The Effect of Axial Length on Macular Vascular Density in Eyes with High Myopia

Abstract

Objective: To evaluate the relationship between optical coherence tomography angiography (OCTA) findings and axial length (AL) in eyes with high myopia.

Materials and methods: A total of 122 eyes from 78 patients were included. Seventy-five eyes with an AL ranging between 26.00 and 27.49 mm comprised Group 1, and 47 with an AL of ≥ 27.50 mm comprised Group 2. Spectral-domain OCT was performed to measure the central macular thickness, subfoveal choroidal thickness (SCT) and swept-source OCTA was utilized to obtain the data on foveal avascular zone (FAZ) and vascular density (VD) values at the superficial and deep capillary plexuses (SCP and DCP), outer retina (OuR), and choriocapillaris (CC) segments.

Results: While no significant differences were found in terms of the mean superficial-FAZ and deep-FAZ areas (p=0.284 and p=0.952, respectively), there were significant differences between the groups in terms of the mean foveal VD in the SCP (p=0.001), the mean total VD (p=0.045) and foveal VD in the DCP (p<0.001), the mean foveal VD (p=0.019) and superior parafoveal VD in the OuR (p=0.008), the mean total (p=0.005), temporal parafoveal (p=0.034), inferior parafoveal (p=0.029), and nasal parafoveal VDs in the CC segments (p=0.005).

Discussion: The findings of the present study highlight the complex interplay between axial elongation and retinal microvasculature, suggesting that factors beyond mechanical stretching may contribute to these alterations. The variability in the existing literature on this topic arises from inconsistencies in the definition of high myopia, the use of different OCTA devices, and heterogeneous study populations. By including eyes with myopic maculopathy and employing axial length-based classification, this study provides a broad representation of high myopia. However, its retrospective design, single-center setting, and monoracial cohort represent limitations. Future large-scale, prospective studies involving diverse populations are needed to elucidate further the pathophysiology of high myopia and its impact on retinal and choroidal microcirculation.

Conclusions: Our study revealed that high-myopic eyes with longer ALs exhibited increased total VD in the DCP and increased foveal VD in the SCP, DCP, and OuR segments, while they showed decreased total VD and temporal, inferior, and nasal parafoveal VDs in the CC segment compared to high-myopic eyes with shorter ALs.

Keywords: AL = Axial length; BCVA = Best corrected visual acuity; BM = Bruch’s membrane; CC = Choriocapillaris; CFI = Color fundus image; CMT = Central macular thickness; DCP = Deep capillary plexus; EDI = Enhanced depth imaging; FAZ = Foveal avascular zone; HM = High myopia; ILM = Internal limiting membrane; META-PM = Meta-Analysis for Pathologic Myopia; MNV = Macular neovascularization; OCT = Optical coherence tomography; OCTA = Optical coherence tomography angiography; OuR = Outer retina; PS = Posterior staphyloma; RPE = Retinal pigment epithelium; SCP = Superficial capillary plexus; SCT = Subfoveal choroidal thickness; SE = Spherical equivalent; VD = Vascular density; degenerative myopia; foveal avascular zone; high myopia; optical coherence tomography angiography; vascular density.

Fig. 1

A. The measurements of the central macular thickness (CMT) (indicated in yellow) and subfoveal choroidal thickness (SCT) (shown in red) are illustrated on a transfoveal 7-mm horizontal spectral-domain optical coherence tomographic (OCT) section of the right eye of a 34-year-old male with an axial length (AL) of 27.40 mm; B. An active macular neovascularization is observed as a hyperreflective membrane above the retinal pigment epithelium, located within the outer retinal layers in association with intraretinal fluid on the transfoveal 7-mm horizontal spectral-domain OCT section of the right eye of a 63-year-old female with an AL of 28.54 mm; C. A posterior staphyloma is observed as an outward protrusion of sclera with a curvature radius smaller than the curvature radius of the adjacent sclera on the transfoveal 9-mm enhanced depth imaging OCT of a 33-year-old male with an AL of 29.31 mm

Fig. 2

Illustration of the 3 x 3 mm optical coherence tomography angiography findings of the right eye of a 26-year-old female with an axial length of 27.43 mm. The foveal avascular zone area was manually measured in the layers of the superficial capillary plexus (A) - yellow area and the deep capillary plexus (B) - red area. Vascular density (VD) values were recorded from the density map as the foveal (19.48%) and superior (49.89%), temporal (48.11%), inferior (47.83%), and nasal parafoveal (49.43%) VDs (C)