Abstract
Purpose :
Although the depolarization of iris pigment epithelium (IPE) is one characteristic property in polarization-sensitive optical coherence tomography (PS-OCT) images of the anterior eye segment, it received limited attention and has not been investigated to date. This study aims at exploring quantification standards to assess potential properties of the quasi-IPE region in PS-OCT images.
Methods :
This cross-sectional, observational study is based on PS-OCT images from 101 healthy eyes observed under identical environment and machine setting. For the quantitative analysis of depolarization in IPE, we use depolarization metric polarimetric entropy that is known to be associated with density of melanin granules. Three PS-OCT images (intensity, grey-scale entropy, and false-colored entropy) at horizontal cross-section of each eye are shown in Fig. 1.
Scleral Spur (SS) is identified using custom-developed model on the intensity image. The highlighted area under iris is manually segmented from grey-scale entropy images as quasi-IPE region. Thickness of the quasi-IPE is measured at a distance of 2000μm from the SS and defined as T2000. The area of the quasi-IPE is defined as IPE-Area. Melanin concentration rate 0.5(MCR0.5) is defined as a ratio of the entropy over 0.5 compared to the total area in IPE-Area. For each variable, differences in gender and age groups were analyzed through student t-test or one-way ANOVA at its temporal or nasal regions separately.
Results :
The 101 participants included 79 male and 22 female with mean age of 39.0±11.3yrs, ranging from 18-64yrs. Among the three quantification values, IPE-Area (averages at temporal or nasal (T/N): 1.52±0.25 or 1.34±0.24 mm2) showed significant difference between gender groups. (T/N: p=0.010 or 0.016). While T2000(T/N: 0.27±0.03mm or 0.27±0.04 mm) and MCR0.5 (T/N: 0.79±0.065 or 0.81±0.04.9) were not significant in both age and gender groups.
Conclusions :
Quantitative results suggest a stable structural region under the iris. The quasi-IPE structure that has high depolarization might be a combination of melanin concentrated IPE layer and fuzzy area caused by scattering of light by melanin granules.
To the best of our knowledge, this is the first attempt made on quantification of the quasi-IPE region in PS-OCT images. Future work may involve laboratorial examinations on diseased eyes or anatomy-based research.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.