Can Optical Coherence Tomography Be Used to Guide Treatment Decisions in Adult or Pediatric Multiple Sclerosis?

Jeffrey Lambe, Olwen C. Murphy, Shiv Saidha

With the recognition that neurodegeneration represents the principal substrate of disability in multiple sclerosis (MS), there has been increased strives towards identifying biomarkers for accurately quantifying and tracking neurodegeneration during the disease course. The retina provides an opportune "window" into the central nervous system (CNS) in MS, with retinal changes in MS reflecting not only local, but also global aspects of neurodegeneration and inflammation operative in the disease. Optical coherence tomography (OCT) is a rapid, inexpensive, reproducible, high-resolution imaging technique allowing accurate quantification of discrete retinal layers. OCT determined thinning of inner retinal layers such as the retinal nerve fiber layer (RNFL) and in particular the composite of the ganglion cell and inner plexiform (GCIP) layers, predominantly related to optic neuropathy, have been shown to not only correlate with high and low contrast visual function in MS, but also global MS disability scores, as well as whole brain and particularly gray matter volumes. Rates of GCIP thinning have been shown to be accelerated among MS patients exhibiting inflammatory activity outside of the visual pathways, as well as disability progression during follow-up. Moreover, baseline RNFL thickness in MS has been shown to have utility for predicting future disability accumulation. On the other hand, thickening of the inner nuclear layer (INL) in MS, the pathophysiologic basis of which remains to be elucidated, has been found to predict the development of clinical and radiological inflammatory activity, as well as subsequent disability progression in MS. Given the potential for OCT to provide insight into neurodegeneration and inflammation occurring in MS, this review focuses on the potential utility of OCT within the clinical setting to influence treatment decisions for MS patients. The evolution of spectral domain-OCT technology, with improved resolution and reproducibility allowing intra-retinal layer segmentation, has facilitated the determination that the OCT derived measure GCIP thickness is a highly accurate measure for quantifying and tracking neurodegeneration, and conversely neuroprotection, in MS. The strong relationships between rates of GCIP and brain atrophy across MS subtypes over time underpin the insight derived regarding the global MS disease process from OCT and highlight OCT as an excellent complementary tool to magnetic resonance imaging (MRI) for tracking MS patients. More recently, longitudinal studies are emerging which support the utility of OCT for monitoring the differential effects of disease-modifying therapies (DMTs) in MS. Although further work is required, there is mounting evidence supporting the utility of OCT in the clinical setting to monitor disease course in individual patients with MS and to aid in the prediction of disease course. As pharmacological treatment options in MS expand to also include potentially neuroprotective and/or remyelinating or neurorestorative drugs, OCT as a biomarker of neurodegeneration and neuroprotection (and neuroinflammation to a lesser degree) may become an invaluable tool in both the research and clinical settings.