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W. J. Foster, P. Fok, T. Chou; Nutrient Diffusion Through Subretinal Implants. Invest. Ophthalmol. Vis. Sci. 2007;48(13):653.
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There are numerous sub-retinal therapeutic implants being proposed for the treatment of retinal diseases. These proposed therapies include electronic retinal prostheses, neurotransmitter-releasing retinal prostheses, scaffolds for retinal pigment epithelium regeneration, and drug-delivery systems. Inherent in these systems is a limitation in diffusion of nutrients from the choriocapillaris, which is thought to supply the outer two-thirds of the retina. We propose that full-thickness holes, machined through the implant, will provide a substantial portion of the nutrients without compromising the mechanical integrity of the implant.
A calculation of the diffusion of nutrients through the proposed machined holes was performed. The analysis utilizes known boundary conditions at the choriocapillaris and at the implants.
We find that, provided that full-thickness holes are created through the implant, there exists significant diffusion of nutrients through a solid sub-retinal implant, even if the total area of the holes is small when compared with the total implant area.
We find that nutrient diffusion through an implant is sensitive to not only the total area of the holes, but critically on the distribution of holes. Surprisingly, provided the holes are uniformly spaced, a small hole area fraction is sufficient to allow almost half the nutrient diffusion that would be present if the implant were not present. This unexpected result allows the mechanical and functional integrity of sub-retinal implants to be maintained while allowing significant diffusion of nutrients through the implant.
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