Effects of topically instilled drugs on intraocular pressure in rabbits

The effect of the ocular instillation of some drugs on the intraocular pressure of non-anaesthetized rabbits was studied, using the Schiötz tonometer. The risk of systemic absorption of drugs follwoing ocular instillation was evaluated by 1. measuring the spreading of effects from the treated eye to the contralateral one and 2. studying the effects on blood pressure or on blood pressure responses to noradrenaline. The results showed that trazodone, epinephrine and acetazolamide produced hypotension on the treated eye; there was no spreading of effects to the contralateral one. These data could suggest that the primary site of action of these drugs is the eye. Naphazoline reduced the intraocular pressure both on the treated eye and, with a constant delay, on the contralateral one. This was interpreted as a combination of a local action and systemic absorption. The effects of chlorpromazien were more complex. This drug produced hypertension and a strong irritation on the treated eye as well as a hypotensive effect on the contralateral one. The rise in intraocular pressure was probably caused by irritation; the hypotensive effect by systemic absorption. The following drugs were inactive: amphetamine, chlorothiazide and pilocarpine.