Age-related macular degeneration (AMD) is a disease with multiple risk factors, underlying many of which appears to be oxidative damage. Because of the presence of photosensitizers in the retina, much of the oxidative damage may be owing to the relatively intense, short-wavelength, focused light to which the retina is subjected. Our long-term goal is to gain a deeper understanding of the opposing roles of light and the eye's defense mechanisms in the etiology of AMD. That the damage which AMD inflicts is quite localized raises the question of whether light, integrated over a lifetime, falls uniformly on the retina, or is more concentrated, like the disease, in the macula. Our objective is to develop a technology with which we will measure the cumulative light distribution on the human retina over extended periods of time. Our hypothesis is that the distribution will reach a maximum in the central macula. This hypothesis is based on the observation that bright objects in the environment tend to attract our visual attention and are thereby imaged in the center of the macula. Our specific aims are to develop an eye-tracking system with which to measure the cumulative light distribution on the retina under conditions in which subjects freely view still images, movies and, ultimately as we refine the method, the environment around them. At a given instant, the distribution of light on the retina is determined by the distribution of light in the scene being observed, the subject's gaze position in the scene, and the size of the eye's pupil. Preliminary studies have demonstrated the feasibility of our approach using an eye-tracking system. The relevance of, and rationale for, these studies is that knowledge of the distribution of light on the retina would provide us with an understanding of the association between excessive ambient light and the risk for AMD, and an explanation of why the eye has evolved mechanisms to limit damage by light in the central macula. In succeeding studies, it will be our intention to make a transition to a fully portable system so that the same measurements can be made under a variety of conditions, e.g., driving, sitting in front of a computer or television, or different outdoor activities. The successful completion of these studies will amplify our knowledge of the etiology of AMD and one of its modifiable risk factors - light. Relevance: Age-related macular degeneration (AMD) is the leading cause of blindness in the USA, with the number of those afflicted estimated to rise from the current ~ 2 million to ~ 3 million by the year 2020. While the etiology of AMD is not well understood, excessive environmental light, which is a modifiable risk factor, appears to play a role. The current proposal seeks to advance our knowledge of AMD in this area and thereby highlight the importance of eye protection against the damaging effects of light, for example, through the use of sunglasses and appropriate dietary supplements.