Myopic Vascular Changes Revealed by Optical Tomography Angiography and Their Association with Myopic Fundus Manifestations

Myopia is one of the most prevalent eye conditions, affecting 81.6–96.5% of the world’s population [1‒3]. Severe myopia is associated with an increased risk of other ophthalmic conditions, including multiple maculopathies such as posterior staphyloma and chorioretinal atrophy [4]. Previous studies have discovered that pathological myopia is characterized by specific fundus manifestations. Typical features include tessellation, parapapillary atrophy (PPA), lacquer cracks, and choroidal neovascular membranes [5]. Myopic fundus degeneration often comes with vascular alterations and complications, including the emergence of neovascularization or loss of choriocapillaris. There may be reciprocal causation between such microvasculature changes and myopic retinopathy. Their rich dynamics are vital in pathological myopia pathogenesis [6].

Optical tomography angiography (OCTA) is a noninvasive technique for microvasculature imaging of the retina and choroid without using intravascular dyes. It segments the eyes into different areas and illustrates vessels through the light reflectance of the moving red blood cell surface [7]. Many studies have used OCTA to reveal myopic microvascular changes, such as retinal vascular density (VD) [8], choroidal thickness, and choriocapillaris blood perfusion [9]. However, to our knowledge, no study has combined vasculature visualization and ultra-widefield (UWF) fundus imaging. We aimed to explore the potential associations between vascular features and fundus manifestations of myopia using two different modalities of measurements: swept-source optical tomography (SS-OCT)/OCTA and UWF fundus camera, hoping to help elucidate the role of microvasculature during myopic retinopathy pathogenesis.

In this cross-sectional study, we enrolled 75 patients with myopia recruited at the Eye and ENT Hospital of Fudan University from September to November 2021. The inclusion criteria were as follows: (1) age between 18 and 65 years, (2) spherical equivalent (SE) ≤ −0.75D, and (3) intraocular pressure (IOP) <21 mm Hg. Exclusion criteria were a history of ocular surgery or trauma and concomitant ophthalmic diseases other than myopia, such as uveitis, cataract, glaucoma, and other systemic diseases with potential impact on ocular health. Only the right eye of each patient was included in this analysis. This study was approved by the Ethics Committee of the hospital (ID: 2016038), and written consent was obtained from all patients.

All patients underwent a broad set of ocular examinations, including manifest refraction (RT-5100; Nidek Technologies, Japan), IOP (Tonemeterx-10; Canon, Tokyo, Japan), axial length (AL) (IOL Master 700, 128 Carl Zeiss Meditec, Dublin, CA, USA), keratometry, anterior segment scanning (Oculus Pentacam HR, Oculus Optikgerate Wetzlar, Germany), and slit-lamp examination. Patients were divided into two groups based on the SE: low and moderate myopia (LMM, −6.00D ≤ SE < −0.75D) and high myopia (HM, SE ≤ −6.0D).

All patients were required to apply topical 0.5% tropicamide to their eyes every 5 min, and the process was repeated five times. Previous studies have revealed that mydriasis has little impact on the vasculature parameters of the choroid and retina [10], suggesting that cycloplegic agents did not confound the study’s results. Approximately 30 min after the last drop of tropicamide, SS-OCT/OCTA examinations were performed by an ophthalmologist using the same equipment (VG200D; 146 SVision Imaging Ltd., Luoyang, China). A modified version of early treatment diabetic retinopathy study (ETDRS) grids was adopted to determine four measurement zones: four concentric circles of diameters 1, 3, 6, and 9 mm (Fig. 1) centered on the fovea, namely, a 9-mm circle was added on the basis of the original ETDRS grids. For a clear illustration, the numerical value of the diameter was added to each OCTA parameter as a number suffix to distinguish between different measurement zones (for example, FA-OR1 means the flow area of the outer retina in the 1-mm diameter circle). The built-in algorithm automatically segmented the layered structures of the fundus and calculated different dimensions of the OCTA parameters within the given zones, including flow area, thickness, and VD. The magnification was corrected using the Benett formula as described before [11]. The complete list of measured OCTA parameters and their abbreviations is presented in online supplementary Table 1 (for all online suppl. material, see https://doi.org/10.1159/000531877).

