Abstract
PURPOSE. To build an improved apparatus for measuring outflow facility by one- and two-level, constant pressure perfusion. METHODS. A computer-controlled and -monitored tower adjusts the height of a fluid reservoir by a stepper motor every 5 min, to keep intraocular pressure (IOP) constant at one or two desired pressure levels (e.g. 2.5 and 12.0 mm Hg above the spontaneous IOP). The fluid flow rate is calculated by the equation Q = (Pres 2 IOP)/R, where Pres is the pressure of the reservoir as calculated by the term "rgh," h being the height of the reservoir, measured by the rotation of stepper motor, g, the gravity constant, and r, the fluid density. IOP is measured by the transducer, and R is the resistance of 180 mm tubing. Outflow facility is calculated by ?Q/?P. ?Q is the difference between flow rate at the two pressure levels, and ?P is the intraocular pressure difference. Perfusion was performed on live albino rat eyes by the two-level constant pressure technique, and on artificial steel eyes at a single constant pressure perfusion (20 mm Hg). RESULTS. Outflow facility of albino rat eyes and artificial steel eyes perfused for 40 and 30 min, respectively was 0.0507 ± 0.0039 µl/min/mm Hg and 0.3546 ± 0.0034 µl/min/mm Hg (mean ± SD), respectively. CONCLUSIONS. Our perfusion apparatus is highly stable, sensitive, and capable of measuring subtle changes in outflow facility in vivo and in vitro.
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