Optical Coherence Tomography Angiography in Neurodegenerative Diseases: A Review

Abstract

Background: Optical coherence tomography angiography (OCT-A) has emerged as a novel, fast, safe and non-invasive imaging technique of analyzing the retinal and choroidal microvasculature in vivo. OCT-A captures multiple sequential B-scans performed repeatedly over a specific retinal area at high speed, thus enabling the composition of a vascular map with areas of contrast change (high flow zones) and areas of steady contrast (slow or no flow zones). It therefore provides unique insight into the exact retinal or choroidal layer and location at which abnormal blood flow develops. OCTA has evolved into a useful tool for understanding a number of retinal pathologies such as diabetic retinopathy, age-related macular degeneration, central serous chorioretinopathy, vascular occlusions, macular telangiectasia and choroidal neovascular membranes of other causes. OCT-A technology is also increasingly being used in the evaluation of optic disc perfusion and has been suggested as a valuable tool in the early detection of glaucomatous damage and monitoring progression.

Objective: To review the existing literature on the applications of optical coherence tomography angiography in neurodegenerative diseases.

Summary: A meticulous literature was performed until the present day. Google Scholar, PubMed, Mendeley search engines were used for this purpose. We used 123 published manuscripts as our references. OCT-A has been utilized so far to describe abnormalities in multiple sclerosis (MS), Alzheimer's disease, arteritic and non-arteritic optic neuropathy (AION and NAION), Leber's hereditary optic neuropathy (LHON) papilloedema, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis (ALS), Wolfram syndrome, migraines, lesions of the visual pathway and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). It appears that OCT-A findings correlate quite well with the severity of the aforementioned diseases. However, OCT-A has its own limitations, namely its lack of wide-field view of the peripheral retina and the inaccurate interpretation due to motion artifacts in uncooperative groups of patients (e.g. children). Larger prospective longitudinal studies will need to be conducted in order to eliminate the aforementioned limitations.

Keywords: neuro-ophthalmology; neurodegenerative diseases; optical coherence tomography angiography.

Figure 1

Left Side: Disc OCT-A of a healthy control subject. Right side: Disc OCT-A of an optic neuritis disc showing reduced density of the optic nerve head blood vessel network. This implies reduced blood flow on the optic nerve head. Notes: Red solid lines indicate the ONH area that was used for the relevant flow index calculations. Copyright © 2014. BMJ Publishing Group Limited. Modified from Wang X, Jia Y, Spain R, et al. Optical coherence tomography angiography of optic nerve head and parafovea in multiple sclerosis. Br J Ophthalmol. 2014;98:1368–1373.

Figure 2

Upper left and lower left images demonstrate the appearance of a healthy optic disc. Upper right and lower right images demonstrate the attenuation and peripapillary capillary drop out of the optic nerve head vascular network in a patient with NAION. Note: Copyright © 2017. International Journal of Ophthalmology. Modified from Ling JW, Yin X, Lu QY, Chen YY, Lu PR. Optical coherence tomography angiography of optic disc perfusion in non-arteritic anterior ischemic optic neuropathy. Int J Ophthalmol. 2017;10:1402–1406.

Figure 3

OCT-A images of a patient with Leber hereditary optic neuropathy. Notes: (A–C) Peripapillary capillary telangiectatic vessels in the deep plexus shown with black arrows. (B–D) Peripapillary capillary telangiectatic vessels in the outer retina shown by black arrows. © 2016 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd. Modified from Takayama K, Ito Y, Kaneko H, Kataoka K, Ra E, Terasaki H. Optical coherence tomography angiography in leber hereditary optic neuropathy. Acta Ophthalmol. 2016;95(4):e344-e345.