All patients underwent UWF fundus imaging by an experienced ophthalmologist using Clarus 500™ (Carl Zeiss Meditec, Inc., Dublin, CA, USA) in a dark room after proper mydriasis as described above. For each patient, the picture with the best image quality was selected for analysis. Two ophthalmologists reviewed and rated the UWF fundus images in a blinded manner. A third senior specialist re-evaluated the images when different opinions were received. The UWF fundus image evaluation was performed using Adobe Photoshop CC 2017 (Adobe Systems Incorporated, San Jose, CA, USA). The diameters of the optic cup, optic disk, central artery, vein of the retina, and area of the PPA were measured as the number of pixels (online suppl. Fig. 1). Tessellation was graded into five categories, T0–T4, based on a previously reported grading system (T0: no tessellation; T1: tessellation involvement of the outer 6–9 mm annulus; T2: involvement of the 3–6 mm annulus; T3: involvement of the 1–3 mm annulus; T4: involvement of the central 1-mm circle) [12]. As the tessellation location becomes more central and adjacent to the fovea, the higher the grade becomes. Optic disk tilt was defined as an ovality index (the ratio of the shortest diameter of the optic disk to its longest diameter) smaller than 0.7 [13, 14]. Tessellation and vessel diameter were evaluated using the red and green channel images generated by the monochrome light emitting diodes of Clarus 500, respectively (online suppl. Fig. 2). Other fundus parameters were measured using regular color images. Detailed evaluation methods are described in online supplementary material.

All statistical analyses were performed using SPSS (version 25.0, IBM Corp., Armonk, NY, USA). The Kolmogorov-Smirnov test was used to examine whether the data were normally distributed. For normally and non-normally distributed samples, an independent samples t test or Mann-Whitney U test was performed for intergroup comparison. Pearson’s χ² test was used to compare categorical data. The relationship between the different OCTA parameters, AL, and fundus manifestations was assessed using Spearman’s correlation analysis. Results of UWF examination based on color images and monochrome channel images were compared using paired t test. All numerical values were transformed into Z-scores in a heatmap for direct visualization and comparison. Statistical significance was set at p < 0.05 for all tests.

The demographic and basic ophthalmic characteristics of the participants are summarized in Table 1. There was no significant difference in age, sex, IOP, or anterior chamber depth between the two groups. The AL and corneal thickness in the HM group were significantly higher than that in the LMM group.

All three categories of OCTA parameters for patients with HM and LMM are illustrated in Figure 2 as a heatmap. Statistically significant results are listed in Table 2. Owing to the large number of parameters included in the analyses, only statistically significant results are listed in the table. The flow area of the outer retina (FA-OR) was significantly higher in HM in all zones except for the 1-mm diameter circle, whereas the thickness of choroid (TC) was smaller in all four measured zones. Flow areas of the inner retina (FA-IR), angio choroid (FA-AC), and choriocapillaris (FA-CC) were similar between the LMM and HM groups. There were no significant differences in the thickness of retina (TR), the thickness of ganglion cell layer and inner plexiform layer, or vessel density in both the deep (VD-D) and superficial vascular complexes (VD-S).

To further investigate the intrinsic mechanisms of myopia-induced, axial elongation-mediated ocular changes, we analyzed the correlation between OCTA parameters and AL (Table 3). Spearman correlation analyses revealed that the blood flow in the choroid was impaired in patients with longer AL as there were significant negative correlations between FA-AC, FA-CC, and AL in the 3, 6, and 9-mm circle areas, respectively. TC remained a robust biomarker, exhibiting the strongest stable negative correlation among the OCTA parameters in all four measured zones. TR was also negatively associated with AL, but only in the 9-mm diameter zone.

