Steroid-induced ocular hypertension in normal cattle.

OBJECTIVES To determine whether the bovine eye develops elevation of intraocular pressure (IOP) in response to topical corticosteroid use and to develop a reliable model of steroid-induced elevation of IOP in an animal. METHODS Intraocular pressure was monitored by Perkins applanation tonometry in a group of 12 cows receiving topically administered prednisolone acetate in 1 eye 3 times a day for a period of 49 days after the establishment of baseline IOP values. Perkins readings were converted to IOP in mm Hg using calibration curves derived from in vitro cannulation manometric experiments and validated with in vivo manometric measurements. Intraocular pressure was also monitored for 50 days after the discontinuation of corticosteroid therapy. RESULTS Intraocular pressure began to increase after 3 weeks of treatment in 100% of the cow eyes receiving corticosteroid and reached a peak 1 week later. Peak interocular IOP differences between the corticosteroid-treated eye and the fellow control eye reached up to 15 mm Hg and began to decline after the discontinuation of treatment but remained significantly elevated for a period of 3 more weeks. CONCLUSIONS Bovine eyes exhibit a robust steroid-induced ocular hypertensive response, with 100% occurrence in this trial. The IOP elevation caused by corticosteroid slowly subsides after discontinuation of treatment. Clinical Relevance The mechanisms of steroid-induced glaucoma may be related to those involved in primary open-angle glaucoma and could provide the clues to elucidate the pathogenesis of the latter. The high prevalence of corticosteroid-induced elevation of IOP in the cow and the large amount of tissue available will permit studies on the mechanism of this phenomenon not previously possible.