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Comment by Robert Ritch 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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Aptel and Denis report a new method using anterior segment optical coherence tomography (ASOCT) for estimating iris volume. For the first time, they report that iris volume increases after pupil dilation in most narrow-angle eyes predisposed to angle closure compared with open-angle eyes.

In this study, seven of the 30 fellow eyes required intraocular pressure- lowering treatment after dilation. We presume that iris volume of these seven subjects increased by the congestion of iris circulation due to ocular hypertension or the exudation from iris vessels and this may affect the overall mean values. Besides, one also can speculate that iris thickness may be affected by the diameter of iris vessels, thus different sympathetic nerve activity of iris vessels to the pharmacologic mydriasis may also affect the iris thickness. Primary angle-closure suspect (PACS) with shallower anterior chamber depth and thicker lenses are known to have greater angle-closure risk. However, who will develop PAC may reside in the dynamic responses of the eye, not simply in their static anatomy. Three years ago, the clinical utility of of using ASOCT to measure anterior chamber volume (ACV) was reported. It was observed that LPI leads to increase in ACV in PAC patients.¹ The main results of the study by Aptel and Denis nicely revealed that iris volume is another potential biometric value to identify the high risk primary angle closure suspect. Iris volume may present with different responses to illumination or pharmacologic mydriasis because of the heterogeneous structure of the dilator. Furthermore, iris cross-sectional area and iris volume changes in the accommodated and unaccommodated states may also help us to investigate the dynamic changes of the iris dilator and sphincter muscles.

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