Retinal ganglion cell function in recovered optic neuritis: Faster is not better

Objective: To assess residual retinal ganglion cell (RGC) function in patients with recovered optic neuritis (ON) and multiple sclerosis (MS). Methods: Age-matched controls (C, n = 32) and MS patients (n = 17) with history of ON in one eye but normal visual acuity and color vision were tested with steady-state Pattern Electroretinogram (PERG). Light Emitting Diodes (LED)-generated bar gratings, robust signal averaging and Fourier analysis were used to assess response amplitude and latency. Results: PERG amplitude was similar for C, ON and fellow eyes (FE) (P = 0.4), but PERG latency was shortened in ON by 3.2 ms (P = 0.002) and in FE by 2.0 ms (P = 0.02) and was correlated (P < 0.01) with both Retinal Nerve Fiber Layer (RNFL) and Ganglion Cell Inner Plexiform Layer (GCIPL) thicknesses. PERG latency shortening could be simulated in control subjects (n = 8) by dioptrically blurring the edges of gratings (high spatial frequencies), which reduced activity of parvocellular RGCs with smaller/slower axons. The blurred PERG latency was shorter than baseline by 2.9 ms (P = 0.01). Conclusions: PERG latency is shortened in both eyes of MS patients with recovered unilateral ON, suggesting relative dysfunction of RGCs with slower axons and sparing of RGCs with faster axons. Significance: Assessment of PERG latency in MS and ON may help identifying and monitoring RGC dysfunction. PERG latency shortening in FE suggests primary retinopathy in MS.