To determine whether the bovine eye develops elevation of intraocularpressure (IOP) in response to topical corticosteroid use and to develop areliable model of steroid-induced elevation of IOP in an animal.
Intraocular pressure was monitored by Perkins applanation tonometryin a group of 12 cows receiving topically administered prednisolone acetatein 1 eye 3 times a day for a period of 49 days after the establishment ofbaseline IOP values. Perkins readings were converted to IOP in mm Hg usingcalibration curves derived from in vitro cannulation manometric experimentsand validated with in vivo manometric measurements. Intraocular pressure wasalso monitored for 50 days after the discontinuation of corticosteroid therapy.
Intraocular pressure began to increase after 3 weeks of treatment in100% of the cow eyes receiving corticosteroid and reached a peak 1 week later.Peak interocular IOP differences between the corticosteroid-treated eye andthe fellow control eye reached up to 15 mm Hg and began to decline after thediscontinuation of treatment but remained significantly elevated for a periodof 3 more weeks.
Bovine eyes exhibit a robust steroid-induced ocular hypertensive response,with 100% occurrence in this trial. The IOP elevation caused by corticosteroidslowly subsides after discontinuation of treatment.
The mechanisms of steroid-induced glaucoma may be related to those involvedin primary open-angle glaucoma and could provide the clues to elucidate thepathogenesis of the latter. The high prevalence of corticosteroid-inducedelevation of IOP in the cow and the large amount of tissue available willpermit studies on the mechanism of this phenomenon not previously possible.