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Editors Selection IGR 24-3

Surgical treatment: Prophylactic Iridotomy in Angle-Closure suspects

Comment by Tin Aung & Mani Baskaran on:

56868 Association between baseline iris thickness and prophylactic laser peripheral iridotomy outcomes in primary angle-closure suspects, Lee RY; Kasuga T; Cui QN et al., Ophthalmology, 2014; 121: 1194-1202

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In this paper, Lee et al.¹ evaluated the association of iris thickness (IT at 750 microns and 2000 microns) using anterior segment optical coherence tomography (ASOCT) before laser peripheral iridotomy (LPI) with angle widening (as assessed by trabecular iris-space area -TISA at 500 and 750 microns from the scleral spur) after laser peripheral iridotomy (LPI). The study was conducted on 52 hospital-based primary angle closure suspect (PACS) patients of Caucasian and Chinese ethnicity. They found that a thinner iris was predictive of wider angle width after LPI, after adjusting for age, gender and pupil diameter. These findings may have implications in predicting which angle closure patients will respond well to LPI.

This study used a simple model and did not consider the influence of lens factors such as the lens vault, or intraocular pressure, which are important components of the anterior chamber milieu that determines angle width and the pressure difference between the anterior and posterior chambers.² The sample size was small and of mixed ethnicity. Iris thickness is a dynamic factor, however, only static measures were collected in the study.

An earlier study in a larger sample of Chinese subjects found contradictory findings,² namely a thicker iris (as measured by iris thickness at 2000 microns) was associated with greater change in angle width, after adjusting for other factors such as lens vault, anterior chamber width, axial length and intraocular pressure.

Factors related to how the images were obtained may have influenced the difference in findings. The posterior limit of the iris is generally imaged poorly with ASOCT, and the iris measurements can be prone to errors due to poor delineation of the posterior pigmented layer. The extent of angle widening after LPI may differ between light and dark conditions, and according to the position of iris insertion.³

Further work is suggested using the three-dimensional scans available with swept source anterior segment OCT

Further work is suggested using the three-dimensional scans available with swept source anterior segment OCT, which by utilizing iris and angle data over 360°, may be more accurate and have lower variability compared to ASOCT.

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