Glaucoma Dialogue IGR 12-1


Ningli Wang

Comment by Ningli Wang on:

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

See also comment(s) by David FriedmanJian GePaul HealeyJost JonasRobert RitchPhilippe Denis & Florent Aptel

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There are two stated objectives of this cross-sectional study. The first was to describe and validate a method for estimating iris volume using anterior segment optical coherence tomography (ASOCT). The second was to study and quantify changes in iris volume induced by pharmacologic mydriasis in patients with narrow angles and patent iridotomy and in age and gender-matched controls with open angles. The authors concluded that their research provides novel evidence on the importance of iris dynamics in angle-closure pathogenesis and successfully evaluates iris volume changes with ASOCT. However, without actually discussing a non-pupillary block mechanism in this elderly patient sample (table 1), merely implicating iris dynamics as a cause of angle closure is a limitation of the study.

Angle narrowing or closure also may occur after pupillary block has been eliminated in eyes with narrow angles that have a patent laser peripheral iridotomy, usually on the basis of plateau iris or lens related angle closure. It would have been interesting, given a mean patient age of 72.4 years, if the authors had commented on the characteristics of the lens and mentioned the change in IOP with dilation, since almost seven of the 30 patients enrolled needed medical management to control IOP.

Compared to previous studies which concluded that there is a change in iris volume if there is a change in cross sectional area, Aptel et al calculated the volume change by measuring both the area and the distance from the axis of symmetry and the center of mass of the cross sectional area. The advantage of this method is that we can calculate the volume from the area and radius that are both available from the OCT images. The authors have also used three equations, including one using eight partial volume measurements, adding more accuracy to their volume calculation.

In conclusion, this appears to be a fairly straightforward study with reasonable conclusions. However, the strength of this study would have been better served if the authors had taken their analysis a step further and expanded on iris dynamics to evaluate physiologic mydriasis within different illumination settings. The authors also could have examined other quantitative parameters, including anterior chamber volume changes in the face of fluid shifts within the iris stroma, non-pupillary block mechanisms of angle-closure, and iris configuration. Further longitudinal studies are needed to answer the questions of why the iris moves anteriorly if there is an increase in its volume and why PAS occur more frequently in the superior quadrant if there is a uniform increase in iris volume in patients before and after laser peripheral iridotomy.

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