Table 4 summarizes the findings regarding fundus manifestations in the UWF fundus images in the LMM and HM groups. There was a clear tendency for larger optic disk diameter (254.13 ± 28.74 vs. 278.30 ± 55.88, p = 0.018) and PPA area (10,017 ± 8,591 vs. 22,206 ± 15,017, p < 0.001) in patients with HM, and smaller vessel size in the central artery (11.20 ± 1.98 vs. 9.87 ± 1.92, p < 0.001) and vein (16.06 ± 2.43 vs. 14.36 ± 1.78, p < 0.001) of the retina (Fig. 3a). The proportion of patients with disk tilt was also higher in the HM group (39% vs. 27%), although the difference was not statistically significant from the χ² test (p = 0.285) (Fig. 3b). There were no significant differences between the LMM and HM groups in the cup-to-disk ratio, optic cup diameter, or artery-to-vein diameter ratio (Table 4). The distribution of tessellation grades was significantly different between both groups. All patients with T4 tessellation belonged to the HM group, whereas patients with LMM majorly had T0 and T1 tessellation (Fig. 3c). By comparing the results of monochromatic channel images and the original color images, no difference was found based on current tessellation grading system, but the vessel diameter measured in green channel images were narrower, although absolute disparities were small (online suppl. Table 2). Besides tessellation and PPA, patchy atrophy (PA) was found in 6 patients (all in HM group), and no patient presented with macular atrophy.

We investigated the underlying correlation between fundus vascular structures and characteristic fundus manifestations in myopic eyes using Spearman correlation analyses (Table 5). FA-OR and TC were both correlated with PPA and tessellation in all measured zones, except for FA-OR and tessellation in the - mm circle. TR had a negative correlation with tessellation in the 9-mm circle and a negative correlation with PPA in the 3- and 9-mm circles. In the inner vascular retina, the vessel densities and flow area were reduced in eyes with higher grades of tessellation as vessel density of inner retina (VD-IR), VD-S, VD-D, flow area of angio retina, and FA-IR all revealed a negative correlation with tessellation in two or more zones.

OCTA and UWF fundus imaging are two approaches that describe fundus changes from different perspectives: microcosmic vascular structure, and macroscopic macular manifestations. Myopia can lead to AL elongation, followed by inevitable stretching and thinning of the choroid and other structure [4, 15]. Consequently, these physical alterations and mechanical forces can change the chorioretinal physiological environment, negatively impact the microvascular network, and participate in the formation of pathological fundal lesions. Traditional fundus cameras are limited by their shooting scope and low resolution. UWF fundus photography has facilitated the examination of more peripheral retinas. By providing a substantially wider field of view, the UWF fundus camera can cover a larger area of the fundus and capture more lesions during examination, thereby increasing diagnostic sensitivity. Moreover, the newest UWF fundus camera adopted in this study, Clarus 500, features true coloration closely resembling the fundus seen during fundoscopy, which aids in diagnosing ocular lesions and diseases where color is essential. Clarus 500 also consists of red, green, and blue light emitting diodes, which sequentially illuminate to generate true color images. Examiners can view a monochrome image of each composite color in order to better observe different structures and lesions in the fundus. To better decipher the complicated interactions underlying these interwinding processes, we combined OCTA and UWF imaging results to present a comprehensive landscape of the myopic fundus while simultaneously seeking their intrinsic association.

