Effects of topical phenylephrine on blood flow in the posterior segments of monkey and aged human eyes

Purpose: The aim of this study was to evaluate the effects of topical 5% phenylephrine on circulation in the optic nerve head (ONH) of cynomolgus monkeys and in the central retinal artery (CRA) of aged patients. Methods: In five monkeys, ONH tissue blood velocity (NBONH), determined using the laser speckle method, and intraocular pressure (IOP), blood pressure (BP), and pulse rate (PR) were measured 2 h after a single unilateral instillation and after a 7-day twice-daily unilateral instillation of phenylephrine. In 20 aged patients (mean age: 70.4 years), the CRA circulation indices were determined by color Doppler imaging (CDI), and IOP, BP, and PR were measured before and after four serial unilateral instillations at 30-min intervals of phenylephrine. Results: In the monkeys, there was no significant change in IOP, BR, or PR, while NBONH decreased 2 h after a single instillation (P = 0.080) and after a 7-day instillation (P = 0.043). In theaged patients, IOP in the phenylephrine-treated eyes significantly increased (P = 0.022), while the CDI indices, BR, and PR did not. In this CDI assessment, the statistical power to detect significant changes (P < 0.05) in the resistive index was estimated as 4.8% of the standard deviation. Conclusions: Topical phenylephrine decreased the ONH tissue blood velocity in monkeys, suggesting possible risks regarding circulation in the posterior portion of the eye. However, these effects were not observed in the CRA circulation in the patients. (C) Japanese Ophthalmological Society 2004.