Absence of time-dependent facility increase ("washout") in the perfused enucleated human eye

During the course of constant-pressure anterior chamber perfusion experiments in eyes from a number of species, measured outflow facility increases progressively with perfusion time. One possible explanation for this phenomenon has been that the technique of perfusion induces a loss of extracellular material from the outflow pathway. Therefore, this general observation has been termed the "wash-out" effect. Data from the authors' laboratories demonstrate that although outflow facility increases in cynomolgus monkey eyes by 26% and 42% from baseline over 90 minutes in vivo and in vitro, respectively, this does not occur in the enucleated human eye. The absence of washout in the human eye probably cannot be explained by postmortem conditions since enucleated monkey eyes undergo a similar magnitude of washout as the monkey eye in vivo. Furthermore, since washout does not occur in the perfused human infant eye, the age of the donor cannot explain the difference in washout properties between human and other primate eyes. The monkey eye in vivo is a valuable model in the study of outflow physiology. However, the difference in washout behavior between human and other primate eyes may point to a potentially important fundamental difference in the biology of the outflow pathways in these two species.