Aim To evaluate racial differences, and ocular and systemic determinants of macular thickness (MT), measured by spectral-domain optical coherence tomography (SD-OCT) in a normal multiethnic Asian population.

Method MT was measured from a 6×6 mm² central macular area using the Cirrus high-definition OCT (HD-OCT) (Carl Zeiss Meditec, Dublin, CA). The associations between ocular and systemic factors with MT were evaluated using linear regression analyses with generalised estimating equation models to account for intereye correlation.

Results 7447 healthy eyes (2577 Chinese, 2072 Malays and 2798 Indians) of 4510 subjects were included. Multivariable analysis showed that older age (per decade, β=−4.39), female gender (β=−5.74), diabetes (β=−1.10), chronic kidney disease (CKD) (β=−3.21), longer axial length (per mm, β=−2.34), flatter corneal curvature (per mm, β=−1.79) and presence of cataract (β=−0.94) were associated with thinner overall average MT (OMT) (all p≤0.026); higher total cholesterol (β=0.44; p=0.010) was associated with thicker OMT. All these factors were also associated with thinner central subfield MT (CSMT) (all p≤0.001), except for cataract, total cholesterol and CKD. Meanwhile, longer axial length (β=2.51; p<0.001) was associated with thicker CSMT. OMT (mean±SD) was thickest in Chinese (279.9±12.5 µm), followed by Malays (276.5±13.7 µm) and Indians (272.4±13.1 µm), with p≤0.003 for all interethnic comparisons. Similar trend was observed for CSMT.

Conclusion There are interethnic differences in MT profile among Asians, particularly between Chinese and Indians. Ocular and systemic factors affect MT measurements as well. This Asian-specific information may be incorporated into existing clinical interpretation of macular OCT scans to aid in improving the diagnostic and monitoring accuracy of macular diseases among Asians.