EFFECTS OF TIME OF STORAGE, ALBUMIN, AND OSMOLALITY CHANGES ON OUTFLOW FACILITY (C) OF BOVINE ANTERIOR SEGMENT IN-VITRO

Purpose. To analyze the influence of time of storage, the presence of albumin at physiological concentrations, and the perfusion with anisos motic media on the aqueous humor outflow facility (C) of isolated bovi ne anterior segments (AS). Methods. Anterior segments dissected from c ow eyes were perfused at a constant pressure of 10 mm Hg with Dulbecco 's modified Eagle's medium (DMEM; osmolality 300 mOsm/kg), with hyposm otic media (150, 210, and 270 mOsm/kg), or with hyperosmotic media (36 0, 420, and 480 mOsm/kg). Outflow facility was calculated every 5 seco nds as the ratio between average inflow from the reservoir (in microli ters per minute) and the perfusion pressure (in millimeters of mercury ). Three groups were studied: a 0-hour group, with AS perfused with DM EM 1 to 3 hours after enucleation; a 0-hour alb-group, with AS perfuse d with DMEM plus 0.1 mg/ml albumin 1 to 3 hours after enucleation; and a 24-hour group, with AS per-fused after storage for 24 hours in DMEM . In the 0-hour groups, perfusion with increasingly hyposmotic or hype rosmotic media was also made in 30-minute steps, followed by a return to isosmotic medium for 90 minutes. Results. Perfusion of AS with DMEM for 9 hours caused a progressive increase in C that was statistically significant at 225 minutes in the 0-hour group perfused with DMEM and at 195 minutes in the 24-hour group perfused with DMEM. The 0-hour al b-group perfused with DMEM did not show changes in C throughout the 9- hour perfusion period. Perfusion with increasingly hyposmotic media in duced a progressive decrease in C that did not recover on return to is otonic medium. Hyperosmotic media caused a progressive increase in C t hat returned to control values when isotonic medium was again perfused . Conclusions. Preservation of tissue for C measurements is best achie ved with short storage time (1 to 3 hours). Physiological concentratio ns of albumin (0.1 mg/ml) prevent development of washout, suggesting t hat albumin or an albumin-bound factor in aqueous humor may play a rol e in the maintenance of outflow resistance. Outflow facility also may be influenced by volume changes in the trabecular meshwork.