Macular Pigment Optical Density in Singapore Population

IntroductionMacular pigment (MP) is a yellow pigment found at the center of primate macula. It is believed to protect the macula against oxidative damage initiated by blue light and free radicals. Little is known if different ethnicity with same iris colour affects MP level and its distribution.Although Macular Metrics Densitometer (MMD) is a validated instrument to measure macular pigment optical density (MPOD), it must be operated by a trained personnel and the subject must clearly understand the task. In search of a better and faster instrument to measure MPOD, Macular Pigment Screener II (MPS II) was developed.This study aims to: (1) measure MP spatial profile (SP) in Singapore Chinese, Malay, and Indian using MMD; (2) compare MPOD obtained with MPS II and MMD. MethodsMP SP in 161 healthy volunteers, aged 21 to 63, were measured (72 Chinese, 47 Malay, and 42 Indian) in Khoo Teck Puat Hospital using MMD from 2013 to 2015. MPOD was also measured in 65 Chinese subjects at 0.50° retinal eccentricity using both MMD and MPS II on the same day. ResultsThe mean ± SD age of the study population is 30.6 ± 9.6, with 60 males and 101 females. Mean MPOD in the population at 0.50° retinal eccentricity was 0.58 ± 0.23, with the range 0.10 to 1.13. MPOD does not have any significant correlation with age (p = 0.15), gender (p = 0.15) and body mass index (BMI) (p = 0.32), except myopia (p = 0.02). There is no significant difference in MPOD with ethnicity (MPOD: Chinese = 0.57 ± 0.21; Malay = 0.60 ± 0.22; Indian = 0.59 ± 0.27, p = 0.73). Majority of the subjects have exponential MP SP (Malay = 78%, Chinese = 73%, Indian = 62%). Overall 22% to 38% of the subjects have atypical SP in form of central dip, secondary peak and plateau. There is a difference in MP SP among 3 ethnic groups (p = 0.05), when the plateau SP is excluded. Indian ethnicity demonstrated a higher number of atypical SP as secondary peaks at 1.00° retinal eccentricity. There is a good degree of correlation of MPOD between MPS II and MMD (MMD: 0.57 ± 0.21, MPS II: 0.48 ± 0.17; p <0.0001, R = 0.72).ConclusionThere is a significant difference in MP SP among the 3 ethnic groups, with Indian ethnicity demonstrating a higher number of atypical SP as secondary peaks. A larger sample size will be required to validate these observation in the future. MPS II is a good tool to screen MP, however, investigators need to be aware that MP readings are lower in MPS II compared to MMD.