Weekly subconjunctival injections of 4mg repository betamethasone, repeated over three weeks, produced a sustained increase of intraocular pressure (IOP) in 96% of the treated rabbits. Treatment was generally well tolerated and important systemic toxic effects were present only in a few animals. The ocular hypertension so obtained was constant, well reproducible and sensitive to antiglaucoma drugs. The authors believe they have developed an animal model which is very suitable for testing the pressure-lowering effect of drugs and for other studies on ocular hypertension and glaucoma.
Lacrimal function was studied in 30 patients treated for glaucoma, with 0.25% timolol eye drops. Rose bengal and fluorescein staining disclosed punctate epithelial defects in 11 eyes after one week. During the following weeks there defects disappeared spontaneously in most eyes. Schirmer tests (I and II), tear lysozyme and pre-corneal film break-up time were significantly decreased by the treatment, while tear immunoglobulins were unimpaired. The authors conclude that topical timolol treatment decreases tear production. This effect is quantitatively limited and does not appear dangerous for normal eyes, although it may become so for eyes with an originally low lacrimal secretion.
The intraocular pressure lowering effects of nine beta-adrenergic receptor blocking agents were compared using two different models of experimental ocular hypertension in rabbits. All the nine drugs possess, to different extents, a clear pressure-lowering action after topical administration into the conjunctival sac. For potency and duration of action, the best results were obtained with timolol and sotalol. Pindolol, oxprenolol, practolol, and propranolol are also fairly potent while less impressive effects were produced by atenolol, butidrine, and metoprolol. With the exception of propranolol, all the drugs were well tolerated by the ocular tissues.
The ocular hypotensive action of labetalol, a drug endowed with alpha- and beta-adrenergic receptor-blocking properties, was studied in both rabbit and human eyes. In the rabbit, using two different models of experimentally induced ocular hypertension, an impressive decrease of IOP was seen after topical administration of the drug. In this species labetalol was found to be at least as effective as timolol and more active than pilocarpine or propranolol. In human eyes suffering from glaucoma, however, its effectiveness was much less evident and clearly inferior to that of timolol.
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