Characterization of the depolarization contrast line in the outer retina using polarization-sensitive optical coherence tomography

This study aimed to characterize the anatomical features of a new observation, the depolarization contrast line (DCL) near the photoreceptor inner/outer segment (IS/OS) area visualized using polarization-sensitive optical coherence tomography (PS-OCT). Twenty-eight participants (56 eyes) with no fundus disease were included. Horizontal and vertical B-scan images, averaged from 100 frames passing through the fovea, were analyzed using polarimetric entropy, a dimensionless parameter reflecting depolarization. The mean entropy at the DCL was 0.191 ± 0.043, with a correlation between horizontal and vertical directions (R² = 0.577, p < 0.0001) and between the right and left eyes (R² = 0.240, p = 0.046). In 25 eyes with good image quality, entropy showed a negative correlation with age (R² = 0.217, p = 0.019). In 11 eyes analyzed with a distinct DCL, this line was consistently located between the external limiting membrane (ELM) and the ellipsoid zone on the intensity OCT image, positioned at 80.0% of the distance from the retinal pigment epithelium toward ELM at the fovea, 86.4% at 1 mm nasal, and 85.8% at 1 mm temporal. These findings suggest that the DCL corresponds to structural components within the photoreceptor inner segments, providing insights into photoreceptor structural organization.