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Abstract

When looking at a bright white surface through a 0.5 mm pinhole quickly moved close to one's eye on a circular path, the shadows of `mouches volantes' are flitting too fast across the retina to be detected. Instead, shadows of those structures are perceived which are close above the photosensitive layer: capillaries surrounding the foveola, and between them `leather-like structures' (v.Campenhausen, Die Sinne des Menschen, 1993) consisting of tiny bright dots. We determined their spatial frequency psychophysically by comparing it with that of a small flock of painted dots. When viewed through the excentrically rotated pinhole, both spatial frequencies are perceived simultaneously and they appear equal from a well-defined distance. Thus, on the retina the dots must be about 15 mm apart, which coincides with the size of cone cells. We hypothesise that the dot pattern represents the `shadows' of the cone cells' nuclei, each of which operates as a tiny ball lens, owing to its higher refractive index. When looking through a microscope with an excentrically rotating aperture stop, this dot pattern is seen all over the bright field, since the image-forming cone of rays steadily hits the retina from different directions. In ophthalmology, this pattern may serve to diagnose a beginning to the degeneration of one's own macula. [Supported by the Deutsche Forschungsgemeinschaft.]