Assessment of iris pigment epithelium depolarization and associated factors using polarization-sensitive anterior segment optical coherence tomography

Purpose: To assess the distribution of depolarization and its association with demographic and ocular biometric factors, we used polarization-sensitive anterior segment optical coherence tomography (PS-AS-OCT), to investigate the characteristics of the iris pigment epithelium (IPE) in healthy eyes. Method: A group of 105 healthy Japanese adults participated in this study, and PS-AS-OCT images were captured for both eyes. The IPE depolarization region was segmented from the horizontal scan of the left eye images. The measurement of depolarization was determined by assessing two parameters: the height of the IPE depolarization region in the grayscale entropy image and the melanin concentration rate in the color entropy image. To investigate the distribution of depolarization, the segmented region was evenly divided into 99 fractions. This division was then evaluated at various locations within the IPE depolarization region using the depolarization parameters. Subsequantly, we analyzed the values obtained in relation to demographic and ocular biometric factors. Such factors include age, gender, axial length (AL), anterior chamber depth (ACD), central corneal thickness (CCT), and lens thickness (LT). Results: A total of 105 patients (age 39 ± 11yrs) fulfilled the inclusion criteria, including 84 males and 21 females. The height of the IPE depolarization region increased in both the pupillary and peripheral regions, while it remained stable in the midzone region. The distribution of melanin concentration rate exhibited a smooth pattern, with a decrease observed only in the periphery. Furthermore, the height of IPE depolarization in the peripheral region was found to be negatively correlated with AL and ACD, but positively correlated with LT, while the melanin concentration rate of specific points in mid-peripheral region was negatively correlated with AL (P < 0.05). Conclusion: By observing the distribution of IPE melanin-related depolarization in vivo though PS-AS-OCT, we identified the association between depolarization parameters and biometric factors AL, ACD and LT. This comprehensive baseline of the IPE depolarization parameters in healthy Japanese adults may offer valuable insights, especially in the context of pathological conditions.