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Editors Selection IGR 10-2

Angle Closure: Iris histology

Comment by Ian Grierson on:

21875 Histologic changes of the iris in the development of angle closure in Chinese eyes, He M; Lu Y; Liu X et al., Journal of Glaucoma, 2008; 17: 386-392

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There is evidence to suggest that in China alone the numbers of people with shallow anterior chamber angles potentially at risk of angle closure is nearly 30 million. That only 20% or less actually go on to angle closure, at least within a period of a few years, suggests additional factors are important. Of these, the He et al. (IGR 10-3: 1114) consider that the biomechanical characteristics of the iris itself need to be taken into account. It is the case that little morphologic work has been done on the iris of angle closure patients and so the authors conducted a semi-quantative analysis of the extracellular matrix of the iris stroma by light microscopy and additional qualitative investigation of the tissue by electron microscopy. Consecutive, newly diagnosed glaucoma patients for whom surgery was indicated provided the iridectomy specimens and included acute angle closure, fellow eyes of acute closures, suspect angle closures, chronic closures and open angle patients. The specimens were all from one surgeon. The histopathology concentrated on the abundance of collagen type I highlighted by Sirus red staining and showed by masked grading-type of analysis significantly higher amounts of this collagen in the iris stroma of acute angle closure than in controls whereas chronic closure patients had less. The authors advance the idea that more collagen I equates to less iris elasticity so possibly predisposing these eyes with stiffer irides to prolonged and more extensive contact during angle closure. It is a novel study and an interesting possible relationship but as yet essentially speculative. The authors are fully aware of the analytical limitations associated with necessarily small and therefore potentially unrepresentative specimens. It is unfortunate, given the importance of grading collagen staining accurately and reproducibly, that only one masked observer was used as grader so no inter observer error could be calculated.

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