<p>Optical Coherence Tomography Angiography in Neurodegenerative Diseases: A Review</p>

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.

Retinal Microvasculature in Schizophrenia

“…7 Studies of changes in neural retinal structure have been informative regarding changes in brain structure and function, and disease progression, in neurodegenerative diseases, 7 and accumulating evidence suggests that retinal microvasculature changes are also informative in cases of CNS disease. 3,[8][9][10][11] A brief and non-invasive method for assessing the state of retinal vasculature is optical coherence tomography angiography (OCTA). [12][13][14][15][16][17][18] OCT is a method based on lowcoherence interferometry that uses the difference between the power in spectral frequencies of near-infrared light reflected back from the eye, relative to the frequency composition of the original light output, to generate detailed images of retinal layers (conventional OCT) and the retinal microvasculature (OCTA), in a manner analogous to how ultrasound is used to generate biological images.…”

Cerebral Modifications in Glaucoma and Macular Degeneration: Analysis of Current Evidence in Literature and Their Implications on Therapeutic Perspectives

“…15 Even more interesting are the results obtained through OCTangiography (OCT-A), which allows the evaluation of the retinal blood vessels: the retinal vascular network has many similarities with the cerebral vasculature, potentially reflecting the modifications occurring in some neurodegenerative diseases such as AD. 9,16 In glaucoma, the existence of an unstable ocular perfusion has been previously demonstrated in the optic nerve, retina, and extraocular level, 17 either due to IOP fluctuation or to a to primary vascular dysregulation, which is responsible for both ischemic damage and subsequent reperfusion injury to the ganglion cells: 18 moreover, using OCT-A it was possible to observe an effective reduction of macular microvascular flow, particularly in the superficial retinal plexus. [19][20][21] This flow disturbance would lead to a reduction in the thickness of GCC and RNFL, anatomically more susceptible to this impairment, showing an association between visual field defect, flow reduction and thinning of the layer.…”

“… 22 Interestingly, a reduction in macular flow has also been observed in AD, but this time involving both the superficial and deep retinal plexus. 16 , 23 , 24 It has been hypothesized this alteration could be produced by intraretinal deposition of β-amyloid, which has been identified in AD patients, causing both a mechanical compression on capillaries and a physical obstacle to the diffusion of oxygen and nutrients: 16 this would result in a metabolic distress to ganglion cells and a subsequent degeneration and thinning of the GCC, which correlates with the disease severity. 16 To date, the main therapeutic strategy for glaucoma is lowering IOP through the use of hypotonic drugs or surgery.…”

Optical Coherence Tomography Angiography (OCTA) in Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorder

“…This provides some evidence for possible vascular regeneration or increase of lumen thickness in chronic disease, but additional longitudinal data on the microvasculature in MS, including in its earlier stages, are needed to interpret these findings. Future longitudinal data are required to identify if OCTA can function as a biomarker to predict and monitor disease progression in MS and other neurodegenerative disease ( 66 ).…”