Retinal Vascular Geometry in Hypertension: cSLO-Based Method

Abstract

Introduction: We aim to introduce a method using confocal scanning laser ophthalmoscopy (cSLO) images for measuring retinal vascular geometry, including vessel branch angle (BA), vessel diameter, vessel tortuosity, and fractal dimension (D_f), and to elucidate the relationship between hypertension and these metrics.

Methods: A total of 119 participants (119 eyes) were enrolled, among which 72 were normotensive and 47 were hypertensive. Infrared cSLO images were extracted from the circular scan around the optics disc using a commercial cSLO + optical coherence tomography instrument. Preprocessed cSLO images were further analyzed using the appropriate tool/macro/plugin of ImageJ.

Results: Intraclass correlation coefficients of selected methods used for conducting the cSLO-based geometric analyses were all higher than 0.80. Arterial/arteriolar BA, arteriolar vessel diameter, and total D_f in normotensive subjects were 85.80 ± 7.79°, 116.80 ± 12.58 μm, and 1.430 ± 0.037, respectively, significantly higher than those of hypertensive subjects (82.13 ± 10.83°, 108.2 ± 11.12 μm, and 1.361 ± 0.044, all P < 0.05). The aforementioned metrics remained negatively correlated with hypertension even after adjusting for age alone or age and gender (P < 0.05). However, the difference between arteriolar tortuosity and all studied venous/venular geometric parameters in both subjects was insignificant (all P > 0.05).

Conclusion: Proposed cSLO-based methods for assessing various vascular geometric parameters were highly repeatable and reproducible. Arterial/arteriolar BA, arteriolar vessel diameter, and total D_f were retinal vascular parameters significantly correlated with hypertension in a negative manner.

Keywords: OCT; Retinal vascular geometry; cSLO.

Fig. 1

cSLO image and measurement methods of various vascular geometric parameters. The cSLO image was acquired by the circular scan mode with four overlaid concentric circles. Compared with arteries (white asterisk), veins are thicker and darker and have a narrower light luminal reflex (blue asterisk). Zone A [0–0.5 disc diameter (DD) from the optic margin], zone B (0.5–1.0 DD from the optic margin), and zone C (0.5–2.0 DD from the optic margin) are labeled. b–d Magnified cSLO image (white box in a). The white arc represents the vessel branch angle. b Method 1 (vessel reflex to vessel reflex): all three measurement points (dots on the yellow line) are on the vessel reflex, two on the daughter’s vessels (blue arrow), and one on the parent vessel (green arrow). c Method 2 (plasma layers to plasma layers): all three points are on the plasma layers. d Method 3 (plasma layers to vessel reflex to plasma layers): two points are on the plasma layers, and one is on the luminal reflex. e–g Magnified cSLO image (blue box in a). The measurement of retinal vessel diameter and vessel tortuosity. e Positioning a through-line along the lumen. f The automatic generation of the cross-line perpendicular to the vessel with prespecified 10 μm space calculates vessel diameter on the basis of an intensity profile algorithm. g The blue line represents the actual length, and the white line the shortest length. h Fractal dimension within zone C after binarization and skeletonization

Fig. 2

Intra-rater repeatability of vessel branch angle (BA) measurement using Bland–Altman analyses. The Bland–Altman plot shows 95% limits of agreement (LoA) in arterial/arteriolar BA using methods 1 (a), 2 (b), and 3 (c) and venous/venular BA using methods 1 (d), 2 (e), and 3 (f) performed by the same operator

Fig. 3

Inter-rater reproducibility of vessel branch angle (BA) measurement using Bland–Altman analyses. The Bland–Altman plot shows 95% limits of agreement (LoA) in arterial/arteriolar BA using methods 1 (a), 2 (b), and 3 (c) and venous/venular BA using methods 1 (d), 2 (e), and 3 (f) performed by two operators

Fig. 4

Intra-rater repeatability and inter-rater reproducibility of vessel diameter, tortuosity, and total fractal dimension (D_f) measurement using Bland–Altman analyses. The Bland–Altman plot shows 95% limits of agreement (LoA) of intra-rater repeatability in arteriolar diameter (a), venular diameter (b), arteriolar tortuosity (c), venular tortuosity (d), and total D_f (e), and LoA of inter-rater in arteriolar diameter (f), venular diameter (g), arteriolar tortuosity (h), venular tortuosity (i), and total D_f (j)