Review Highlights Role of OCT-A in Neurodegenerative Diseases

Although optical coherence tomography angiography (OCT-A) is an effective tool for understanding a number of retinal pathologies like diabetic retinopathy and age-related macular degeneration, the technology has recently been used to evaluate abnormalities presenting in several neurodegenerative disorders, including multiple sclerosis, Alzheimer’s disease, and Parkinson disease.

According to a review published in Eye and Brain, the use of OCT-A, a noninvasive imaging technique for analyzing the retinal and choroidal microvasculature in vivo, can play a pivotal role in the detection and monitoring of these disorders.

“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),” researchers wrote. “It therefore provides unique insight into the exact retinal or choroidal layer and location at which abnormal blood flow develops.”

In order to summarize published findings on the use of OCT-A in neuro-ophthalmology and neurology, and to elucidate on the basic principles and algorithms of OCT-A, investigators searched Google Scholar, PubMed, and Mendeley databases for relative literature on the subject.

A total of around 130 published manuscripts were included in the review. The majority of included studies were published in 2015 or afterwards as OCT-A was approved by the FDA in 2015.

Researchers found several OCT-A devices use different algorithms including ultrahigh-sensitive optical microangiography, split-spectrum amplitude decorrelation angiography, and full-spectrum amplitude decorrelation algorithm.

In addition, use of OCT-A in healthy individuals has been valuable in that the images provide a reference of normal vasculature, thus aiding in the identification of abnormalities. “OCT-A in otherwise normal controls reveals an even blood flow in both the deep and superficial vascular plexuses and clear visualization of the retinal and choroidal layers,” authors wrote.

When it comes to OCT-A use in neurovegetative diseases, researchers found:

• In multiple sclerosis, OCT-A findings include significant reduction of the blood flow within the parafoveal region and the optic nerve head
• It has been postulated that the changes of the retinal vasculature in Alzheimer’s patients could serve as a biomarker for the severity and progression of the disease, and OCT-A demonstrates diminished blood flow that will eventually lead to thinning and death of retinal cells
• OCT has been used to study the changes in the retinal layers and optic nerve in Parkinson disease and its variants, Progressive Supranuclear Palsy and Multiple System Atrophy
• In individuals with Wolfram Syndrome, OCT-A demonstrated reduced blood flow of the radial peripapillary capillary plexus and superficial capillary plexus, which correlated well with the corresponding retinal nerve fiber layer thinning

However, because OCT-A was only approved in 2015, many of the studies included in the review contain small sample sizes, limiting the level of evidence and the validity of findings.

“There is still a significant learning curve in terms of interpretation [of OCT-A findings] and there is no unanimous protocol as to which parameters should be taken into account,” authors wrote. “This may lead to false-positive or -negative results that affect the validity of the findings and yield contradictory results among different study groups.”

Commercially available OCT-A devices are also limited in that they do not provide a wide field of view of the vasculature of the peripheral retina, meaning views are limited to the posterior pole. To optimize the quality of OCT-A images and accurate interpretation of data, larger prospective longitudinal studies ought to be carried out.

“OCT-A can provide valuable data about the structural changes of the retinal and optic nerve vascular network and this can be used for the development of biomarkers to monitor the disease progression and also to develop potential future treatments which could halt or reverse the progression of such diseases that are currently incurable,” authors concluded.

Reference

Tsokolas G, Tsaousis KT, Diakonis VF, et al. Optical coherence tomography angiography in neurodegenerative diseases: a review. Eye Brain. Published online July 14, 2020. doi:10.2147/EB.S193026