RNFL thickness in MS-associated acute optic neuritis using SD-OCT: critical interpretation and limitations

Abstract

Axonal loss is considered a key prognostic factor in diagnosing and monitoring the progress of multiple sclerosis (MS). The purpose of our research was to determine whether the measurement of retinal nerve fibre layer thickness (RNFLT) as measured with high-resolution spectral-domain optical coherence tomography (SD-OCT) differs between optic nerve injury following acute optic neuritis (ON) or following unregistered subclinical axonal damage in patients with MS. High-resolution SD-OCT measurements of RNFLT were initially carried out in the acute phase of ON and again after 3 months, in 25 patients with clinical definite MS and 25 sex- and age-matched healthy controls, all at the University Eye Hospital, Vienna. Conventional OCT-based RNFLT analysis correctly identified all three patients with initial RNFL swelling. However, only two of three acute ON eyes with a history of ON were registered with RNFLT decrease in seven peripapillary sectors (PPs). The remaining have only been revealed using RNFLT symmetry comparison. Two of 22 (9%) first-episode ON eyes were labelled as pathologic. The number and metric RNFL values of pathologically labelled PPs remained unchanged after 3 months. Our age- and sex-match-based measurement model, with patients with MS being plotted individually and towards the fellow eye, identified all acute ON eyes (with a history of prior ON) with RNFLT reduction in 11 PPs. A global RNFL loss was registered in 36.4% (eight of 22 eyes). However, in 72%, or 16 of 22 ON eyes presenting with first episode of acute ON, a segmental RNFL loss was initially registered in 39 PPs upon baseline examination. The number of PPs with identified axonal decrease increased to a total of 48 PPs within the observational period. Spectral-domain optical coherence tomography imaging of identical scanning locations, combined with an optimized scan centring around the optic disc, offers the technological potential of detecting prior, subtle, clinically unregistered optic nerve injury within MS individuals. Significant discrepancy in RNFLT to the potential ON eye may be achieved by comparing OCT metrics with the fellow eye and a sufficient number of age and sex-matched controls.