F. Richard Christ

Evaluation of the chemical, optical, and mechanical properties of elastomeric intraocular lens materials and their clinical significance

ABSTRACT The current trend toward small incision cataract surgery has resulted in the use of elastomers as intraocular lens materials. Little has been published on appropriate methods of evaluating biomaterials intended for implantation in the eye. We present a methodology for such a study and report the results for two elastomeric silicone intraocular lens materials. The chemical, optical, and mechanical properties of the two materials were evaluated, as was their stability to hydrolytic and ultraviolet degradation. Qualitative correlations between these properties and clinical requirements are discussed. Both silicone materials possessed the necessary properties for use as small incision intraocular lenses.

Accelerated hydrolytic and ultraviolet aging studies on SI-18NB and SI-20NB silicone lenses

ABSTRACT This report describes the results of in vitro accelerated hydrolytic and ultraviolet aging studies performed on SI‐18NB and SI‐20NB silicone intraocular lenses. The hydrolytic aging study simulated the effects of 20 years in vivo. The ultraviolet aging study simulated the effects of 17 years in vivo. No significant changes in the focal length and resolution of the lenses were observed. Examination of the lens surfaces using scanning electron microscopy revealed in changes in surface morphology.

Moisture droplet formation on the posterior surface of intraocular lenses during fluid/air exchange

Abstract We investigated the conditions under which moisture droplets would form on intraocular lens (IOL) posterior surfaces during fluid/air exchange procedures in rabbits implanted with silicone or poly(methyl methacrylate) (PMMA) IOLs. Moisture droplets did not form when the posterior capsule was intact, regardless of IOL material or infusion fluid temperature. If a capsular tear was present, droplets formed with both IOL materials when balanced salt solution (BSS®) at ambient temperature was used as the infusion fluid. This effect was significantly more pronounced with silicone IOLs, resulting in an immediate loss of visualization of the fundus. In these cases, visualization was quickly restored by applying a viscoelastic to the posterior IOL surface.

Accelerated ultraviolet aging of intraocular lens optic materials: A 50 year simulation

Purpose: To introduce an updated accelerated photoaging model for application to intraocular lens (IOL) materials and to apply this model to determine the photostability of AMO® PhacoFlex® model SI‐18NGB and PhacoFlex® II model SI‐20NGB silicone IOL materials over a simulated 50 years of exposure. Setting: Research laboratory, AMO Surgical Products, Irvine, California, USA. Methods: Previous photoaging models and aging parameters, including intraocular exposure intensity, daily exposure duration, and acceleration exponent were critically reviewed and analyzed, and an updated model was introduced. The test specimens were continuously irradiated with ultraviolet (UV) light in a Suntest UV chamber at an intensity of 8 mw/cm2 for 86 days to simulate 50 years of in vivo exposure. The silicone lenses were evaluated for focal length, resolution, and surface integrity, while regular slabs were tested for tensile strength, elongation, hardness, contact angle, and percentage light transmission. The UV‐absorption capacity was monitored using ultrathin slabs (0.127 mm). Six replicate samples were used for each determination, and a two‐sided t‐test with significance set at P < .05 was used to evaluate the difference before and after aging. Results: No significant difference in optical, physical, and surface properties of the lenses and lens materials was found. No change in UV‐absorption capacity was observed after a simulated 50 years of accelerated photoaging. Conclusion: The AMO PhacoFlex SI‐18NGB and PhacoFlex II SI‐30 NGB silicone lens materials resisted UV light degradation over 50 years of simulated exposure.