Commentary: Macular vessel densities in non-invasive optical coherence tomography angiography: Challenges in intermediate uveitis : Indian Journal of Ophthalmology

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Commentary: Macular vessel densities in non-invasive optical coherence tomography angiography: Challenges in intermediate uveitis

Das, Dipankar; Bhattacharjee, Harsha; Mishra, Sakshi; Mahapatra, Madhusmita

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Indian Journal of Ophthalmology 71(1):p 160-161, January 2023. | DOI: 10.4103/ijo.IJO_2243_22

Dyeless, non-invasive optical coherence tomography angiography (OCT-A) is an easy, fast, software-generated newer investigative tool for retinal and uveitic diseases.[12345] In the past few years, the structural and functional components of retinal diseases were studied by OCT-A with revolutionary development.[12345] OCT-A stressed an understanding of histology and histopathology of retinal and choroidal layers.[12345] Retinal vessel density mapping particularly in the macula is the proportion of blood vessel areas with blood flow measured over the total area.[12345]

The macula in the posterior pole has a thickness of 160–190 μm where it forms a slight depression having the fovea and within it, the foveola.[12345] The fovea has the highest concentration of cones with a high density of xanthophyllic pigments and pigment epithelial cells which are densely filled and have a high density of pigment granules.[12345] OCT-A can involve split-spectrum amplitude-decorrelation angiography which helps in the clear differentiation of superficial and deep vascular plexuses.[12345] The superficial vascular plexus is located in the ganglion cell layer and nerve fiber layer, whereas the deep vascular plexus is located in the inner nuclear and external plexiform layers.[12345] The superficial plexus has vascular distribution represented by white linear structures against the black background in centripetal arrangement forming a web by secondary retinal vessels.[123456] The deep plexus consists of a close interlaced pattern around the avascular foveal zone. Both superficial and deep vascular plexuses are interconnected with small vessel anastomoses.[12345]

The present article by the author(s)[1] to document macular vessel densities by OCT-A is a step forward in intermediate uveitis (IU) among South Indian uveitic populations.[1] The correlation of this study with the baseline normative OCT-A data is important.[1] IU is fairly common in uveitis patients in almost all patterns of uveitis studies within India and abroad.[17] There may be various causes of IU which include both infectious and noninfectious diseases.[7] The most important cause of IU is idiopathic (pars planitis) followed by sarcoidosis and tuberculosis.[7] The study has shown the following parameters of superficial capillary plexuses: 15–70 μm (below the internal plexiform layer) and deep capillary plexus 3 μm (below the internal plexiform layer) – 15 μm (below the internal plexiform layer).[1234568] In this study, inclusion and exclusion criteria in selecting the cases for the studies were made.[1] Macular microvascular changes in patients with IU using OCT-A were analyzed, and they tried to establish a relationship between the measurements of those plexuses with disease duration and disease activities.[1] Sixteen patients were investigated in the study (Eight males and eight females); the average age of the patients was 28.80 ± 12.80 years.[1] Macular thicknesses were measured using a Heidelberg Spectralis (Germany) machine where superficial and deep macular vessels were examined.[1] The parameters were compared with those of healthy volunteers.[1] Macular thickness was found to be higher in the patient group (P < 0.001).[1] Superficial and deep vessel densities were almost lower in all quadrants in the IU patient group (P < 0.05).[1] Macular thickness was increased in active disease but none of the OCT-A parameters showed a significant difference between the active and inactive diseases.[1] It was concluded that macular vessel density reduction was noted in both superficial and deep plexuses in IU.[1] These parameters could provide critical data to observe the IU cases in the follow-up.[1]

Some of the limitations of the study could be its fewer number of cases in the study.[1] Moreover, If the biomarkers of some etiological cases, for instance, serum angiotensin-converting enzyme levels in sarcoidal IU, could be correlated with those involved in microvascular changes, it would give more important clues in the disease-specific IU.[1] IU is also known for its complications in the macula.[17] Studying the temporal associations in IU or posterior uveitis with microvascular macular changes would be an interesting aspect to look at in future large-scale studies. Epi-retinal membrane formation is one of the important structural complications in IU. This was not seen in the present study which can affect the microvascular component in the macula.[1]

Fractal dimensional analysis of OCT-A refers to newer grayscale image modalities that demarcate superficial and deep plexuses in some of the retinal diseases, particularly diabetic retinopathy.[9] In diabetic eyes, the vascular density was also significantly reduced in superficial and deep plexuses, and applied fractal analysis to OCT-A imaging has potential pathological parameters in microvascular characteristics.[89] Fractals are the patterns found in nature and biological systems that show the same level of complexity and are compared from the usual general pattern drawn in a scale in which they are measured. The best part of the fractal geometric analysis is that a mathematical framework can be drawn on those biological structures.[9] Fractal analysis in OCT-A for retinal vasculature compared with future three-dimensional color fundus photographs and fluorescein angiography can tell us about the microvascular changes in a better way.[9] They can prognosticate severe retinal and uveitic diseases, calculate retinal threat stratification, and monitor disease management practices.[9]


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