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Effect of topical beta-blockers on tissue blood flow in the human optic nerve head
Purpose:
To study the effect of topical 0.5% timolol and 2% carteolol on tissue blood flow in the human optic nerve head (ONH).
Methods:
Using a laser speckle tissue blood flow analyzer, normalized blur (NB), a quantitative index of tissue blood velocity, was measured every 0.125 s in the temporal site of the ONH free of visible surface vessels and averaged over 3 cardiac pulses (NBONH). To serve as a baseline, NBONH and intraocular pressure (IOP) in both eyes, blood pressure (BP) and pulse rate (PR) were recorded in healthy volunteers before, 1.5, 3 and 4.5 hrs after a 30L instillation of the vehicle of timolol or carteolol. From the following day and twice daily for 3 weeks, 30L of either 0.5% timolol or 2% carteolol was instilled into one eye and the respective vehicle into the fellow eye in a masked manner. NBONH, IOP, BP and PR were again recorded on the 21st and last experiment day. IOP was also recorded on the 7th and 14th days. Carteolol concentration in the plasma was also recorded after instillation of carteolol on the 21st day.
Results:
During the baseline experiments, all the parameters recorded showed no significant change. After topical timolol, IOP was significantly reduced bilaterally with more reduction in the timolol-treated eye. Bilateral NBONH, BP and PR showed little change on the 21st day. After topical carteolol, IOP was significantly reduced bilaterally with more reduction in the carteolol-treated eyes on the 21st day. NBONH in the carteolol- and vehicle-treated eyes was significantly higher on the 21st day than recorded in the same eye in the baseline experiment (P = 0.013 and 0.047), while BP and PR showed little change. The maximum carteolol concentration in plasma at 3 hrs on the 21st day averaged 1294 pg/ml.
Conclusions:
Results indicated that 3-week twice daily topical timolol treatment had no deleterious effect on the ONH tissue blood flow in the human eye, and that 3-week twice daily topical carteolol treatment may increase the tissue blood flow in the human ONH.