Optical Coherence Tomography (OCT): Imaging the Visual Pathway as a Model for Neurodegeneration

Abstract

Summary: Axonal and neuronal degeneration are important features of multiple sclerosis (MS) and other neurologic disorders that affect the anterior visual pathway. Optical coherence tomography (OCT) is a non-invasive technique that allows imaging of the retinal nerve fiber layer (RNFL), a structure which is principally composed of ganglion cell axons that form the optic nerves, chiasm, and optic tracts. Since retinal axons are nonmyelinated until they penetrate the lamina cribrosa, the RNFL is an ideal structure (no other central nervous system tract has this unique arrangement) for visualizing the processes of neurodegeneration, neuroprotection and, potentially, even neuro-repair. OCT is capable of providing high-resolution reconstructions of retinal anatomy in a rapid and reproducible fashion and permits objective analysis of the RNFL (axons) as well as ganglion cells and other neurons in the macula. In a systematic OCT examination of multiple sclerosis (MS) patients, RNFL thickness and macular volumes are reduced when compared to disease-free controls.Conspicuously, these changes, which signify disorganization of retinal structural architecture, occur over time even in the absence of a history of acute demyelinating optic neuritis. RNFL axonal loss in MS is most severe in those eyes with a corresponding reduction in low-contrast letter acuity (a sensitive vision test involving the perception of gray letters on a white background) and in those patients who exhibit the greatest magnitude of brain atrophy, as measured by validated magnetic resonance imaging techniques. These unique structure-function correlations make the anterior visual pathway an ideal model for investigating the effects of standard and novel therapies that target axonal and neuronal degeneration. We provide an overview of the physics of OCT, its unique properties as a non-invasive imaging technique, and its potential applications toward understanding mechanisms of brain tissue injury in MS, other optic neuropathies, and neurologic disorders.

Optical Coherence Tomography in Patients with Relapsing-Remitting Multiple Sclerosis without Optic Neuritis: A 20-Month Longitudinal Study

“…2 Retinal cell axons are part of the CNS, and do not have a myelin sheath until they penetrate the lamina cribrosa, thus the investigation of retina might be ideal for visualising the processes of neuroaxonal degeneration and understanding mechanisms of brain tissue damage in multiple sclerosis. 5 One of the relatively novel techniques for investigation of retina is optical coherence tomography (OCT). OCT is a non-invasive technique that allows direct visualization and measurement of retinal nerve fibre layer (RNFL) thickness, macular volume, and optic disc parameters with micron-scale resolution.…”

Optic Atrophy in End-Stage Giant Axonal Neuropathy: A Case Report

“…OCT is particularly promising in assessing axonal preservation in multiple sclerosis and is currently being investigated as a structural outcome measure in neuroprotection trials. [25][26][27] With baseline measurements acquired, serial OCT of RNFL may also offer a non-invasive means of monitoring progression in GAN for future therapeutic studies. …”

Corticosteroids and Anti-Complement Therapy in Retinal Diseases

“…Spontaneous improvement to Snellen visual acuity >20/40 occurs in more than 90% of eyes. However deficits in contrast sensitivity may be permanent, and thinning of the nerve fiber layer is typically observed by optical coherence tomography (OCT) Galetta et al 2011;Lamirel et al 2010;Sakai et al 2011). We now understand that for future pharmacologic studies to detect benefits in treatment of optic neuritis, additional studies are required; retinal ganglion cell loss may be better investigated using new or improved techniques including OCT and scanning laser polarimetry (SLP) to evaluate the nerve fiber layer or the thickness of the ganglion cell layer and inner plexiform layers (GCL+IPL) .…”