According to the SS-OCT/OCTA equipment used in this study, the detailed segmentation of each layer and nomenclature of the OCTA parameters are specified in online supplementary Table 3. FA-OR refers to the flow area of the avascular outer retina, starting at the middle of the outer plexiform layer, covering the entire layer of the retinal pigment epithelium (RPE) and ending 10 μm above Bruch’s membrane [6]. Therefore, the increase in FA-OR observed in HM may indicate abnormal neovascularization and could be interpreted as a form of retinal neovascularization [16]. Previous studies have confirmed that neovascularization is a common complication in pathologic myopia [17, 18]. Myopia induced ocular globe elongation, and the tractional force is transmitted from the inner to the outer retina, leading to the widening of the outer lamellar or even gradual detachment of the RPE. Moreover, disruption of the retinal structure increases the likelihood of retinal disorganization and other conditions, such as foveoschisis, retinoschisis, retinal/foveal detachment, and macular holes [19]. These conditions may affect retinal structural integrity, resulting in a wider scope being identified as the outer retina and, consequently, a higher FA-OR value.

Myopia can take a toll on the choroid. As the most vascularized ocular tissue, the choroid plays a vital role in myopia progression. Thinning of the choroid is a striking feature in myopia, and a negative correlation has been reported between choroidal thickness and AL [20, 21], similar to our finding of a smaller TC in the HM group. TC appeared to be the most important index among all OCTA parameters, exhibiting apparent differences between the HM and LMM groups and revealing a stable correlation with AL in all measured zones (Table 3). In addition to the choroidal thinning associated with AL [22], the rate of TC change is inversely related to the speed of axial elongation [23]. These findings suggest that TC has abundant clinical significances to explore and could serve as an ideal predictor of ocular elongation and myopia progression [24].

SE as a classification criterion did not yield significant results on choroidal vasculature; thus, we selected AL as the primary independent variable for further analyses (Table 3). AL had significant negative correlations with FA-CC and FA-AC, which were not significant when SE was chosen as the classification variable. The negative correlation coefficients suggested that with AL elongation, choroidal perfusion decreases with choroid thinning. The choriocapillaris is the innermost layer of the choroid and is responsible for RPE and photoreceptors’ nourishment [25]. Reduced choriocapillaris perfusion is of greater clinical significance for retinal function. In chickens with form-deprivation myopia, electron microscopy has revealed wall thickening, lumen narrowing, gap occlusion, and reduced capillary permeability, all of which could be the mechanism of flow area reduction in the choroid and choriocapillaris [26]. TCs correlation with AL remained stable across all measured zones, whereas TR was correlated with AL in the 9-mm circle alone. In comparison, TC decreased more drastically than TR in patients with myopia. Choroidal thickness was the main indicator of myopic fundal changes, closely connected with SE and AL. Moreover, as a direct ocular structural feature, AL has proven to be more valuable than SE in monitoring the progression of myopia and its related microvasculature changes in the choroid and choriocapillaris.

We did not observe any significant differences in retinal VD between LMM and HM or any significant correlation between VD and AL, which contradicts the findings of some studies. Ucak et al. [27] discovered that the VD-D and VD-S were lower in patients with HM than in healthy controls. Yaprak reported that the VDs of the superficial capillary plexus and deep capillary plexus were lower in the HM group than in the control group [28]. The different results in our study may be due to our relatively small sample size. Additionally, in prior studies, VD was compared between emmetropia and HM. In our study, all participants had different levels of myopia, and intergroup differences in VD were not statistically significant. This suggests that VD could be a distinguishing factor, separating myopic and non-myopic eyes; however, VD reduction may be proportional to an increase in refractive error or ocular globe elongation since VD did not differ between LMM and HM in this study. Changes in VD could be more sensitive in certain quadrants or regions. Shi et al. [29] discovered that VD-S was reduced only in the para-inferior region. However, when evaluated as a whole, the differences may be diluted and become insignificant.

