The effect of topical timolol on epinephrine-stimulated aqueous humor flow in sleeping humans.

PURPOSE It has been shown that intravenously administered epinephrine can increase the rate of aqueous humor flow in sleeping humans. This experiment was conducted to determine if this stimulatory effect can be blocked by the beta-adrenergic antagonist timolol. METHODS Twenty normal human subjects were studied for one sleep cycle at night. Epinephrine was infused intravenously at a rate of 1 microgram/min. One eye received a single drop of 0.25% timolol, and the fellow eye received a placebo. Aqueous humor flow was measured by the rate of disappearance of fluorescein from the eye. RESULTS The rate of aqueous humor flow was 14% lower in the timolol-treated eye than in the placebo-treated eye during 6 hours of sleep. This difference was interpreted as being due to blockage of part of epinephrine's effect on aqueous humor flow by topical timolol. CONCLUSION It was concluded that the effect of systemically administered epinephrine on aqueous humor flow is at least partly mediated locally on the eye and that some portion of timolol's well-known effect on daytime aqueous humor flow could be due to inhibition of the ocular effects of epinephrine.