Abstract
Purpose :
Melanin naturally presents in the eye including the iris, retinal pigment epithelium, and choroid. The concentration of the melanin changes with aging1. Polarization-sensitive OCT (PS-OCT) enables the measurement of the degree of depolarization (DOP) of the eye. Recent studies have shown that DOP is a feasible way to measure the melanin in animals2 and human3. However, the DOP signal is highly correlated with the light intensity4. In this study, we developed an ad-hoc calibration method to decouple the DOP and intensity in a customized PS-OCT. In a guinea pig model, we longitudinally measured the DOP and estimated the melanin distribution in a guinea pig model for 8 weeks in vivo.
Methods :
To mitigate the correlation between image intensity and DOP, we fitted an empirical function between SNR and DOP with measured data from an Albino eye (Fig. 1a), assuming no physical depolarization induced by pigmentation. The calibrated DOP was obtained by subtracting the original DOP from the reference DOP in the SNR-DOP function. A total of 10 eyes from 5 guinea pigs (4 pigmented; 1 albino) were imaged weekly with a PS-OCT for 8 weeks. We evaluated the difference of DOP signals associating with pigmentation, ages, and individuals.
Results :
We found that the SNR-DOP empirical function was consistent in different datasets from different albino animals (Fig. 1a). After applying the calibration, the DOP contrast was better in agreement with the distribution of melanin, mainly concentrated in the choroid, (Fig. 1b 1c). We quantified calibrated DOP in retinal volume scans (Fig. 2i 2ii) and found it was increasing in pigmented eyes with age (Fig. 2iii).
Conclusions :
In this study, we demonstrated that the DOP from a PS-OCT could be calibrated to present better contrast of pigmentation in the eye. We observed the DOP was increasing with age in young pigmented guinea pigs, revealing that melanin accumulated in the choroid.
This is a 2021 ARVO Annual Meeting abstract.