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Editors Selection IGR 16-3
Clinical Forms of Glaucoma: Iris thickness in PACG
Comment by Ningli Wang on:
27841 Increased iris thickness and association with primary angle closure glaucoma, Wang B-S; Narayanaswamy A; Amerasinghe N et al., British Journal of Ophthalmology, 2011; 95: 46-50
A recent paper by Wang et al. (36) reported that increased iris thickness is associated with angle closure. After adjusting for age, sex, pupil size and anterior chamber depth, mean iris thickness at 750 um and 2000 um from the sclera spur, maximal iris thickness and cross-sectional area of the iris were significantly greater in angleclosure eyes versus normal eyes. The results of the current study nicely confirmed their previous findings and conclusion.1
These findings suggest iris thickness may play an important role in the etiology of primary angle-closure glaucoma (PACG). In a laboratory model that simulated the anterior segment structures with artificial materials, doubling the iris thickness can increase the posterior to anterior pressure differential. This supports the hypothesis that a thick iris increases pressure differential between the posterior chamber and anterior chamber, causing the peripheral iris to bow forwards and block the trabecular meshwork.2
However, cross-sectional study of known anatomic factors in angleclosure eyes cannot fully explain the etiology ofPACG. To my point, the risk factors for PACG are family history, female gender, increasing age, ethnicity (especially in Chinese, Mongolians, Indian and Eskimos/ Intuits), shallow anterior chamber and shorter axial length. Genetic factors may also contribute to the developing of PACG. It is notable that the genetic locus for PACG has not been published and genome-wide scan studies have not been identified that contribute to the PACG. Increased emphasis should be placed on the genetic study of PACG. Recently, Aptel's study shows that the iris volume increases after pupil dilation in narrow-angle eyes predisposed to acute angle closure.3 Combination of dynamic changes of iris and other known static anatomic parameters may help us better understand the mechanism of PACG.
References
- Wang BS, Sakata LM, Friedman DS, et al. Quantitative iris parameters and association with narrow angles. Ophthalmology 2010;117:11e17.
- Wyatt H, Ghosh J. Behaviour of an iris model and the pupil block hypothesis. Br J Ophthalmol. 1970;54:177-185)
- Aptel F, Denis P. Optical Coherence Tomography Quantitative Analysis of Iris Volume Changes after Pharmacologic Mydriasis, 2010,117(1)3-10
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