The aqueous humor dynamics and the biphasic response in intraocular pressure induced by guanethidine and adrenaline in the glaucomatous eye

Continuous administration of guanethidine (3%) and adrenaline (0.5%) in one eyedrop (GA) induced a biphasic response of intraocular pressure (IOP). In ten patients with primary open angle and seven glaucoma suspects treated with (GA) twice daily during a 7 month period, tonography, and tonometry were performed and the pupil diameter measured 3 and 8 h post-GA. The combined data of both groups in the hypertensive phase, showed an IOP increase of 2.8 mm Hg (P < 0.05), an unchanged coefficient of the outflow, dilated pupil (1.73 mm) (P < 0.005) and a 36% increase of aqueous humor production (P < 0.02). The specific biphasic course of IOP during treatment with GA seems to be caused by fluctuations in aqueous humor production. The increase in aqueous rate during the hypertensive phase could be related to secondary (rebound) vasodilation in the ciliary body and/or to a transient disruption of the blood-aqueous barrier induced by release of prostaglandins.