Hemodynamic and morphological changes of the central retinal artery in myopic eyes

Abstract

Due to excessive elongation of the eyeball, myopia-related vascular abnormalities are frequently observed in the central retinal artery (CRA) and its intraretinal branches. In addition to inconsistency in previously reported findings, hemodynamic (reduced flow velocity, increased vascular resistance) and morphological changes (narrower vessel diameter) were usually studied separately. This cross-sectional study evaluated the hemodynamic and morphological characteristics concurrently in a large sample of healthy myopes, by using the color Doppler ultrasound and adaptive optics retinal camera. Results showed that the retrobulbar segment of CRA had a tendency of slightly reduced flow velocity in eyeballs with longer axial length, but the correlation was not significant after adjusting for the multiple correlations. Vascular resistance was not affected by the axial elongation. With respect to the intraretinal branches, no significant changes in longer eyes of total diameter or lumen diameter were observed, while both the wall thickness and the wall cross-sectional area were significantly increased, but only a marginally increase in the wall to lumen ratio was found with increasing axial length. This implies some potential small artery remodeling in the intraretinal CRA branches. Overall, blood supply of the inner retina in healthy young myopes is likely to be maintained. Additionally, morphological parameters of vascular microstructure could be potential biomarkers to monitor myopia progression and understand myopia-related vascular abnormalities in future studies.

Figure 1

Image processing to obtain the morphological parameters of the temporal branch of the central retinal artery. Raw images (a) from the adaptive optics fundus camera were automatically stitched, using i2k Retina Pro software (Version 3.1.0, DualAlign, LLC, Clifton Park, NY), to create the montage (b), which was later manually superimposed onto the infrared fundus image (c) to mark the measurement location (d), using Microsoft PowerPoint for Mac (Version 16.59, Microsoft Corporation, Washington, USA) and Fiji (Version 2.1.0/1.53c, Open source image processing package). The center and contour of the optic disc (point O) was automatically identified by the imaging software. The actual measurement location (point M) was about 0.75 disc diameter from the disc margin (distance between point G and H). Three adjacent measurements (e) were taken after correcting ocular magnification by the axial length. Total diameter, lumen diameter and wall thickness of the retinal artery were measured by the AOdetect Artery (version 2.0b17, Imagine Eyes, Orsay, France).

Figure 2

Measurement location and typical waveform of the central retinal artery (CRA) in color Doppler ultrasonography. The locations of the eyeball and optic nerve are outlined by the white circle and yellow ellipse, respectively. Blood flow signals (blue and red areas) appear within the green rectangle. Hemodynamic parameters, including peak systolic velocity (Vp), end diastolic velocity (EDV), time-averaged mean velocity (Vmn), pulsatility index (PI), resistive index (RI) and systolic / diastolic ratio (S/D), were calculated for each triple-waveform.

Figure 3

Bivariate Spearman correlations between axial length and hemodynamic parameters of the central retinal artery. Spearman correlation coefficients (rs), p-values and adjusted p-values after Bonferroni correction are presented.

Figure 4

Bivariate Spearman correlations between axial length and morphological analysis of retinal artery. Spearman correlation coefficients (rs), p-values and adjusted p-values after Bonferroni correction were presented.