Effect of various drugs on pseudofacility and aqueous humor formation in the rabbit eye.

Norepinephrine and epinephrine reduce aqueous humor formation by an amount less than sufficient to reduce the intraocular pressure. Both drugs increase pseudofacility and true outflow facility which both contribute to reduce the pressure. Neither drug changes the value of x_c, the pressure index of the capillaries, which indicates that large hemodynamic changes do not occur. Phenylephrine has no effect on pseudofacility, since, although x_c is reduced, the fluid permeability is increased in a compensatory manner: an increase in true outflow facility is responsible for the small pressure fall.Pilocarpine causes a minor increase in aqueous humor formation, has no effect on pseudofacility yet lowers the intraocular pressure, albeit by only 2 mmHg. In order to lower intraocular pressure, therefore, pilocarpine must increase true outflow facility.Prostaglandin E₁ increases intraocular pressure, aqueous humor formation, x_c and pseudofacility. PGE₁ is known to induce venous congestion and this correlates with the increase in x_c since a secondary rise in capillary pressure would follow. The increase in aqueous humor formation accounts for the increase in intraocular pressure. The increase in pseudofacility accounts for about half of the increase in total outflow facility found with PG's, at least at times up to 2 hr after topical PG application.