Effects of Topical Phenylephrine and Tafluprost on Optic Nerve Head Circulation in Monkeys with Unilateral Experimental Glaucoma

Abstract

To compare the effects of a topical alpha agonist (vasoconstrictor) and a prostaglandin receptor (FP) agonist (vasodilator) on circulation in the optic nerve head (ONH) in experimental glaucomatous and normal eyes of monkeys. Tissue blood velocity in the ONH (NB(ONH)) was determined using the laser speckle method in both eyes of eight normal cynomolgus monkeys under systemic anesthesia for 180 minutes after bilateral instillation of 5% phenylephrine. The effect of 0.0015% tafluprost, a potent FP agonist, was also studied after single and once-daily 7-day instillations. Measurements were repeated in both eyes of the eight monkeys after establishment of unilateral laser-induced glaucoma. NB(ONH) decreased significantly in both eyes of normal monkeys 30 to 120 minutes after phenylephrine instillation by a maximum of 9% to 11% (P < 0.05) without significant change in intraocular pressure (IOP). A similar decrease in NB(ONH) was found in non-laser-treated eyes in glaucomatous monkeys despite the absence of significant changes in contralateral experimental glaucomatous eyes. NB(ONH) increased by 16% (P < 0.05) 60 minutes after a single instillation and also after 7-day repeated instillations of tafluprost in both eyes of normal monkeys. A similar increase in NB(ONH) occurred in both eyes after the establishment of unilateral glaucoma but was completely abolished by 5 mg/kg indomethacin injected intravenously 15 minutes after tafluprost instillation. Tafluprost significantly reduced IOP only in experimental glaucomatous eyes by 34%. The ONH vasculature in glaucomatous and normal eyes reacts differently to an exogenous alpha agonist, whereas it reacts similarly to an FP agonist.