Purpose

To examine the normative profile and determinants of macular ganglion cell-inner plexiform layer (GCIPL) thickness based on spectral-domain OCT (SD-OCT) in a nonglaucoma, multi-ethnic Asian population.

Design

Population-based, cross-sectional study.

Participants

Ethnic Chinese, Malay, and Indian adults aged ≥40 years recruited from the Singapore Epidemiology of Eye Diseases Study.

Methods

All participants underwent standardized examinations. The GCIPL thickness was measured using Cirrus HD-OCT (Carl Zeiss Meditec, Dublin, CA). Participants with glaucoma or poor-quality scans were excluded. Eye-specific data were used. Associations of ocular and systemic factors with GCIPL thickness parameters were investigated using multivariable linear regression with generalized estimating equation models to account for correlation between both eyes.

Main Outcome Measures

GCIPL thickness.

Results

A total of 4464 participants (7520 eyes) consisting of 1625 Chinese, 1212 Malay, and 1627 Indian adults contributed to this analysis. Average GCIPL thickness was 82.6±6.1 μm in Chinese, 81.5±6.8 μm in Malays, and 78.0±6.9 μm in Indians (P < 0.001 by analysis of variance). The 5th percentile limit of average GCIPL thickness was 72 μm in Chinese, 70 μm in Malays, and 67 μm in Indians. In multivariable analysis adjusting for age, gender, axial length, presence of cataract, OCT signal strength, disc area, hypertension, diabetes, and hyperlipidemia, eyes of Indians were observed to have 3.43 μm thinner GCIPL on average compared with Chinese (P < 0.001) and 3.36 μm thinner GCIPL compared with Malays (P < 0.001). In addition, older age (per decade; β = −2.51), female (β = −1.57), longer axial length (per mm; β = −1.54), and presence of chronic kidney disease (β = −1.49) were significantly associated with thinner average GCIPL (all P ≤ 0.008). Larger optic disc area (per mm²; β = 0.78; P < 0.001) was associated with thicker GCIPL. These factors were consistently observed to be significant for superior and inferior hemisphere GCIPL thickness.

Conclusions

GCIPL thickness profiles were significantly thinner in Indians compared with Chinese and Malays. Our findings further highlight the need of a more refined, ethnic-specific normative database for GCIPL thickness, which in turn may improve the detection and diagnosis of glaucoma in Asians.