Optic neuritis is a common presentation of MS. Acute inflammation of the optic nerve can lead to transient swelling of the peripapillary retinal nerve fiber layer (pRNFL). Further injury of axons within the optic nerve may lead to degeneration of the retinal ganglion cell (RGC) layer within the macula. RGC layer thickness has been proposed as a measure of neurodegeneration because it is relatively resistant to confounding inflammation. A study was done to track the changes in the retinal layer during a 6-month period in 27 patients with acute optic neuritis to identify patterns of RGC layer changes.
At baseline, optic neuritis eyes had no difference in RGC layer thickness but had increased thickness of pRNFLs compared with unaffected eyes. By 6 months, pRNFL in affected eyes was decreased by 20.9 µm (21%) compared with unaffected eyes, and RGC was reduced by 11.3 µm (16%). For pRNFL, swelling was largely resolved by 1 month; atrophy was most rapid between months 1 and 2. For the RGC layer, atrophy occurred primarily from baseline to month 1. A decrease in RGC layer by ≥4.5 µm at 1 month predicted poor recovery of contrast sensitivity.
Optical coherence tomography (OCT) is now commonly used in MS centers to monitor disease course and track potential adverse events (e.g., macular edema with fingolimod). OCT also provides important outcome measurement in MS clinical trials. The ganglion cell layer can be segmented and may provide information about neurodegeneration within the visual system. This analysis demonstrates that in acute optic neuritis, greater loss of ganglion cell layer predicts worse clinical outcome. In the future, such tools may help to stratify risk and identify patients who need closer monitoring. The ganglion cell layer thickness measurement will also help evaluate neuroprotective and remyelination effect in upcoming MS trials.
