The application of optical coherence tomography in neurologic diseases

Abstract

Optical coherence tomography (OCT) has become an increasingly popular tool in various disciplines of medicine, particularly ophthalmology and neurology. It is an imaging technology that has revolutionized the practice of ophthalmology by providing anatomic detail of pathologic changes in the retina and optic nerve. OCT is routinely used as an ancillary test that can aid in the diagnosis and monitoring of neuro-ophthalmic diseases such as papilledema, optic neuritis, and neuroretinitis. OCT measurements have also been shown to predict visual prognosis in compressive optic neuropathies. Changes in OCT measurements have been used to study the course of particular neurologic diseases such as multiple sclerosis, suggesting that the data obtained may be useful as a biomarker in diagnosing and treating neurodegenerative disease. We present an up-to-date review of the OCT findings in several diseases of neurologic interest and provide clinical examples pertinent to the general neurologist.

Retinal layer segmentation Figure 1. Images shown were obtained with Spectralis spectral-domain optical coherence tomography (SD-OCT) system (Heidelberg Engineering, Germany). Top panel is a cross-sectional SD-OCT scan at the fovea that shows all the retinal layers segmented. The most relevant to study neurologic diseases are labeled. From top to bottom, the segmented retinal layers are as follows: internal limiting membrane, nerve fiber layer, ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, external limiting membrane, myoid zone, ellipsoid zone, retinal pigment epithelium, Bruch membrane complex. Bottom panels depict the segmented layer with the corresponding color thickness map plotted below.

Early and late optical coherence tomography features in optic neuritis Figure 2. Top row: on the day of symptoms presentation with vision of 20/40. Bottom row: 4 months later with vision of hand motion. (A) System automatic segmentation, thinner in the late stage. (B) Retinal nerve fiber layer (RNFL) thickness profile compared against normative data. (C) RNFL thickness per quadrants in a circle around the optic nerve (peripapillary thickness). (D) Total retinal thickness maps that includes RNFL and ganglion cell layer. INF = inferior; N = nasal; NAS = nasal; NI = nasal-inferior; NS = nasal-superior; SUP = superior; T = temporal; TMP = temporal; TI = temporal-inferior; TS = temporal-superior.

Papilledema severity as seen by confocal scanning laser ophthalmoscopy (SLO) Figure 3. This feature, available on the Spectralis optical coherence tomography (OCT) system, utilizes a laser light to scan the retina point by point. The light reflected from the retina goes through a small aperture, which eliminates light coming from other panes, resulting in a sharp, high-resolution image. We present SLO scans corresponding to the clinical stages of the Frisen scale. Note that the scan of grade 5 could not be reliably created due to the amount of nerve swelling that goes beyond the imaging window on OCT.