Modifications to Finite Element Model to Simulate Aphakic Eyes

Although cataract extractions previously involved removal of the entire lens, it is more common today to leave the posterior lens capsule intact in order to reduce postoperative complications such as vitreous changes and retinal detachment (34). To study elimination in an aphakic eye, the human phakic eye model was modified so that the curved barrier formed by the lens (Fig. 7) was replaced by the posterior capsule of the lens (Fig. 13). All of the other tissues of the aphakic eye model were assumed to be in the same

Figure 13 Cross-section view of aphakic human eye model.

configuration as in the phakic eye model. The values noted earlier for the retinal permeability of fluorescein and fluorescein glucuronide were also used in the aphakic model to study the effects of removing the lens on the elimination of compounds that have either a high or a low retinal permeability. The diffusivity of fluorescein and fluorescein glucuronide used for the vitreous and hyaloid membrane was 6.0 x 10~6 cm2/s, which is the same as the diffusivity in free solution (35). Kaiser and Maurice (30) studied the diffusion of fluorescein in the lens and concluded that the mass transfer barrier formed by the posterior capsule of the lens was the same as an equal thickness of vitreous. The drug diffusivity used within the posterior lens capsule, therefore, was also 6.0 x 10~6 cm2/s.

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