Adequacy of exchanging the content of the anterior chamber

Perfusion studies of the anterior segment of the eye frequently involve an exchange of the contents of the anterior chamber. We here determined how much fluid was necessary to pass through the upstream tubing and anterior chamber such that the contents of the anterior chamber were adequately exchanged. We used fluorescein dextran (500 kD) to assess the adequacy of exchange of enucleated porcine eyes that were washed out with varying volumes of buffer. The results were compared with two theoretical models, one that accounted for the convective dispersion that occurs in the upstream tubing while in the other, more simple model, it was assumed that the upstream tubing and anterior chamber behave essentially as a well-mixed chamber. We found that the experiment results were bounded by these two models, with the well-mixed model giving a lower bound on the rate at which the anterior chamber can be cleared. We found that exchange of the anterior chamber to reduce the concentration of a drug or tracer by 20-fold required a perfused volume three times the combined volume of the upstream tubing and anterior chamber.