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Editors Selection IGR 23-3

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Comment by Jost Jonas on:

25131 Optical coherence tomography quantitative analysis of iris volume changes after pharmacologic mydriasis, Aptel F; Denis P, Ophthalmology, 2010; 117: 3-10

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Is iris volume change upon dilatation a key mechanism of angle closure? This has been proposed by Quigley et al., who reported a smaller decrease in iris cross-sectional area in eyes with angle closure compared to open-angle glaucoma after mydriasis (J Glaucoma 2009; 18: 3). Aptel and Denis repeated this study, but used four cross-sectional AS-OCT images to estimate iris volume. They compared the effect of pharmacological mydriasis on changes in iris volume between fellows of eyes with prior acutely symptomatic angle closure (AAC) and controls presenting to the same clinic for refraction. While cross-sectional iris area decreased in both groups, and volume decreased in controls, iris volume increased in almost all of the patients with AAC. As iris volume is simply iris cross-sectional area rotated 360 degrees, this finding is rather surprising. It appears to be due to the slightly smaller pupil size prior to dilation and the significantly larger pupil size after dilation in the AAC group, thereby increasing the radius through which the volume is calculated. As is common, there were many other differences between cases and controls including refraction (the control group was a little myopic), axial length, anterior chamber depth, and, of course anatomical angle configuration. We do not know the ethnicity of cases (Quigley found Europeans have smaller iris cross-sectional areas) or whether they differed from controls. We also do not know whether the iris changes found in the cases were predictors of AC or were rather a characteristic of smaller eyes with narrower angles. This is important because anatomically narrow angles are very common in many parts of Asia where AC rates are highest. We await with interest a repetition of this study in an Asian population where eyes with AC are compared to controls with anatomically narrow angles without AC.

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