Purpose:
Age-related macular degeneration results in damage in the area surrounding the fovea, and light may be a risk factor. The study was to develop a method to measure the cumulative distribution of light on the human retina over extended periods of time in order to see whether the distribution peaks in the fovea.
Methods:
In this study we used a head-mounted eye-tracker system, made by SensoMotoric Instruments. This system records the x-y coordinates of the subject’s gaze position by detecting both the center of the pupil and the corneal reflex. The subject, wearing the eye-tracker, views an image displayed on a monitor. A dental bite was provided to maintain head position. Following calibration, the subject was presented with a visual image such as Fig. 1a. The x-y coordinates of the corners of the image were recorded and then the subject was instructed to maintain the gaze within the white circle at the center of the image. Based on the subject's gaze position, and the distribution of light on the monitor screen we were able to calculate the corresponding light distribution on a ~ 18°×12° area of the retina around the fovea. This procedure was done for each gaze position, allowing us to determine the cumulative light distribution on the retina by simply adding the individual distributions. The procedure was repeated but now the subject was presented with the image shown in Fig. 2a. In this case, any gaze position that fell outside the red rectangle was automatically eliminated by the program.
Results:
Fig.1b shows the relative retinal light distribution obtained with the test image shown in Fig. 1a. The fovea is at the center. The data was quantified by running a horizontal line-scan through the point corresponding to the fovea (Fig 1c). Fig 2b and 2c show the light distribution and the line-scan respectively corresponding to the test image shown in Fig. 2a. In both cases the light distribution presents a peak at the fovea.
Conclusions:
The method shows promise as a novel, simple and fast means of measuring the distribution of light on the human retina. Our preliminary results indicate that a subject's gaze tends to favor bright regions in the environment resulting in a higher light flux on the foveal area.
Keywords: radiation damage: light/UV • age-related macular degeneration • brightness and lightness