Fundus manifestations of HM have been widely studied. In the study, using UWF fundus imaging, ophthalmologists can extensively examine retinal and macular changes in a wider scope with high-resolution and true-color images. In our study, most of the findings revealed by UWF were consistent with existing knowledge of myopic fundal changes, such as narrowing vessel diameter [30] and a higher proportion of disk tilt [14]. Clarus 500 provided monochrome image of three composite colors, facilitating observation of more delicate structures. Red channel image increased the visibility of tessellation, even though the grading results were the same in the study. Green channel image enhanced the outline of retinal blood vessels. The vessel wall was relatively more blurred and difficult to distinguish against the red-orange background in regular color images, hence resulted in slightly larger values of vessel diameter measurement compared with measurement in green channel images (online suppl. Table 3). Since we aimed to explore the association between fundus manifestations in UWF images and the structural and vascular features that were revealed by OCTA, we narrowed down further analyses around PPA and tessellation, two common phenomena observed during myopia progression. Previous studies have revealed that PPA enlargement was associated with axial elongation and consequent vascular trunk dragging [31]. Choroidal thinning in the parapapillary region also plays a major role in PPA [32]. The negative correlation between TC and PPA observed in our study validates this point. Since PPA was related to thinning and irregularities in the layers of the retina and RPE [33], the negative correlation between PPA and TR in this study was consistent with the definition of PPA. The PPA also exhibited a negative correlation with TR in the 3-mm circle, which typically included the parapapillary region where the PPA was located. One study reported that PPA is associated with the local microvasculature of the superficial and deep parapapillary vessels [34]. In this study, we did not quantify VD in the parapapillary region; however, there were no significant correlations between PPA and retinal VD in more general scopes based on the current data.

Fundus tessellation is defined as visible choroidal vessels at the posterior fundus pole due to the decrease of pigmentation in the RPE [35], often occurring in certain types of primary open-angle glaucoma [36] and myopic retinopathy [37]. Previous studies have linked fundus tessellation with choroidal thickness [38] in accordance with our observations. However, TR had a weaker correlation with tessellation in the 9-mm circle alone, which supports evidence from a previous study that a decrease in choroidal thickness instead of retinal thickness significantly contributed to the formation of tessellation [39]. We discovered that VD and FA also decreased in the inner retina as tessellation progressed: VD-IR, VD-S, and VD-D were negatively correlated with tessellation grade. This aligns with Sun’s findings, which revealed that higher VDs of retinal superficial capillary plexus and deep capillary plexus were protective factors for chorioretinal atrophy [40]. Similarly, Wang et al. [41] discovered that eyes with a tessellated fundus had a lower retinal flow index and VD than the control eyes. The FA-IR and flow area of angio retina findings were consistent with VD, all suggesting suboptimal blood perfusion of the inner retina. As tessellation became more severe, the inner retina and the overall retina’s flow area underwent shrinkage with decreased VDs.

We noticed that for most OCTA parameters, their absolute values of Spearman ρ with tessellation were larger in the 9-mm circle and smaller in the 1-mm parafovea region. This suggests that vascular and structural changes and their related myopic maculopathy were more sensitively and thoroughly reflected in the 9- and 6-mm diameter circles; thus, the correlation was stronger in a broader scope than in a narrower central scope. When the inspection area was larger, more information was available for analysis, fewer details were omitted, and the sensitivity and accuracy of diagnosis were higher, partly explaining the stronger correlation observed in a broader scope. In addition, compared with the fovea, the more peripheral parafoveal and perifoveal regions were more susceptible to myopia-induced alterations. Park et al. discovered that macular thickness alterations in myopic eyes were most apparent in the peripheral region and least in the central region [42]. Lindner studied the directional kinetics of atrophy progression and discovered that atrophy lesion progression toward the periphery was 2.8-fold faster than that toward the fovea [43]. This verified that the central retina was less susceptible to myopia-induced alterations; therefore, the correlation between the vasculature and fundal changes was weaker in this zone. The fovea plays the most crucial role in central vision, at which visual acuity is at its highest; thus, certain protective mechanisms could compensate for the effect of mechanical stretching on the fovea. A similar phenomenon has been reported for foveal-sparing geographic atrophy [44]. Jonas et al. [45] reported that retinal thinning was most apparent in the equatorial and pre-equatorial regions in myopic axial elongation, whereas foveal retinal thickness was mostly unaffected. The same tendency was observed in the choroid. In non-pathologic myopia, the choriocapillaris flow deficit percentage was discovered to be increased in the perifovea but not in the fovea or parafovea fields [46]. These studies provide a potential explanation for why the OCTA parameters of the 6- and 9-mm circles had a stronger association with tessellation. Therefore, adopting a broader field during ophthalmic examination might help detect more subtle changes at an earlier phase that may otherwise be overlooked, necessitating the application of widefield and UWF equipment in clinical practice.

