Commentary: Applicability of optical coherence tomography angiography for imaging ocular biomarkers of systemic diseases.

Optical coherence tomography angiography (OCTA) is a relatively new imaging modality that is primarily used to assess the microvascular network of the retina, choroid, and optic disc.[1] It allows for a dyeless and non-invasive evaluation of the vasculature in a variety of chorioretinal vascular disorders.[1] Researchers can use OCTA to look at quantitative factors such as the foveal avascular zone (FAZ) area, superficial capillary plexus vessel density (SCP VD), deep capillary plexus vessel density (DCP VD), vascular length density (VLD), and acircularity index (AI).[1] Given its non-invasive nature and ability to create high-quality reproducible images, this imaging technique is gaining appeal among Vitreoretinal Specialists.

The retina is an incredibly easy and accessible organ to image the internal structure of the human body because of the architecture of the eye.[2] The condition of the vasculature throughout the body is presumed to be comparable to that of the retinal blood vessels.[2] As a result, the status of systemic disease can be monitored based on retinal blood vessel examination.[2] This is especially true in neurological disorders since the vascular architecture of the brain and retina twin to a great extent.[3] The extent of OCTA abnormalities has been shown to correlate with the severity of various neurodegenerative and neurovascular diseases, such as Alzheimer’s disease, multiple sclerosis (MS), Parkinson’s disease, migraines, papilledema, arteritic and non-arteritic optic neuropathy (AION and NAION), Leber’s hereditary optic neuropathy (LHON), amyotrophic lateral sclerosis (ALS), Huntington’s disease, and so on.[3]

The role of OCTA is slowly evolving in other fields such as cardiology, pulmonology, nephrology, and diabetology.[234567] Amongst them, diabetic and hypertensive patients have been extensively studied with OCTA. Using OCTA, Diabetics without diabetic retinopathy (DR) were found to have decreased superficial and deep retinal VD with increased areas of FAZ and nonperfusion when compared to healthy participants.[8] Furthermore, OCTA evaluation can be used to predict an elevated risk of developing diabetic macular edema (DME) and DR progression.[4] A similar reduction in the VD and FAZ enlargement has also been demonstrated in hypertensive patients.[7] Indeed, Lee et al.[2] demonstrated comparable alterations on OCTA in patients with chronic hypertension who had and did not have clinical abnormalities of hypertensive retinopathy (HTR), emphasizing the importance and sensitivity of this imaging modality. In some pulmonological disorders, retinal vascular changes may occur as a result of secondary changes caused by systemic inflammation and hypoxia rather than as a direct result of the original microvascular pathology.[6] In their study on evaluation of retinal and optic disc microvascular changes in patients with stable chronic obstructive pulmonary disease (COPD), Kurtul et al.[6] showed the severity of COPD to have a negative impact on OCTA parameters, including the VD in the superficial and deep retinal plexuses. Although the study is limited by a small sample size, the results presented are very interesting, and further studies with a larger sample size and longer follow-up are needed to validate the results and further explore this relationship.[6]

Thus, it can be observed that OCTA provides a considerable amount of valuable information about the vascular status of the retina and throughout the body. Since OCTA is a highly sensitive imaging modality, it can detect subtle changes in vascular perfusion quite early.[1] These changes can be a surrogate biomarker in early systemic disease, especially in neurological conditions. Investigating the chronology of vascular alterations on OCTA in relation to structural changes could help answer fundamental questions about disease causation. Presently, numerous systemic disorders are being investigated by OCTA for their potential role in diagnosis and monitoring the therapeutic response.[2345678] Thus, the micromorphometry of the retinal, choroidal, and optic disc vasculature, as demarcated and quantified by the OCTA, may be a valuable biomarker for the management and prognosis of diseases, not only in the field of ophthalmology but also in other branches of medicine.