Effect of DMSO and exchange volume on outflow resistance washout and response to pilocarpine during anterior chamber perfusion in monkeys.

PURPOSE: To determine the dependence of outflow resistance washout on anterior chamber (AC) fluid exchange volume (EV); the minimum EV required for complete AC mixing, and the effect of 0.01-5% DMSO in the exchange solution on outflow resistance.
METHODS: Total outflow facility was determined in 63 pentobarbital-anesthetized cynomolgus monkeys, before and after AC exchange, for 10 min, with 1, 2, and 4 ml of Bárány's perfusand, containing 0.01-5% DMSO or containing 1 microgram/ml or 5 micrograms/ml pilocarpine HCL (pilo), each volume.
RESULTS: Post-exchange facility increased by 21% (p < 0.05) vs. baseline for both the 1 and 2 ml Bárány's volumes and by 50% (p < 0.001) for the 4-ml volume. Washout-corrected post-exchange facility was unchanged from baseline, following 1 or 2 ml exchange with 1 microgram/ml pilo; 5 micrograms/ml pilo increased facility by 130 +/- 41% and 174 +/- 40% respectively, relative to baseline. Exchange with 4 ml of 1 microgram/ml pilo increased facility 72% more than the 2 ml (p < 0.029) and 100% more than the 1 ml (p < 0.014) volumes. When corrected for their respective baselines, 2 ml of 5 micrograms/ml pilo increased facility 12.7 +/- 4.4% more than the 1 ml volume (p < 0.05). Post exchange facility was not significantly increased over baseline in eyes exchanged with 2 ml of 0.01-4% DMSO or in eyes exchanged with Bárány's alone. When corrected for their respective baselines, post-exchange facility was significantly lower in eyes exchanged with 5% DMSO vs. Bárány's (p = 0.022).
CONCLUSIONS: One- and 2-ml EVs preserve outflow resistance equally well, and substantially better than 4 ml. Two ml is the minimum volume necessary for adequate mixing of AC drug solutions, to achieve the full facility effect. Concentrations of DMSO up to 4% in a 2-ml EV can solubilize compounds without additionally decreasing outflow resistance.