Purpose To investigate the changes of the retinal microvascular network and microcirculation in high myopia. Design A cross-sectional, matched, comparative clinical study. Participants Twenty eyes of 20 subjects with nonpathological high myopia (28 ± 5 years of age) with a refractive error of −6.31 ± 1.23 D (mean ± SD) and 20 eyes of 20 age- and sex-matched control subjects (30 ± 6 years of age) with a refractive error of −1.40 ± 1.00 D were recruited. Methods Optical coherence tomography angiography (OCTA) was used to image the retinal microvascular network, which was later quantified by fractal analysis (box counting [Dbox], representing vessel density) in both superficial and deep vascular plexuses. The Retinal Function Imager was used to image the retinal microvessel blood flow velocity (BFV). The BFV and microvascular density in the myopia group were corrected for ocular magnification using Bennett's formula. Results The density of both superficial and deep microvascular plexuses was significantly decreased in the myopia group in comparison to the controls (P <.05). The decrease of the microvessel density of the annular zone (0.6–2.5 mm), measured as Dbox, was 2.1% and 2.9% in the superficial and deep vascular plexuses, respectively. Microvessel density reached a plateau from 0.5 mm to 1.25 mm from the fovea in both groups, but that in the myopic group was about 3% lower than the control group. No significant differences were detected between the groups in retinal microvascular BFV in either arterioles or venules (P >.05). Microvascular densities in both superficial (r = −0.45, P =.047) and deep (r = −0.54, P =.01) vascular plexuses were negatively correlated with the axial lengths in the myopic eye. No correlations were observed between BFV and vessel density (P >.05). Conclusions Retinal microvascular decrease was observed in the high myopia subjects, whereas the retinal microvessel BFV remained unchanged. The retinal microvascular network alteration may be attributed to ocular elongation that occurs with the progression of myopia. The novel quantitative analyses of the retinal microvasculature may help to characterize the underlying pathophysiology of myopia and enable early detection and prevention of myopic retinopathy.
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