Abstract
Purpose :
To assess residual retinal ganglion cell (RGC) function in patients with recovered optic neuritis and history of multiple sclerosis (MS).
Methods :
Subjects were normal controls (NC, n = 32, age: 42 ± 12.7 years) and MS patients (n= 17, age: 43 ± 9.4 years) with past history of unilateral optic neuritis (ON). Visual acuity (20/20) and color vision (Ishihara) were normal in both ON eyes and fellow eyes (FE). RNFL thickness was reduced in ON (81.9 ±10.9 µm) and FE (92.2 ± 12.0 µm) compared to NC (99.1 ±8.9 µm). RGC function was simultaneously assessed from each eye with Pattern Electroretinogram (PERG) in response to horizontal gratings (1.6 cycles/deg, 15.63 reversals/s, 98% contrast, 800 cd/sqm mean luminance, 25 deg field) generated on a LED display (Jorvec). Averaged PERG signals (1,024 epochs) were Fourier analyzed to retrieve amplitude (nV) and phase (deg) converted in latency (ms).
Results :
While PERG amplitude was not significantly (P=0.42) different between NC, ON and FE eyes, the PERG latency was significantly shorter in ON (49.8 ± 3.9 ms, P=0.0026) and FE (50.6 ± 3.0 ms, P=0.027) than in NC (52.9 ± 2.5 ms). PERG latencies did not differ between ON and FE (P=0.45) and were not significantly correlated with RNFL thickness (ON, P=0.09; FE, P=0.22). As small diameter axons may be preferentially involved in MS, we simulated pathological PERG changes in control subjects (n=8) by artificially reducing the relative contribution of smaller diameter axons to the PERG response. To do so, the visual stimulus was blurred with positive lenses to Jaeger Visual Acuity = J5, which selectively impaired vision of high spatial frequencies. The blurred PERG latency (49.0 ± 2.2 ms) was shorter (P=0.013) than baseline (51.9 ± 2.1 ms).
Conclusions :
Recovered ON eyes have abnormal RGC function. Abnormally short PERG latency in ON eyes is consistent with the notion that smaller diameter, slower axons (parvocellular RGCs) are preferentially affected in MS, the residual response being dominated by RGC axons with faster dynamics (magnocellular RGCs). Abnormal PERG latency in FE suggests subclinical dysfunction of the parvocellular pathway. Assessment of PERG in MS and ON may help identify and monitor patients early in the course of the disease.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.