Effect of Timolol on Aqueous Humor Dynamics in the Rabbit

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Abstract
The effects of timolol and several reference agents upon intraocular pressure (IOP), outflow facility and aqueous humor formation, were investigated in rabbits. Consistent with their proposed mechanisms of action, norepinephrine and epinephrine (1% topically) lowered IOP and increased outflow facility, whereas, acetazolamide (100 mg/kg i.v.) and isoproterenol (1 % topically) lowered IOP without affecting outflow facility. At the same doses, acetazolamide, but not epinephrine, reduced aqueous humor formation. Timolol (1 % topically) reduced IOP, reduced aqueous humor flow and did not alter outflow facility. The data suggest that in rabbits, as in man, timolol lowers IOP primarily by reducing the formation of aqueous humor.