Loss of P retinal ganglion cell function in resolved optic neuritis

To determine the relative loss of P and M (X and Y) ganglion cell function in unilateral resolved optic neuritis, 10 patients with 20/20 or better Snellen acuity in both eyes had contrast sensitivity testing, color vision testing, and automated perimetry. We used contrast sensitivity gratings of 0.5 cycles per degree (cpd) with a rate of counterphase temporal modulation of 30 Hz and gratings of 11.4 cpd at 1 Hz. On 1 trial, patients responded when they detected the pattern of the grating and on the next trial when they 1st perceived movement. There was a significant difference in the 1 Hz high spatial frequency pattern and movement results suggesting loss of P cell function. Two patients were unable to perceive any movement with their involved eye with this target, but could detect the pattern. There was no significant difference between the involved and uninvolved eyes in the low spatial frequency pattern detection values. This is a function ascribed to the M cell. There was also loss of low spatial frequency movement detection. Although there was significant depression of the entire visual field in the involved eye, the probability plots showed the most significant loss in the cecocentral area. Farnsworth-Munsell 100 Hue color testing was also abnormal. Greater involvement of P than M ganglion cell axons may explain these contrast sensitivity abnormalities, central scotomata, and color vision loss.