Psychophysical measurements using achromatic grating resolution acuity
in peripheral vision show a prominent retinal asymmetry in acuity which is
consistent with predicted values based on available estimates of midget
ganglion cell density. Recent studies have shown that peripheral grating
resolution acuity values for short-wavelength-sensitive (SWS) isolating
gratings in normal observers are closely related to predicted values based
on the underlying small bistratified ganglion cell density. By measuring
SWS resolution acuity at different locations across the visual field, we
wished to see if any significant acuity asymmetry exists for the
short-wavelength system. In addition to this, we wanted to compare SWS and
achromatic resolution acuity at different retinal locations of equal
eccentricity. SWS and achromatic grating resolution acuity was measured in
two observers at a number of different retinal meridians of 10- and 25-deg
eccentricity from the fovea, and out to 35-deg eccentricity along the
horizontal meridian. Achromatic resolution acuity was higher than SWS
resolution acuity at all locations. At 10-deg eccentricity there was
slight radial asymmetry in SWS and achromatic acuity, both displaying
highest acuity along the horizontal meridian. At 25-deg eccentricity, SWS
and achromatic acuity showed significant asymmetry with acuity being
higher in the nasal retina compared to the temporal retina and with higher
acuity in the superior retina compared to the inferior retina. At 35-deg
eccentricity, the acuity asymmetry along the horizontal meridian was
maintained with acuity for both significantly higher in the nasal retina.
The SWS acuity changes with eccentricity and meridian were qualitatively
similar to that found for achromatic acuity at the majority of retinal
locations. Like achromatic acuity, SWS acuity shows significant asymmetry
at different retinal locations of equal eccentricity. This suggests that
both the midget and small bistratified ganglion cell population density
changes significantly with retinal location and eccentricity. SWS acuity
appears to change in parallel with achromatic acuity for the majority of
retinal locations measured, although the amount of nasotemporal asymmetry
appears to be slightly less for the SWS system at 25- and 35-deg
eccentricity.