Posterior drainage of intraocular fluid: an experimental approach on bovine cadaver eyes

We evaluated the posterior drainage of saline in cadaver bovine eyes using different experimental procedures. The saline perfusion via a pars plana infusion into the vitreous cavity was measured in the following 5 different groups of 20 enucleated bovine eyes: 1, control; 2, vitrectomy; 3, vitrectomy + retinectomy; 4, vitrectomy + retinectomy + removal of retinal pigment epithelium (RPE); and 5, vitrectomy + retinectomy + removal of RPE + choroidectomy. The mean values obtained for the facility of saline outflow were as follows group 1, 0.0458 microliter min-1 mmHg-1; group 2, 0.0393 microliter min-1; group 3, 0.1308 microliter min-1 mmHg-1; group 4, 0.2288 microliter min-1; and group 5, 0.9985 microliter/min-1 mmHg-1. The retina appeared to be the major barrier to fluid movement from the vitreous to the chorioid, perhaps due to the lack of extracellular space and to the tight and impervious structure of the retina. The barrier function of the retina may explain the hypotony seen after rhegmatogenous retinal detachment and the decrease in intraocular pressure observed after the removal of silicone oil in eyes that had undergone retinectomy. Our results suggest that the reduction in intraocular pressure occurring after retinectomy is attributable to the new drainage pathway.