Effect of long-term topical betaxolol on tissue circulation in the iris and optic nerve head

The effect of long-term topical betaxolol on tissue circulation in the iris and optic nerve head was studied. Twenty microliters of 0.5% betaxolol ophthalmic solution was instilled in one eye of an albino rabbit and the same amount of physiological saline in the fellow eye twice daily for 20 days. A quantitative index of tissue blood velocity, NE value, was measured in the iris (21 rabbits) and optic nerve head (31 rabbits) of both eyes before the first instillation and 2 hr after completion of instillations, using a laser speckle tissue circulation analyser of which details have been reported previously. The intraocular pressure was also measured at 5-day intervals. The intraocular pressure was lowered by 2-3 mmHg only in the betaxolol-treated eye (P < 0.01). Both in the iris and optic nerve head no significant bilateral difference in the NE was seen before the first instillation, while it was significantly greater in the betaxolol-treated than in the contralateral control eye by about 10% after completion of instillations (P < 0.02-0.05). The difference between the NE after completion of instillations and that before the first instillation was significantly greater in the betaxolol-treated eye than in the contralateral control eye both in the iris and optic nerve head (P < 0.001-0.02). Twenty-day twice daily instillation of 0.5% betaxolol caused relatively small, but significant increase in tissue blood velocity in the ipsilateral iris and optic nerve head in albino rabbits, which may have clinical implications. (C) 1997 Academic Press Limited.