OUTFLOW CHARACTERISTICS OF ISOLATED ANTERIOR SEGMENTS OF HUMAN EYES

Purpose. To evaluate the relationship between intraocular pressure (IO P) and flow through the trabecular meshwork in isolated anterior segme nts of human eyes. Outflow facility (C) is thought to decrease proport ionally with increasing IOP in human eyes in vivo and in vitro. Method s, Twenty-nine eviscerated human anterior segments were perfused with ascending and descending pressure sequences in a stepwise fashion (ran ge, 4 to 40 mm Hg); ii of the 29 eyes were treated similarly after 20 hours of perfusion at 12 mm Hg. Pressure-flow sequences of individual eyes were evaluated with a linear (constant C) and a nonlinear regress ion method (C decreasing with increasing IOP). In addition, in eight i ntact postmortem eyes, pressure-flow characteristics were determined, followed by perfusion of their isolated anterior segments. Results. Pr essure-flow sequences as determined by linear regression had an averag e correlation coefficient of 0.99, Average C (slope of the plot) was 0 .26 +/- 0.03 mu l minute(-1) mm Hg-1 There was no influence of directi on of pressure sequence or time on C. To test for linearity, the hypot hetical outflow obstruction coefficient (Q) was determined for each pl ot. Median Q of 29 eyes was 0.003 mm Hg-1, and in 45% (13 eyes) Q was negative, suggesting facilitation instead of obstruction. This indicat es that the outflow obstruction coefficient is not a physiological par ameter in isolated anterior segments. Conclusions, The relationship be tween IOP and flow through perfused isolated anterior segments of huma n eyes is linear between 4 and 40 mm Hg: indicating that within this r ange outflow facility is constant and does not decrease with increasin g IOP.