Sectoral variations of iridocorneal angle width and iris volume in Chinese Singaporeans: a swept-source optical coherence tomography study

PurposeTo assess variations in the iridocorneal angle width and iris volume in Chinese subjects using swept-source optical coherence tomography (SS-OCT).MethodsConsecutive subjects, aged 40–80 years, with no previous ophthalmic problems were recruited from a population-based study of Chinese Singaporeans. All subjects underwent 360° SS-OCT (SS-1000 CASIA, Tomey Corporation, Nagoya, Japan) angle imaging and gonioscopy in one randomly selected eye in the dark. For each eye, 16 frames (11.25° apart) were selected for analysis from 128 cross-sectional images, and measurements of the trabecular iris space area 750 μm from the scleral spur (TISA750) and iris volume were made for each image. The measurements from four consecutive frames were further averaged as a sector of 45°. Sector-wise angle width and quadrant-wise iris volume were analyzed.ResultsTwo hundred and twelve subjects (90 with closed-angles) were examined. The majority of the subjects were female (70.7 %) with mean age 61 (±8.9) years. The TISA750 (mm2) of superior [0.101 (0.09)], inferior [0.105 (0.09)], superior–nasal [0.111 (0.09)] and superior–temporal [0.117 (0.09)] sectors were smaller compared with other sectors (P < 0.05). The nasal iris volume (mm3) was the smallest compared with other quadrants for the entire cohort [nasal 8.18 (1.2) < inferior 9.13 (1.3) < temporal 9.16 (1.2) < superior 9.33 (1.3), P < 0.001], as well as for open- and closed-angle groups.ConclusionsThe irido-corneal angle was narrower in the superior, inferior, superior–nasal and superior–temporal sectors compared with other sectors. Iris volume in the nasal quadrant was the smallest compared with the other quadrants.

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