ABSTRACT
Light exposure has been implicated in age-related macular degeneration (AMD). This study was designed to measure cumulative light distribution on the retina to determine whether it peaked in the macula. An eye-tracker recorded the subject's field of view and pupil size, and superimposed the gaze position. Fifteen naïve subjects formed a test group; 5 formed a control group. In phase 1, all subjects viewed a sequence of photographic images. In phase 2, the naïve subjects observed a video; in phase 3, they performed computer tasks; in phase 4, the subjects walked around freely. In phase 1, control subjects were instructed to gaze at bright features in the field of view and, in a second test, at dark features. Test group subjects were allowed to gaze freely for all phases. Using the subject's gaze coordinates, we calculated the cumulative light distribution on the retina. As expected for control subjects, cumulative retinal light distributions peaked and dipped in the fovea when they gazed at bright or dark features respectively in the field of view. The light distribution maps obtained from the test group showed a consistent tendency to peak in the macula in phase 3, a variable tendency in phase 4, but little tendency in phases 1 and 2. We conclude that a tendency for light to peak in the macula is a characteristic of some individuals and of certain tasks. In these situations, risk of AMD could be increased but, at the same time, mitigated by the presence of macular carotenoids.
Subject(s)
Light , Retina/metabolism , Carotenoids/metabolism , Fovea Centralis/metabolism , Fovea Centralis/radiation effects , Humans , Macula Lutea/metabolism , Macula Lutea/radiation effects , Macular Degeneration/etiology , Macular Degeneration/metabolism , Macular Degeneration/prevention & control , Retina/radiation effectsABSTRACT
We have developed an objective procedure, using a modified retinal camera, to determine macular pigment (MP) optical density distributions in the human retina. Using two multi-band filters, reflectance maps of the retinas of young subjects (<25 years old) were obtained at 460, 528, 610 and 670 nm, without pupil dilation. The log-transformed maps were combined linearly to yield optical density maps of MP, cone and rod photopigments, and melanin. MP optical density and heterochromatic flicker photometry results for 22 subjects were in reasonable agreement. Cone photopigments, like MP, showed similar, well-defined peaks at the fovea, whereas rod photopigment showed a minimum. Melanin was more broadly distributed.
Subject(s)
Macula Lutea/chemistry , Melanins/analysis , Retinal Pigments/analysis , Adult , Dark Adaptation , Humans , Image Processing, Computer-Assisted , Photic Stimulation , Photography , Video RecordingABSTRACT
Heterochromatic flicker photometry is commonly used to measure macular pigment optical density (MPOD) in the human retina. It has been proposed, and accepted by many, that the MPOD so measured represents the value at a retinal location corresponding to the edge of the flickering, circular stimulus. We have investigated this proposal by using a series of annular stimuli to determine the MPOD distribution in the central 1.5 degrees of the retina for both eyes of 10 subjects. The MPOD obtained using a 1.5 degrees circular stimulus matched the MPOD distribution at a retinal eccentricity that was always less than the stimulus radius, and averaged, for the 10 subjects, 51% of the stimulus radius. Similar results were obtained using a 1 degrees stimulus. Thus the edge hypothesis is inconsistent with our data. We suggest that involuntary eye movements may be responsible for an apparent edge effect.
