Stiles–Crawford effect of the first kind: assessment of photoreceptor alignments following dark patching

Abstract

Properties of presumed mechanisms controlling photoreceptor alignments are partially defined. A phototropic mechanism normally dominates alignment, but do modest changes in orientations occur with dark patching? Here, new photopic Stiles-Crawford (SCE-I) determinations were made before patching (pre-patch), just after 8-days of dark-patching (post-patch), and 3 days after patch removal (recovery test). We tested at 0, 11 and 22 degrees in the temporal retina of both eyes. Ten eyes of adult subjects were tested. SCE-I peak positions and Stile's parameter 'rho' were assessed. Dark-patching effects were small. Observations revealed meaningful corrective alignment overshoots with recovery in the light. Results suggest (1) the presence of multiple weak mechanisms affecting receptor alignments in the dark; (2) the phototropic mechanism to be dominant in the light; (3) the need for multiple test loci to be sampled in such studies, and (4) small changes in the SCE-I in the pupil plane can reflect meaningful events occurring at the retina.

Photoreceptor waveguides and effective retinal image quality

“…Although the differences between a waveguided and a retinal image are rather subtle, these details may acquire particular importance once the utmost in terms of resolution is sought either for visual performance 37,38 or in retinal imaging applications with large pupil diameters. 39,40 For example, it is known that photoreceptors can reorient to adapt to changed illumination conditions, 19,20 and it seems therefore likely that photoreceptors may at least be partially adapted to match average ocular aberrations in terms of wavefront slope at the retina in such a way that their light-capturing capabilities become maximized.…”

“…In turn, if a photoreceptor is not well aligned toward the center of the active pupil, the amount of light coupled to it will be expected to decrease. 19,20 The fraction of incident light at the retina that couples to a given photoreceptor (i.e., the coupling strength) and is guided toward its outer segment can be calculated from…”

Directional sensitivity of the retina: 75 years of Stiles–Crawford effect

“…Attempts to change the Stiles-Crawford effect by prolonged occlusion, predicated on the theory that this would lead to a disarray of receptors when deprived of active phototropic influence, have not been conclusive (Kono et al 2001).…”

Directional light scanning laser ophthalmoscope

“…In experiments, the situation can be expected to improve since the small width of the incident beam, together with any fine structure in the focus, may act as a resolution-enhancing filter by favoring the coupling of light to a single photoreceptor at a time and thereby highlighting its contribution. Although such a situation is not controllable for accurate photoreceptor mosaic imaging, it may suffice to reveal areas of misoriented photoreceptors 27 as well as other retinal abnormalities.…”