Changes in outflow facility in experimental hyphema.

To characterize the pathophysiology of hyphema clearance, we studied changes in the facility of outflow in experimental hyphema in freshly enucleated rabbit eyes. Hyphemas, with washed normal or sickled red cells (RBCs) (suspended in isotonic phosphate buffer to obtain a hematocrit value comparable to that of whole blood) and occupying 50% to 100% of the anterior chamber volume, caused a marked cell "crowding" in the chamber angle and an increase in the outflow resistance; the facility stabilized at a value 60% lower than the control (p = < 0.001). No significant change in outflow facility was observed in hyphemas of either RBC type occupying 25% of the anterior chamber volume (p = N.S.). Whole blood hyphema occupying 50% of the anterior chamber volume reduced the facility of outflow by 80% of the control mock aqueous value (p = < 0.001); a comparison with 50% hyphema produced by washed RBCs indicated a significant contribution by the plasma (fibrin) component (p = 0.0025) in increasing the resistance to outflow.