To investigate the changes in the choroidal thickness (CT) and blood flow in pathologically myopic eyes using swept-source optical coherence tomography.

Using a cross-sectional design, a total of 40 subjects who visited the Eye Hospital, Wenzhou Medical University from September 2019 to June 2020 were included and divided into two groups: 20 cases of high myopia and 20 cases of pathological myopia, which were imaged with VG200 OCT in the 12 mm scan area of the subjects' right eyes centered on the central macular fovea. Then custom-built software was used to measure the CT of the macular central concavity within a diameter of 6 mm, and the images were binarized to calculate the choroidal vascular index (CVI).

Compared to highly myopic eyes, pathologically myopic eyes had decreased CT and CVI in the 6 mm range centered on the macula. CT in the 6 mm range was 171±54 and 92±37 μm in the vertical direction (t=5.269, P<0.001) and 149±47 and 81±34 μm in the horizontal direction (t=5.132, P<0.001). There were statistically significant differences between the two groups in the central 1 mm range of CT, both vertically (t=4.386, P<0.001) and horizontally (t=4.468, P<0.001). There was a statistically significant difference in CT on the nasal side (t=4.747, P<0.001) in the 1-3 mm range of the vertical superior (t=4.836, P<0.001), inferior (t=4.452, P<0.001), horizontal temporal areas (t=4.001, P<0.001) and nasal (t=4.747, P<0.001). There was a statistically significant difference between the two groups in the 3-6 mm areas of the vertical superior (t=5.149, P<0.001) and inferior (t=5.390, P<0.001), and horizontal temporal (t=4.999, P<0.001) and nasal (t=5.646, P<0.001). At the same time, within the diameter of 6 mm, the vertical CVI between the 2 groups was 0.593±0.030 and 0.535±0.069, and the horizontal CVI was 0.595±0.025 and 0.545±0.073, respectively. Within the central 1 mm area, the CVIs in the vertical (Z=-2.353, P=0.019) and horizontal (t=3.109, P=0.004) directions were 0.595±0.025 and 0.545±0.073, respectively, and there was a statistically significant difference between the 2 groups. In the 1-3 mm range, there was a significant difference in CVI in the upper vertical direction (t=3.339, P=0.002) and in the horizontal nasal direction (Z=-2.029, P=0.042). In the upper vertical direction (Z=-3.111, P=0.002), there was a significant difference in CT on the nasal side (t=4.747, P<0.001). There was a statistically significant difference in CVI between the simple high myopia and pathological myopia groups in each region of the horizontal nasal side (Z=-2.083, P=0.037). The results of correlation analysis showed that CT and CVI decreased with an increase in the degree of myopia and an increase in the ocular axis.

Compared with high myopia, the CT and blood flow of pathological myopia show a significant decrease, and the changes have correlations with axial elongation and the decrease in spherical equivalent.

pathological myopia; swept-source optical coherence tomography; choroidal thickness; choroidal vascularity index