In this article, we highlight a method that probes the directional sensitivity of cones, in particular those in the fovea. Directional sensitivity is a unique property of cones, i.e. it is not shared by any other retinal element, and can be taken as a measure of the health of cones. In a group of healthy subjects, the directional reflection was 1.78%. In early age-related macular degeneration (AMD), despite a healthy-looking fovea, the mean directional reflection was 0.92%; in late AMD, the figure decreased further to 0.86%. These findings point to a malfunctioning of the outer segments. In addition, the method yields an estimate of the optical density of macular pigment. In early AMD, the macular pigment did not differ from normal; this finding did not point to a protecting role of macular pigment in AMD.
Migration of an outer retinal element in a healthy child followed by longitudinal multimodal imaging
