Are high-pass resolution perimetry thresholds sampling limited or optically limited?

Abstract

It has been reported that high-pass resolution perimetry (HRP) provides a means of noninvasively determining retinal ganglion cell density. However, there is evidence to suggest that this may not be true. The purpose of the present study was to determine whether HRP thresholds are sampling limited, which is a necessary condition for being able to determine retinal ganglion cell density psychophysically. This study measured resolution and detection performance for a range of grating-based stimuli under the testing conditions that HRP uses and compared these with performance of the ring stimulus. The results show that detection and resolution acuity under HRP test conditions were often equivalent, in accordance with previous investigations. However, the results also show that the thresholds underestimated the true level of resolution acuity in the periphery because increasing stimulus contrast increased performance. These findings suggest that HRP thresholds cannot be regarded as sampling limited, but rather they are optically limited. We therefore conclude that HRP thresholds cannot be regarded as a direct measure of the underlying ganglion cell density.