The loss of fluorescein, fluorescein glucuronide and fluorescein isothiocyanate dextran from the vitreous by the anterior and retinal pathways.
The pathways by which fluorescein (F), fluorescein glucuronide (FG) and fluorescein dextran (FD) leave the vitreous body of the rabbit were examined by measuring the concentration distribution of the injected fluorophores in sections of the frozen eyes. The contours of F, as already known, show that it leaves the vitreous predominantly across the retinal surface. Mathematical analysis of the concentration gradient leads to an average outward permeability coefficient of 1.4 x 10(-3) cm min-1 for the retinal layers. The contours of FG and FD show that they leave predominantly by diffusion into the posterior chamber, encountering only a minor barrier at the anterior hyaloid membrane. The anterior contours indicate that there can be no substantial posteriorly directed fluid flow through the vitreous; if it occurs its velocity across the retinal surface must be less than 2 x 10(-5) cm min-1. The contours of FD near the posterior pole of the retina suggest that such a flow may be taking place. Some time after the systemic administration of F, an analysis of the rate of loss of fluorescence from the vitreous body shows that this corresponds to the movement of FG out through the anterior chamber. Its value bears little relationship to the condition of the blood-vitreal barrier.