The canine eye: in vitro dissolution of the barriers to aqueous outflow

Facility of aqueous outflow and time-dependent changes in its hyaluronidase-sensitive and hyaluronidase-resistant components were evaluated in freshly excised canine eyes by constant pressure quantitative aqueous perfusion. Mean baseline facility of outflow was 0.24 microliter/min/mm Hg. With prolonged perfusion at constant intraocular pressure, facility of outflow was observed to increase almost linearly for at least 3 hr and continued to increase for up to 10 hr, reaching a maximum several times the initially measured facility. Perfusion with pooled dog aqueous humor did not prevent the time-dependent increase in measured facility. Rapid exchange of anterior chamber contents with perfusion solution alone produced an immediate threefold increase in facility, again followed by a gradual time-dependent facility increase. Rapid exchange of anterior chamber contents with hyaluronidase produced an immediate fivefold increase in facility with stabilization of measured facility over 3 hr and subsequent perfusion. The time-dependent changes in measured facility of outflow or "washout phenomenon" appeared to result from the gradual dissolution of the hyaluronidase-sensitive component of the barriers to aqueous outflow in the canine eye.