Hydrostatic pressure of the suprachoroidal space

The hydrostatic pressure of the suprachoroidal space was measured in 18 cynomolgus monkey eyes by one of two methods: (1) direct cannulation, or (2) silicone sponge implantation. The intraocular pressure (IOP) and suprachoroidal pressure were monitored simultaneously with the IOP being held at various levels between 5 and 60 mm Hg. In eyes with direct cannulation, at an IOP of 15 mm Hg, the pressure in the anterior suprachoroidal (supraciliary) space was 0.8 +/- 0.2 mm Hg (n = 6, mean +/- SE) below the IOP, but the posterior suprachoroidal pressure was 3.7 +/- 0.4 mm Hg (n = 8) below the IOP. The suprachoroidal pressure in eyes with silicone sponge implant was 4.7 +/- 0.6 (n = 7) mm Hg below the IOP. A change in IOP produced a corresponding change in the supraciliary space pressure. However, the pressure difference between the anterior chamber and the posterior suprachoroidal space increased at higher IOP. This pressure differential is the driving force for uveoscleral outflow.