Eight Years Experience With Permalens® Intracorneal Lenses in Nonhuman Primates

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Abstract
For the past 8 years, three independent laboratories have been researching the biocompatibility and performance of Permalens intracorneal lens implants in the corneas of nonhuman primates. Both myopic and hyperopic corrections have been achieved. This article describes the evolution of the intracorneal lens design and manufacturing process. During this time period, 63 surgeries were performed on various species of nonhuman primates. Follow-up examination extended between 30 months and 8.2 years. Objective measures of refractive performance, as well as biocompatibility were made using slit lamp, retinoscopy, autorefractor, specular microscope, etc. Additionally, histopathology was performed on many of the specimens, both acute and chronic. Surgically successful implants were achieved in between 60% and 100% of eyes in the various series of lens implants outlined in the article. Levels of contamination in the preparation of hydrogels were felt to be responsible for many of the surgical failures. The removal of silicone and other contaminants seems to have significantly improved the biocompatibility of these materials within the cornea. The major histopathological finding was that there appeared to be some epithelial thinning over the implants, but in general excellent biocompatibility was obtained over the 8-year period outlined in this paper. Although extensive studies of biocompatibility have been completed, the future of the performance of these materials remains to be proven in the human subject. Additionally, empirical relationships between lens implant power and refractive results will have to be determined in humans, prior to their general clinical usage.