Capillary perfusion of superficial retina and hemodynamics of central retinal artery in myopic eyes

Purpose : Recent studies have shown that myopic eyes had reduced capillary perfusion of the superficial retina measured by Optical Coherence Tomography Angiography (OCTA). Blood supply of the superficial retina is originated from the central retinal artery (CRA), in which reduced blood flow velocities and increased blood vessel resistance in myopic eyes were also observed by Color Doppler Ultrasound (CDU). This cross-sectional study aimed to examine the association between impaired capillary perfusion and compromised CRA hemodynamics in myopes. Methods : 108 young healthy subjects (68 female and 40 male) aged from 18 to 40 and refractive errors of -0.25 to -15.38D were recruited. Subjects with systemic or ocular diseases which might affect ocular blood circulation were excluded. Axial length (AL) was measured by the IOL master. A 3 x 3 mm OCTA image centered on the fovea was captured using the Cirrus HD-OCT and perfusion densities of the superficial retina were calculated based on a 3mm-Early Treatment Diabetic Retinopathy Study grid. Hemodynamic characteristics (peak velocity, mean velocity, pulsatility index, PI, resistance index, RI) of the CRA were measured by MyLab™ Twice CDU with a linear transducer. Blood pressure and pulse were recorded by an electronic sphygmomanometer. Results : With an increase in AL, global perfusion density of the superficial retina (r = -0.33, p < 0.001), peak velocity (r = -0.22, p = 0.02) and mean velocity (r = -0.21, p = 0.03) of the CRA significantly decreased while the pulsatility and resistance indices remained unchanged. No significant correlation between the global perfusion density and hemodynamics characteristics of CRA was found after controlling for AL (all p > 0.05). However, results from generalized linear model showed that PI (B = 2.24, p = 0.03) and RI (B = 8.81, p = 0.01) were significant positive predictors of the perfusion density at the superior retinal region. Conclusions : In line with previous studies, both global perfusion density of superficial retina and blood flow of CRA were reduced in myopes. However, no causal relationship was found between reduced superficial capillary perfusion and compromised blood supply of CRA. Decreased CRA blood velocity does not necessarily lead to reduced blood volume entering the eye. The vessel lumen should be taken into consideration when examining the relationship between perfusion density and CRA hemodynamics.