38 — Optical Coherence Tomography (OCT) in Optic Neuritis and Multiple Sclerosis

This review discusses optical-coherence tomography (OCT) and its usefulness in diagnosis of diseases including multiple sclerosis (MS) and optic neuritis (ON).

It first reviews retinal nerve fiber (RNFL) thinning in MS patients versus healthy patients. This study (Parisi et al, 1999) also explores the impact of ON on RNFL thickness. Another study (Pro et al, 2006) finds that early optic neuritis can sometimes result in a pardoxical thickening of the retina, likely caused by edema (the study didn’t find signs of other types of swelling). Along with Noval et al (also 2006), these studies demonstrated the importance of knowing the elapsed time since ON onset: Early ON may show signs of thickening which could confound the thinning results seen in MS.

Under 70μm RNFL thickness, Costello et al (2006) discovered that vision-loss correlated with thinning of the retina, which was substantiated by other more recent studies. At this level of vision loss, it becomes unlikely that surgical intervention would return visual acuity fully.

Recently, OCT has been used as a proxy for axonal loss in the brain of MS patients (I talk more about this at length in this post). However, it is still unclear whether the lesioning responsible for the thinning of retina is occurring in optic nerve (leading to Wallerian degeneration) or in the retinal disc itself.

The relationship between retinal thinning (as read by OCT) and MS/ON comorbidity is complicated as has some very significant implications in a clinical setting: If ON progression cannot be accurately followed, ON+MS patients’ RNFL thinning cannot be appropriately measured, because the ON may be contributing to thinning or thickening, depending on stage.

This means that prognosis is highly reliant on high-quality and time-sensitive scans with some degree of regularity, which probably comes as a surprise to no one.