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M. D. Lowery, M. Ghazizadeh, D. H. Sliney, R. Jain; Photostability of Ocular Biomaterials. Invest. Ophthalmol. Vis. Sci. 2008;49(13):408.
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© ARVO (1962-2015); The Authors (2016-present)
The International Standard for ophthalmic implant biocompatibility includes an assessment of material photostability, but published data on the photostability of ocular biomaterials are limited. The goal of this study was to measure the light transmission of ocular tissues and assess its impact on the photostability model and evaluation of ocular biomaterials. We present the photostability results for hydrophobic acrylic, silicone, polyimide (PI), and polyethersulfone (PES) biomaterials as well as tissue transmission data that affect the photostability model.
Photoexposure studies were performed using the Suntest XLS+ chamber (Atlas Material Testing Technology, LLC). Light intensity was adjusted to 500-750 W/m2 (5-10 mW/cm2 in the UV range). The spectral transmission of ocular tissues from six New Zealand White and six Dutch-Belted rabbits was evaluated using an RSA-BE-65 integrating sphere (diffuse and direct radiation) that was incorporated into a Beckman DU800 spectrophotometer. The rabbit sclera, cornea, and iris were dissected within 3 hours of enucleation.
Silicone and hydrophobic acrylic biomaterials, which comprise the optic body of an intraocular lens, are unaffected by exposure to UV-visible radiation, with exposure times simulating up to 50 years in vivo. PI and PES haptic materials, however, are susceptible to photodegradation. For both rabbit models, less than approximately 10% of the diffuse UV energy was transmitted through the sclera and iris tissues. These findings impact the magnitude assumed for the I1 term in the photostability model, where only the effects of the cornea and aqueous humor are included. The photostability model overestimates the radiation flux at the periphery of the IOL, because a portion of the incident light is absorbed by the cornea, iris, and sclera; and anatomical features that further reduce exposure are all not considered by the model.
Silicone and hydrophobic acrylic IOL materials are stable under UV-visible radiation as tested according to the current photostability model. However, the model may require an adjustment for biomaterials, such as PES and PI, which are intended to be placed behind the iris where the light flux is reduced by approximately 90%.
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