Six patients were found with PA in the study. Because the number of patients with PA was small, and the extent of their PA was limited upon initial evaluation, we assumed that the effect of PA on the study would be limited, thus these patients were not ruled out from the study. Nevertheless, the existence of PA could have some adverse influence on the fundus [47] and fundal vasculature [48], which could amplify the correlation between fundus manifestation and OCTA parameters that were negatively affected by PA. This was a limitation of the study that should be noted.

The following recurring patterns and trends were summarized based on our findings. First, FA-OR could be considered as a negative biomarker in myopia because higher FA-OR was related to more severe myopia, larger PPA, and higher grade of tessellation. Second, the TC is a highly valuable OCTA parameter. It strongly correlates with other fundus manifestations and exhibits sensitive changes with axial elongation and myopia progression. In contrast, TR had weak correlations with AL, PPA, and tessellation only in the 9-mm circle, indicating that the retina was much more stable than the choroid in terms of thickness.

This study had some limitations. First, angiography quantification was not further divided into more specific quadrants, such as temporal and nasal. Thus, certain areas of particular interest, including the parapapillary region, were not analyzed separately. This restricted further exploration of PPA pathogenesis since PPA was a focal lesion. Second, we did not enroll healthy non-myopic participants as controls; therefore, comparisons were not conducted between emmetropia and myopia. Third, PA was not excluded from the study, which could affect certain OCTA parameters as was discussed above. Finally, due to the study’s cross-sectional nature, we could not conclude the causality between the observed phenomena and findings, except for some potential explanations and hypotheses. Further studies are required to elucidate these underlying mechanisms.

We conducted a combined analysis using data from OCTA and UWF fundus cameras and reported the existence of higher FA-OR and smaller TC in patients with HM, the negative correlation between choroidal vasculature and AL, and the connection between OCTA parameters and common myopic fundus manifestations. FA-OR and TC affected PPA and tessellation, while flow area and VD-IR were also associated with tessellation formation. Our findings may aid in understanding myopic retinopathy and its related vascular and structural fundal changes.

We would like to thank Editage (www.editage.cn) for English language editing.

This study followed the tenets of the Declaration of Helsinki and was approved by the Ethics Committee of Fudan University Eye and ENT Hospital Review Board (Shanghai, China, ID: 2016038). Written informed consent was obtained from all participants.

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Written informed consent was obtained from the patients for the publication of this paper. Patient names and the eyes/facial region of study participants are not applicable.

Funding was provided by Shanghai Rising-Star Program (21QA1401500) (Meiyan Li), Project of Shanghai Science and Technology (Grant No. 20410710100) (Xingtao Zhou), and Project of Shanghai Xuhui District Science and Technology (2020-015) (Xingtao Zhou).

Study concept and design: Y.X., W.Y., X.W., X.Z., M.L.; data collection: Y.X., Y.W., L.N., M.L.; data analysis and interpretation: Y.X., Y.W., M.L.; drafting of the manuscript: Y.X., Y.W.; critical revision of the manuscript: W.X., X.Z., M.L.; supervision: X.W., X.Z., M.L. All authors read and approved the final manuscript.

The datasets generated and/or analyzed during the current study are not publicly available due to funding requirement but are available from the corresponding author on reasonable request.

Yijia Xu and Weiming Yang contributed equally to this work and were considered co-first authors.