Abstract
Purpose: :
Photooxidative damage has been proposed as a potentially fundamental factor in the etiology of age-related macular degeneration (AMD). Because damage is largely restricted to the macula, we hypothesize that over a lifetime, the cumulative light flux on the retina may be greater in this central region than in the surrounding peripheral region where damage tends to be less severe. The purpose of our study was to test our hypothesis by using an eye-tracker to measure the cumulative distribution of light on the retina over extended periods of time.
Methods: :
In this study we used a lightweight, head-mounted eye-tracker (Arrington Research®). The system records the coordinates of the subject’s gaze position and pupil size every 16 ms by detecting both the center of the pupil and the corneal reflex. The subject, wearing the eye-tracker, viewed an image displayed on a 16-inch computer monitor. Head position was maintained using a dental bite. Following calibration, the subject, who was naïve with regard to the experiment, was instructed to gaze freely at a 1024×762 pixel grayscale image, such as an outdoor scene, displayed on the monitor. The viewing time ranged from 2 to 10 min. Based on the subject’s gaze position and the light distribution in the monitor screen, we were able to calculate the corresponding light distribution on a ~20o×14o area of the retina around the fovea. The procedure was repeated for each gaze position, allowing us to determine the cumulative light distribution on the retina by adding the individual distributions. Ten subjects (ages 17~22) participated in the study, and 4 different images were presented to each subject.
Results: :
Relative retinal light distributions were obtained with each of the 4 images for all 10 subjects. The data were quantified by running horizontal and vertical line-scans through the point corresponding to the fovea. In the majority of the subjects, retinal light distributions peaked in the foveal region and decreased towards the periphery.
Conclusions: :
For the conditions under which this study was performed, the method shows promise as a relatively simple and fast means of assessing the distribution of light on the human retina. Our results indicate that subjects tend to spend more time gazing at bright regions in the environment, leading to a long-term exposure of the retina to light that is higher in the foveal region. The results provide additional evidence for the role that light may play in the development of AMD. Future work will encompass different viewing situations including videos and more natural outdoor recordings captured by a "scene camera" that forms part of the eye-tracker system.
Keywords: age-related macular degeneration • radiation damage: light/UV • brightness and lightness