Purpose: To estimate the heritability of the iridotrabecular angle width measured by anterior segment optical coherence tomography (ASOCT) in a classic twin study.

Methods: Twins aged 8 to 16 years were identified from the Guangzhou Twin Registry. ASOCT was used to obtain one horizontal scan, and the images were analyzed with custom software. Angle width was represented by the angle opening distance (AOD) at the 500-microm anterior-to-scleral spur, as well as the angle recess area (ARA) and trabecular-iris space area (TISA) located 750 microm anterior to the scleral spur. Zygosity was confirmed by genotyping with 16 polymorphic markers in all same-sex twin pairs. Heritability was assessed by structural variance component genetic modeling after adjustment for age and sex, with the Mx program.

Results: The mean age of the participants was 11.7 +/- 2.6 years in 305 monozygotic (MZ) and 11.8 +/- 2.4 years in 157 dizygotic (DZ) pairs. The intraclass correlation coefficients for the AOD, ARA, and TISA were 0.70, 0.75, and 0.72 in the MZ pairs and 0.34, 0.32, and 0.33 in the DZ pairs, respectively. A model with additive genetic (69.7%; 95% CI: 63.9%-74.6%) and unique environmental effects (30.3%; 95% CI: 25.4%-36.1%) was the most parsimonious for AOD. Similar results were identified for ARA and TISA.

Conclusions: The variance in drainage angle width in Chinese children appears to be largely attributable to genetic effects, with a heritability of approximately 70%.