Araie and Maurice (8) used the simplest approach to model distribution and elimination in the vitreous by representing the vitreous as a sphere with the entire outer surface representing the retina (Fig. 1). The predicted concentration profile within the vitreous will be the same for any cross section that passes through the center of the sphere, with the highest concentration in the center and the lowest concentration next to the outer surface. In a rabbit eye, the center of curvature of the retina is immediately next to the lens, on the symmetry axis of the vitreous. Qualitatively, the concentration profile calculated by a spherical model will be correct for the posterior hemisphere of the vitreous, which is behind the center of curvature of the retina. In a spherical geometry model like the Araie and Maurice model, the concentration profile in the anterior hemisphere will be the same as in the posterior hemisphere, since the two hemispheres are the same. Therefore, the concentration profile calculated by a spherical model for the portion of the vitreous that is in front of the center of curvature of the retina will not accurately reflect the actual profile that would be present in vivo. A spherical model also assumes that there is no flux across the plane that passes through the center of curvature of the retina and is perpendicular to the symmetry
Model of Model of
Araie and Maurice Yoshida et al
Model of Ohtori and Tojo
Figure 1 Comparison of models developed by Araie and Maurice (8), Yoshida et al. (12,13), and Ohtori and Tojo (10,11).
axis. For this assumption to be true, the loss across the portion of the retina located behind its center of curvature must equal the sum of the loss across the hyaloid membrane plus the loss across the portion of the retina in front of the center of curvature of the retina. This condition will only be true for a particular retinal permeability.
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