EXPERIMENTAL-MODEL OF LIGHT FOCUSING OF THE PERIPHERAL CORNEA

Purpose. Epidemiologic studies have shown that the onset of cortical c ataract occurs primarily in the inferonasal human lens and that the in cidence of cortical cataract is correlated with ultraviolet light, Ray tracing analysis has suggested that the peripheral cornea concentrate s light on the opposite peripheral lens and that the nose and orbit bl ock peripheral light, except temporally, resulting in a relative conce ntration of light on the inferonasal lens. Studies were performed to t est these theories, Methods. A model cornea and anterior chamber, set on a disc of light-sensitive paper, was placed in the orbit of a human skull coated with wax to simulate soft tissue. The ''eye'' was expose d to summer sunlight at various times of day, with and without sunglas ses, Discs from the different experimental groups were scanned, and th e digitized images were analyzed densitometrically using image analysi s software. Results. With the head upright, the inferonasal section of the disc exhibited the most intense exposure under all lighting condi tions, Sunglasses decreased the intensity of overall light exposure bu t did not eliminate the inferonasal bias. Only blocking the temple eli minated this effect. Conclusions. This model supports the idea that th e peripheral cornea focuses light on the inferonasal portion of the hu man lens. These results may explain the correlation between light and the location of cortical cataract.