To analyze the repeatability of manual measurement of foveal avascular zone (FAZ) area in an optical coherence tomography angiography (OCTA) image in high myopia.
This study comprised patients with high myopia and controls. Two consecutive FAZ areas of the superficial and deep capillary plexus were obtained using OCTA. The intraclass correlation coefficient (ICC) and coefficient of variation (CV) were assessed, and univariate and multivariate generalized linear mixed models were conducted to identify factors related to repeatability.
Thirty eyes with high myopia and 34 eyes of healthy subjects were included in the study. The mean age in high myopia and control subjects was 55.5 and 60.8 years, respectively, the mean spherical equivalent was −9.98 and −0.55 diopters, and the mean axial length was 28.0 and 23.9 mm. The ICCs of FAZ area of the superficial capillary plexus (SCP) were 0.891 and 0.919, while the CVs were 8.8% and 8.5%. In measurement of the deep capillary plexus, the ICCs were 0.788 and 0.907, while the CVs were 11.2% and 11.0%, which were acceptable but exhibited lower repeatability than those of SCP. Multivariate analyses showed that older age (
Manual measurement of FAZ area using OCTA exhibited relatively good repeatability for high myopia. Age and axial length affected repeatability and should be considered when analyzing FAZ areas in high myopia patients.
High myopia is one of the most common causes of visual loss and is especially common in Asia. The prevalence of myopia is as high as 80% in Asia and 25% in other regions [
Recently, optical coherence tomography angiography (OCTA) has been developed to enable noninvasive, high-resolution retinal microvascular measurements. OCTA visualizes the microvascular flow in the retina by comparing the signals of successive B-scans at the same location to show the movement of erythrocytes. Due to its high axial resolution, OCTA can visualize multiple layers of micro-retinal vasculature that cannot be analyzed using fluorescein angiography [
The aim of this study was to analyze the repeatability of manual FAZ area measurements produced by OCTA when imaging high myopia patients without maculopathy.
This study adhered to the tenets of the Declaration of Helsinki and was approved by the institutional review board of Konyang University Hospital (2019-07-026) in the Republic of Korea. Informed consent was waived due to the retrospective nature of the study. This retrospective study involved patients admitted to our retina clinic from January 2018 to May 2019. The high myopia group consisted of eyes with an axial length ≥26.0 mm. The control group consisted of eyes with an axial length <26.0 mm and −6.0 diopters (D) < spherical equivalent (SE) <+3.0 D. We obtained a detailed history, best-corrected visual acuity (BCVA), intraocular pressure (IOP), SE, and axial length using the IOL Master (Carl Zeiss, Jena, Germany). The exclusion criteria were history of diabetes, hypertension, any kind of ophthalmic disease except high myopia, retinal disease, neuro-ophthalmic disease, BCVA <20 / 25, or IOP >21 mmHg. We also excluded patients with posterior staphyloma, diffuse chorioretinal atrophy, vitreous macular traction, and myopic choroidal neovascularization to obtain an accurate image and analysis.
OCTA was performed using the Spectralis OCT2 device (Heidelberg Engineering, Heidelberg, Germany). For each subject, measurements were performed twice with a 5-minute interval at the initial visit. The Spectralis OCT2 instrument is capable of 70,000 A-scans/s using a light source centered at 870 nm, with axial and transverse resolutions of 3.9 and 6 µm in tissue, respectively. In this study, a 20 × 15-degree-pattern OCTA scan centered on the fovea was acquired. En face images of the superficial capillary plexus (SCP) and the deep capillary plexus (DCP) were visualized automatically by segmenting two separate slabs defined by the arbitrary segmentation lines created by the software of the device. The SCP is defined as the layer originating from the internal limiting membrane to the inner plexiform layer. The DCP is defined as the layer that starts from the outer border of the inner plexiform layer and travels to the outer border of the outer plexiform layer. Two graders (JHL and MWL) manually outlined the FAZ, defined as the avascular area in the center of the fovea, and measured the area using the inbuilt program that provides measurement of the outlined area. A mean value of two measurements was used for analysis (
To analyze the repeatability of FAZ area measurements of the SCP and DCP in high myopia patients, the intraclass correlation coefficient (ICC) and coefficient of variation (CV) were calculated. ICC is the correlation between two variables measured at the same time point, with values ranging from 0 to 1 (<0.40, poor; 0.40–0.59, fair; 0.60–0.74, good; 0.75–1.00, excellent). The CV (%) was calculated as 100 × standard deviation/overall mean, and a value <10% represents good repeatability of the measurement. The agreement between the two measurements was evaluated using Bland-Altman plots.
