Variations in photoreceptor directionality across the central retina

Abstract

Cones show a differential sensitivity to light coming from different portions of the pupil, typically being most sensitive to light from the center of the pupil. We measured the directional properties of the cones across the central 6 deg of the retina, using an optical imaging technique. We find that the cones in the center of the fovea have the broadest tuning. The width of the angular tuning changes rapidly from 0 deg to 1 deg retinal eccentricity, with cones at 1 deg being much more narrowly tuned than the cones in the center of the fovea. Directional tuning of the cones remains relatively constant from 1 deg to 3 deg retinal eccentricity. Receptoral disarray contributes minimally to the measured directional properties of the foveal cones, and there is no evidence of asymmetry between horizontal and vertical retinal locations. There are only small differences among the five subjects in the change in angular tuning of the cones with retinal location. We find that at the foveal center the directional tuning of the cones is limited by the diameter of the cone apertures.

Model for cone directionality reflectometric measurements based on scattering

“…Burns et al 9 showed that values changed rapidly with retinal eccentricity, with the width of the pupil intensity distribution being broader at the center of the fovea than at higher eccentricities. We measured as a function of retinal eccentricity (0 deg and 0.5, 1, 2, and 3 nasal and temporal) for 543 nm and compared the results with the predictions from the simulation.…”

“…[1][2][3][4][5][6][7][8][9] The principal aim of these techniques is to provide objective information on a given aspect of the visual system rapidly and reliably and in a manner that is well tolerated by both normal subjects and patients. Generally, one can get the same information with traditional psychophysical techniques, but the reliability and time saving of the objective techniques make it desirable for eventual clinical purposes.…”

“…Different groups have used slightly different approaches. For example, Van Blockland 10 measured the scattering diagrams as the exit pupil was scanned along one axis; Gorrand and Delori 11 scanned both the entry pupil (for illumination) and the exit pupil (for light collection); Burns et al 6,9 imaged the entire distribution of the light returning from the retina through the pupil for any given pupil entry position; and Delint et al 12 analyzed digitized images of the fundus reflectance obtained with a scanning laser ophthalmoscope for different pupil entry locations.…”

“…In what follows we will concentrate on the implementation by Burns et al 6,9 Figure 1 sketches the basic idea of the technique. A small retinal patch is illuminated from a small laser spot imaged in the plane of the eye's pupil.…”

Adaptive optics scanning ophthalmoscopy with annular pupils

“…Despite the photoreceptor reflectance fluctuations [11,41,42] and other sources of variability such as image registration, tear film and subject alignment, the observed reflectance amplitude values (shown in Table 2 ) are consistent with the SCE predictions. Table 2 Measured relative average image intensities for images collected with constant PMT gain compared against predicted values (in parenthesis) according to the SCE measured objectively at fixation (ρ = 0.11 mm ) [43]. A Gaussian intensity ...…”