Vascular Changes of the Choroid and Their Correlations With Visual Acuity in Pathological Myopia.

Purpose: Photoreceptor loss plays a role in visual impairment in pathological myopia. As the nutrition and oxygen demands of photoreceptors are mainly supported by the choroidal vessels, we aimed to investigate changes in the choroidal vasculature and their correlations with visual acuity in pathological myopia.
Methods: The cohort was composed of 136 eyes from 80 participants, including 42 eyes from 21 participants with emmetropia/low myopia, 48 eyes from 26 participants with simple high myopia, and 46 eyes from 33 participants with pathological myopia. Swept-source optical coherence tomography (OCT) was used to image the eyes with a 12-mm radial line scan protocol. The parameters for 6-mm diameters of macula area centered on the fovea were analyzed. A custom deep learning algorithm based on a modified residual U-Net architecture was used to segment the choroidal boundaries. Then, the distance between the two boundaries was determined and choroidal thickness (CT), luminal area (LA), and stromal area (SA) were demarcated based on Niblack's auto-local threshold algorithm after binarization of the OCT images. Finally, the ratio of LA and total choroidal area was defined as the choroidal vascularity index (CVI). The choroidal parameters in three groups were compared, and correlations of the choroidal parameters with age, gender, axial length, and best-corrected visual acuity (BCVA) were analyzed.
Results: The CVI, CT, LA, and SA values were lower in pathological myopia than in emmetropia/low myopia and simple high myopia (P < 0.05). The CT, LA, and SA values were lower in simple high myopia than in emmetropia/low myopia (P < 0.05), whereas there was no difference between the CVIs in the emmetropia/low myopia and high myopia groups (P > 0.05). The CVI was nonlinear with increases in axial length (AL), and there was a critical AL flexion point, approximately 27.26 mm; however, the CT, LA, and SA were negatively correlated with AL. Further analysis showed that only younger subjects (40 years old or less) showed significant AL flexion points. Simple and multiple regression models showed that the CVI was correlated with BCVA (P < 0.05).
Conclusions: Choroidal vascular alterations, especially decreased CVI, occurred in patients with pathological myopia. The CVI decreased with axial elongation beyond the flexion point and was correlated with visual impairment, indicating that the CVI might be a reliable imaging biomarker to monitor the progression of pathological myopia.