Effects of adrenergic agents on alpha-chymotrypsin-induced ocular hypertension in albino and pigmented rabbits: a comparative study.

Alpha-chymotrypsin-induced ocular hypertension in albino rabbits is widely used as an experimental model to screen potential antiglaucoma drugs. The present study compares the intraocular pressure (IOP) response following the ocular application of single or repeated adrenergic agents in conscious albino and pigmented rabbits. A single instillation of clonidine was not as effective in lowering the IOP in pigmented hypertensive rabbit eyes as in albino hypertensive eyes. Similarly, betaxolol moderately lowered the IOP in albino rabbits but induced a slight response when pigmented rabbits were used as an experimental model. Twice-a-day applications of betaxolol in pigmented hypertensive eyes permitted an identical level of IOP decrease to be reached, as observed in a one-day study in albino rabbits, after at least 6 days of treatment. It has been suggested that the pigmented layers of the iris-ciliary body may act as sites for topically applied antiglaucoma drugs. Non-specific binding could explain in part the frequent discrepancy observed between the preclinical results obtained in albino hypertensive rabbit eyes and clinical results obtained in glaucomatous human eyes.