Modification of Finite Element Model to Anatomy and Physiology of Human

To determine the implications of changing conditions which may affect drug distribution in the vitreous in a more clinically relevant setting, the finite element model can be modified to match the geometry of the human eye (21) (Fig. 7). The most significant differences between the posterior segment of a rabbit and human eye are the size of the lens and the volume of the vitreous humor. In a human eye, the lens occupies a smaller portion of the vitreous than in the rabbit eye. The volume of the vitreous humor in the human eye is approximately 4 mL, and the volume of the rabbit vitreous is approximately 1.5 mL. Another difference between the human and rabbit eye is the flow dynamics in the posterior aqueous humor chamber. The volumetric flow rate of aqueous humor is similar in human and rabbit eyes; however, the cross-sectional area for flow is approximately four times larger in human eyes, resulting in a lower flow velocity in human eyes. Similar to the rabbit eye model, fluorescein and fluorescein glucuronide were used as test compounds to study the effects of injection position and volume in the human eye model. In humans, the exact retinal permeabilities of fluorescein and fluorescein glucuronide are not known, so the values used were 2.6 x 10~5 cm/s and 4.5 x 10~7 cm/s, respectively, which are the average of the values that were found using the rabbit eye finite element model. For the purpose

Figure 7 Cross-section view of human eye model. The model was based on the physiological dimensions of the human eye. The posterior chamber of the aqueous humor was included to account for the loss of drug from the vitreous across the hyaloid membrane. Transport of drug by convection and diffusion was accounted for in the posterior chamber of the aqueous humor, and only diffusive transport was accounted for in the vitreous humor.

Figure 7 Cross-section view of human eye model. The model was based on the physiological dimensions of the human eye. The posterior chamber of the aqueous humor was included to account for the loss of drug from the vitreous across the hyaloid membrane. Transport of drug by convection and diffusion was accounted for in the posterior chamber of the aqueous humor, and only diffusive transport was accounted for in the vitreous humor.

of examining the effects of changing intravitreal injection variables, the accuracy of the retinal permeability is not of prime importance. The retinal permeability value will impact the quantitative results of each injection variable case studied, but qualitative intercase comparisons using a constant retinal permeability will be valid.

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