An intereye difference of 5-6 μm in retinal nerve fiber layer (RNFL) thickness is a robust structural threshold for identifying the presence of a unilateral optic nerve lesion in multiple sclerosis (MS), a recent study found. Researchers analyzed spectral domain optical coherence tomography (OCT) data of 31 healthy volunteers and 124 patients with MS at a single center as part of an ongoing collaborative investigation of visual outcomes. They found:

• Among healthy volunteer participants (n=31), the 95th percentile value for intereye difference (upper boundary of expected for normal controls) was 6.0 μm.
• This value was applied to the convenience sample group of MS patients.
• Positive predictive value, negative predictive value, sensitivity, and specificity for identifying MS patients with a history of unilateral optic neuritis (ON) were calculated for the 6-μm threshold value in a 2 × 2 table analysis with the application of χ² tests.
• The 6-μm threshold was predictive of worse binocular low-contrast acuity scores at 2.5% and 1.25%.
• A receiver operating characteristic curve analysis demonstrated an optimal intereye difference threshold of 5 μm for identifying unilateral ON in the MS cohort.