Problems of Peripheral Vision

The Topography of Vision in Mammals of Contrasting Life Style: Comparative Optics and Retinal Organisation

“…A morphologic explantation attempts only to deal with extreme photopic conditions and cannot encompass the functional reorganisation of the retina. The illumination sensitivity of the acuity curves also introduces the possibility of obtaining low peripheral acuity readings because of the reduction in illumination intensity arising with oblique-ray incidence and the reduced apparent pupil size (WEALE, 1956). It is characteristic of attempts to account for acuity in anatomic terms that only retinal structure is considered, but it is obviously possible that subsequent stages in the visual pathway set their own limitations, and this has been demonstrated to occur.…”

“…The results of CAMPBELL and GREEN (1965) indicate that optic attenuation signifIcantly limits the human contrast sensitivity for high spatial frequencies imaged at the fovea. Because the human eye resembles a Gaussian system to the extent that its image quality deteriorates with increasing eccentricity from the optic axis (see WEALE, 1956), it follows that the neural potential of the fovea to achieve low-contrast sensitivity thresholds at high-spatial frequencies would ideally be optimal upon fusion of the visual and optic axis; in man they diverge by only 6° (HELMHOLTZ, 1924). If the achievement of such fusion is the primary adaptation in frontality, the fabric of the optical and neural apparatus remaining unchanged, then restriction of the panoramic field to the rear of the head follows as a necessary consequence.…”

Information capacity of eyes

“…At an eccentricity of 70" (temporal on retina), the highest photopic acuity corresponds to A4 z 0.5" for a grating test pattern and A9 z 0.8" for a Landolt C test object (Weale, 1956;Pirenne, 1962;Le Grand, 1967). Furthermore, Mandelbaum and Sloan (1947) show that the acuity of the peripheral retina (beyond 20" eccentricity) is relatively insensitive to changes in retinal illuminance, as in the rod monochromat studied by Hecht et al (1948).…”

Visual resolution in the periphery

“…Not only does the retinal illumination vary with the dilation and contraction of the pupil, but as the viewing angle is increased, the horizontal dimension oft he pupillary aperture decreases, reducing the amount of light reaching the retina. In acuity work, the size and shape of the pupil have an added importance in determining the diffraction pattern on the retina, and Weale (1956) has shown that this pattern becomes distorted as the result of the elliptical pupil at large viewing angles. While it is unlikely that acuity in the periphery is limited by the diffraction pattern on the retina (Kerr, 1969), eliminating the variation in the retinal light distribution for different viewing angles is desirable.…”