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C. Y. Cheung, S. Kumar, H. Li, C. P. Pang, R. Ritch, D. S. C. Lam, C. K. Leung; Dynamic Analysis of Iris Convexity With Anterior Segment Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5433. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the dynamic changes of iris convexity and its relation to the anterior chamber angle using the anterior segment optical coherence tomography (OCT).
Thirty-seven normal subjects with open angles on dark room gonioscopy and 18 subjects with narrow angles were analyzed. The dynamic dark-light changes of the anterior chamber angle and iris convexity were captured with real-time video recording. The trabecular iris space area (TISA500), the iris convexity (measured as the vertical distance from the iris base perpendicular to a line joining the iris tip and iris root) of the nasal angle, and the pupil diameter were measured in serial frames selected from video capture. Linear regression analysis was performed to investigate the association between TISA500 / iris convexity and pupil diameter. The associations between iris convexity difference [iris convexity (dark) - (light)], TISA difference (TISA500 (light)-(dark)), axial length, age and TISA500 measured in the dark were evaluated with multivariate regression analysis.
The iris convexity / TISA500 measured in the light in the open angle and the narrow angle groups were -0.35mm / 0.24 ± 0.10mm2 and 6.26mm / 0.10 ± 0.03mm2, respectively. These values were significantly different than the iris convexity / TISA500 measured in the dark (3.54mm / 0.16 ± 0.08mm2 and 13.07mm / 0.05 ± 0.04mm2, respectively, all with p<0.001). The slopes of the linear regression between iris convexity / TISA and pupil size were significantly correlated with gonioscopy grade of the angle (p=0.007 and 0.039, respectively). The difference of iris convexity was higher in the narrow angle compared with that in the open angle groups (p=0.001). Axial length (standardized coefficient β = 0.473, p<0.001), age (β = -0.297, p=0.029), and iris convexity difference (β = -0.250, p=0.018) are independent predictors for TISA measured in the dark (R2=0.532).
Independent to axial length and age, change in iris convexity is an important factor contributing to narrowing of the anterior chamber angle. Investigating the structure and dynamics of iris configuration may enhance our understanding of the mechanism of angle closure glaucoma.
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