To identify factors affecting the repeatability of FAZ area measurements, univariate and multivariate generalized linear mixed models were used. Statistical analyses were performed using PASW Statistics ver. 18.0 (SPSS Inc., Chicago, IL, USA).
A total of 64 eyes was included: 30 eyes in the high myopia group and 34 eyes in the control group. The mean age, BCVA, and IOP were 55.5 ± 13.5 and 60.8 ± 9.8 years, 0.09 ± 0.09 and 0.07 ± 0.07, and 14.0 ± 2.1 and 13.3 ± 3.6 mmHg, respectively, and they were not significantly different (
The FAZ areas measured by the two graders exhibited excellent interobserver reproducibility (ICC >0.95, CV <5%). The first measurements of the mean FAZ areas of the SCP in the high myopia and control groups were 0.35 ± 0.13 and 0.25 ± 0.10 mm2, respectively (
In the Bland-Altman plots, measurements in the DCP exhibited lager scatter compared to those in the SCP (
Univariate analysis showed that age (coefficient, 0.01;
In terms of repeatability of DCP FAZ area measurements, sex (coefficient, 0.08;
The term repeatability implies the degree of consistency between independent measurements obtained with the same instrument on identical test materials under the same conditions (i.e., the same operator performing consecutive measurements). Repeatability is an indicator of the applicability of any instrument as a diagnostic tool in clinical practice. Repeatability is particularly important to determine the significance of differences that may be observed over time or between normal and diseased eyes. Previous studies have reported high repeatability of OCTA measurements in normal eyes [
Recently, several studies have reported the FAZ area in high myopia patients. Sung et al. [
The CVs of the high myopia and control groups were not very different in both the SCP and DCP. However, considering that the CV was calculated as 100 × standard deviation/overall mean, and the areas of the superficial and deep FAZs were larger in the high myopia group, it was determined that the high myopia group had relatively lower repeatability than the healthy subjects even though the CV was similar in both groups. Additionally, we found high repeatability, with an ICC of 0.891 and a CV of 8.8% for the FAZ areas in the SCP, and reasonable repeatability, although relatively lower than that of SCP, with an ICC of 0.788 and a CV of 11.2% of the FAZ areas in the DCP in the high myopia group. This may be explained by the fact that the analysis of SCP was more accurate than that of DCP because of projection artifacts. Projection artifacts occur in modern practice when the light passing through the vessel fluctuates over time, illuminating anything posterior to the vessel. Artifactual images of the vessels may then be seen at deeper locations in the eye than where they actually exist [
Our study showed that age was one of the significant factors affecting the variation in manual FAZ area measurements in the SCP using OCTA images (coefficient, 0.01;
Axial length was the significant factor affecting the variation in manual FAZ area measurements in both the SCP and DCP. Rao et al. [
Our study had several limitations. In addition to the small sample size, other microvascular parameters such as vessel density or perfusion density were not analyzed. Additionally, Lee et al. [
In conclusion, manual measurements of FAZ area using OCTA images showed relatively good repeatability in patients with high myopia. Additionally, age and axial length affected such repeatability and should be considered when analyzing FAZ area in high myopia patients.
Values are presented as mean ± standard deviation or number (%).
BCVA = best-corrected visual acuity; logMAR = logarithm of the minimal angle of resolution; IOP = intraocular pressure.
FAZ = foveal avascular zone; ICC = intraclass correlation coefficient; CV = coefficient of variation.
*Statistically significant.
CI = confidence interval; BCVA = best-corrected visual acuity; IOP = intraocular pressure; PPA = peripapillary chorioretinal atrophy.
*Statistically significant.
CI = confidence interval; BCVA = best-corrected visual acuity; IOP = intraocular pressure; PPA = peripapillary chorioretinal atrophy.
*Statistically significant.