PURPOSE: Epidemiologic studies have shown that the onset of cortical cataract occurs primarily in the inferonasal human lens and that the incidence of cortical cataract is correlated with ultraviolet light. Ray tracing analysis has suggested that the peripheral cornea concentrates light on the opposite peripheral lens and that the nose and orbit block peripheral light, except temporally, resulting in a relative concentration of light on the inferonasal lens. Studies were performed to test 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 exposed to summer sunlight at various times of day, with and without sunglasses. Discs from the different experimental groups were scanned, and the digitized images were analyzed densitometrically using image analysis software. RESULTS: With the head upright, the inferonasal section of the disc exhibited the most intense exposure under all lighting conditions. Sunglasses decreased the intensity of overall light exposure but did not eliminate the inferonasal bias. Only blocking the temple eliminated this effect. CONCLUSIONS: This model supports the idea that the peripheral cornea focuses light on the inferonasal portion of the human lens. These results may explain the correlation between light and the location of cortical cataract.
PURPOSE: Epidemiologic studies have shown that the onset of cortical cataract occurs primarily in the inferonasal human lens and that the incidence of cortical cataract is correlated with ultraviolet light. Ray tracing analysis has suggested that the peripheral cornea concentrates light on the opposite peripheral lens and that the nose and orbit block peripheral light, except temporally, resulting in a relative concentration of light on the inferonasal lens. Studies were performed to test 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 exposed to summer sunlight at various times of day, with and without sunglasses. Discs from the different experimental groups were scanned, and the digitized images were analyzed densitometrically using image analysis software. RESULTS: With the head upright, the inferonasal section of the disc exhibited the most intense exposure under all lighting conditions. Sunglasses decreased the intensity of overall light exposure but did not eliminate the inferonasal bias. Only blocking the temple eliminated this effect. CONCLUSIONS: This model supports the idea that the peripheral cornea focuses light on the inferonasal portion of the human lens. These results may explain the correlation between light and the location of cortical cataract.