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Ulrich Schraermeyer, Sigrid Schultheiss, Theo Oltrup, Thomas Bende, Sebastian Schmelzle, Alexander Tschulakow; Unravelling the mystery of the Stiles Crawford Effect. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5603.
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© ARVO (1962-2015); The Authors (2016-present)
The Stiles Crawford Effect of the first kind (SCE I) was regarded as one of the most important discoveries in visual science of the last century. The SCE describes the phenomenon that light entering the eye near the edge of the pupil produces a lower photoreceptor response compared to light of equal intensity entering near the center of the pupil. The reduction in the photoreceptor response is significantly greater than would have been expected from a mere reduction in the photoreceptor acceptance angle of light entering near the edge of the pupil, but its cause is still not understood.
Serial ultrathin and semithin sections were made through human foveolae and used to construct 3D models of central Müller cells. In addition, we used human foveae from flat mounted isolated retinae and measured the transmission of collimated light under the light microscope at different angles.
We found extremely large Müller cells in the central foveola (200 µm in diameter) in which cell organelles are rarely present. We discovered that when the light enters the fovea directly, there is a very bright spot exactly in this area which is composed only of cones and Müller cells. However, when the angle of the transmitted light was changed to 10 degrees, the bright foveolar center became dark and the SCE-like phenomenon became directly visible (Fig. 1). Measurements of the intensities of light transmission in the central foveola for incident angles 0 and 10 degrees resemble the relative luminance efficiency for narrow light bundles as a function of the location where the beam enters the pupil as reported by Stiles and Crawford. The effect was observed in all human foveae and persisted in one fovea after carefully brushing away the outer segments.
Here we show that unique Müller cells in the center of the fovea guide the light based on the incident angle by their specific anatomy and thereby reduce light transmission through the retina, probably causing the SCE of the first kind.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Fig. 1: A human foveolar center is shown (lower panel) in translucent light entering at 0, 5 and 10 degrees respectively with the correspondent measurements of light intensities (upper graph).
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