissue blood velocity i n the human ONH was increased at least temporarily by instillation of topic al betaxolol twice daily for 3 weeks. Although the obtained increase is sma ll and may be clinically insignificant, the potential of betaxolol that can affect the ONH tissue circulation in humans after 21 days of instillation is thought to deserve further investigation.