Our finding that AOD750 was a major correlate of I-Curv has not been reported previously to our knowledge. AOD750 was shown previously to have a high discriminative ability for identifying the presence of narrow angles on gonioscopy.
30 A community-based study that included 2047 Singaporean subjects > 50 years old showed that increased I-Curv, I-Area, and IT750 were associated significantly with narrow angles (odds ratio [OR] 2.5 and 95% CI 1.3–5.1, OR 2.7 and 95% CI 1.6–4.8, and OR 2.6 and 95% CI 1.6–4.1, respectively, comparing fourth with first quartile for each parameter) after adjusting for age, sex, ACD, AL, and pupil size.
21 In our study, AOD750 accounted for nearly half of the variation in I-Curv, supporting the hypothesis that angle width and the extent of pupil block are highly correlated, as I-Curv can be regarded as a surrogate measure of pupil block. Pupil block creates a pressure differential between the anterior and posterior chambers, which causes the iris to adopt a convex forward bowing configuration, and this results in a narrow or closed angle.
1–5,31 In contrast, AOD750 only explained 5.9% of the variation in IT750 and 3.0% of the variation in I-Area. These findings are consistent with an earlier study by Wang et al., which compared 167 participants with angle closure and 1153 normal participants, and reported that larger IT750 was associated with a small, but significant increase in the risk of angle closure (multivariate-adjusted OR 1.7, 95% CI 1.1–2.7,
P = 0.032, per 0.1 unit increase), while I-Area was not associated independently with angle closure, after adjusting for age, sex, pupil size, and ACD.
12 A thicker peripheral iris would contribute to angle crowding and subsequent angle closure as the peripheral iris would be in closer proximity with the trabecular meshwork. However, IT750 was not found to be an independent determinant of AOD750 or TISA750 in an optimal model determined by a stepwise selection algorithm. In contrast, other anterior segment parameters are much more important determinants of AOD750 and TISA750.
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