OCT-defined optic atrophy thresholds are associated with blunted optic nerve swelling in recurrent optic neuritis

Acute optic neuritis (ON) can be associated with optic disc edema which can be quantified by optical coherence tomography (OCT) peripapillary retinal nerve fiber layer (RNFL) measurements. In patients with recurrent visual symptoms, objective measures can confirm a new clinical attack. Optic atrophy may preclude RNFL swelling during recurrent ON, but this has not been systematically evaluated.

Patients with recurrent ipsilateral ON with OCT within 2 weeks of symptoms were retrospectively identified from 8 international centers.

We identified 112 patients (MOGAD, 45[40%]; MS, 36[32%], NMOSD, 20[18%], idiopathic ON, 11[10%]) with 137 episodes of recurrent ON (median age, 39 years [range 12-78]; female sex, 81 [72%]). Of patients with macular ganglion cell-inner plexiform layer (GCIPL) measures during acute recurrent ON, those with preserved GCIPL (≥65 μm, n=36) showed greater RNFL thickness (mean 108 μm [65-368], p<0.0001) than those with thin GCIPL (<65μm, n=30; mean 65μm [50-84]). Higher RNFL thickness measurements, which can be consistent with RNFL swelling, (≥15 µm above GCIPL) occurred in 21/36 (58%) patients with GCIPL ≥65 µm vs 5/30 (17%) patients with GCIPL <65µm (p<0.001).

Patients with severe optic atrophy may have limited optic nerve swelling during acute ON. Ganglion cell layer thickness can serve as a surrogate marker for optic atrophy during early acute ON. We identified quantitative thresholds (GCIPL [<65μm] or prior RNFL [<70μm]) at which optic nerve swelling is unlikely to occur during recurrent acute ON. This is important for objective assessment of ON in clinical practice and clinical trials.