Pressures in the anterior ciliary arteries, choroidal veins and choriocapillaris

A micropuncture technique was used to measure the pressure in the anterior ciliary arteries of monkeys as well as the pressures in the choroidal veins and in the choriocapillaris of rabbits. Monkeys were used to measure the pressure in one of the anterior ciliary arteries at three different points, First at a scleral 'well', and then at 2 and 5 mm from the same 'well'. It was found that the pressures recorded increased proportionally to the distance from the scleral 'well'. Afterwards the intraocular pressure (IOP) was increased stepwise and the arterial pressure was measured at each increment (from spontaneous IOP to 50 cmH2O). When compared, it was found that an increase in IOP was not followed by a statistically increased anterior ciliary artery pressure. The pressure in the choroidal veins and the choriocapillaris was measured in rabbits through a scleral window positioned between the two superior veins at about 4 mm from the nearest. The pressure recorded in the choroidal vein was found to be 3.3 +/- 0.4 cmH2O higher than the spontaneous IOP (20.3 +/- 1.6). However, when the IOP was increased stepwise it was found that this difference diminished as the value for the IOP neared the arterial pressure. Thus, the pressure gradient for flow from the intermediate-seized choroidal veins to the intraocular origin of the vortex veins is only a few cmH2O under normal conditions and is reduced at very high intraocular pressures at which the blood flow is markedly reduced or stopped.(ABSTRACT TRUNCATED AT 250 WORDS)