Characterization of Vortex Vein Drainage System in Healthy Individuals Imaged by Ultra-Widefield Optical Coherence Tomography Angiography

Abstract

Purpose: The purpose of this study was to investigate the choroidal characteristics of vortex vein (VV) drainage systems in healthy individuals using ultra-widefield optical coherence tomography angiography.

Methods: The mean choroidal thickness (ChT) and choroidal vascularity index (CVI) of each VV quadrant (24 × 20 mm2 scan mode; superotemporal [ST], superonasal [SN], inferonasal [IN], and inferotemporal [IT] quadrants) were calculated. Furthermore, intervortex venous anastomosis (IVA) was classified into temporal, superior, inferior, and nasal types.

Results: A total of 207 healthy eyes were analyzed to find that the ST quadrant had the thickest choroidal layer and highest CVI (all P < 0.05). Among the four VV drainage quadrants, the mean ChT and CVI decreased in the sequence of ST, SN, IT, and IN (all P < 0.05). Moreover, men had a higher CVI than women in all VV quadrants (all P < 0.05). IVA was observed in all VV quadrants of 91 eyes (43.96%), and in the macular region of 33 eyes (15.94%).

Conclusions: The ST drainage system was identified as the preferred VV drainage route in healthy eyes. Among the four VV drainage quadrants, the drainage system adhered to the ST-SN-IT-IN order of descending perfusion. Furthermore, age- and sex-related differences were noted in the choroidal VV drainage systems of healthy eyes. Additionally, almost half of the healthy eyes had IVA in their choroidal vessel networks.

Translational relevance: The VV drainage system may be considered a novel imaging biomarker for ocular diseases.

Figure 1.

(A) OCTA imaging protocol. Five 24 × 20 mm² choroid medium-to-large vessel images in predefined locations (central, ST, SN, IT, and IN quadrants) on the right eye of a healthy 50-year-old man were obtained. ChT and CVI were collected for a 9 × 9 mm² area (red dotted boxes; ST, SN, IT, and IN quadrants) and a 6 × 6 mm² area (red dotted box; central quadrant). The mean ChT (B) and CVI (C) decreased in the order of ST–SN–IT–IN. The ChT map (B) and choroid medium-to-large vessel image (C) were obtained from the right eye of a healthy 38-year-old man. (D) Bar graphs showing the quantification of the ChT of healthy eyes in the ST, SN, IN, and IT drainage quadrants. (E) Bar graphs showing the quantification of the CVI of healthy eyes in the ST, SN, IN, and IT drainage quadrants. Data are reported as mean ± SEM, based on repeated measures ANOVA. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001. (F) Line graphs of ChT in the submacular area and the ST, SN, IN, and IT drainage quadrants for the 20 to 80 age group. (G) Line graphs of CVI in the submacular area and the ST, SN, IN, and IT drainage quadrants for the 20 to 80 age group. (H) Bar graphs of the population divided into age groups. OCTA, optical coherence tomography angiography; ST, superotemporal; SN, superonasal; IT, inferotemporal; IN, inferonasal; ChT, choroidal thickness; CVI, choroidal vascularity index; ANOVA, analysis of variance.

Figure 2.

(A, C, E, G) Associations between ChT and age in the ST, SN, IT, and IN drainage quadrants, respectively. (B, D, F, H) Associations between CVI and age in the ST, SN, IT, and IN drainage quadrants. respectively. (I, K, M, O) Associations between ChT and AL in the ST, SN, IT, and IN drainage quadrants, respectively. (J, L, N, P) Associations between CVI and AL in the ST, SN, IT, and IN drainage quadrants, respectively. ChT, choroidal thickness; CVI, choroidal vascularity index; ST, superotemporal; SN, superonasal; IT, inferotemporal; IN, inferonasal; AL, axial length.

Figure 3.

UWF en face choroidal maps (> 200 degrees). IVAs in the temporal (A), superior (C), inferior (E), and nasal (G) quadrants are highlighted in yellow (B, D, F, and H). Red asterisks indicate the vortex vein (VV) ampullas in adjacent quadrants, whereas the red arrows refer to the anastomotic vessels connecting the VV ampullas in adjacent quadrants. UWF, ultra-widefield; IVAs, intervortex venous anastomoses.