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Editors Selection IGR 21-4

Surgical treatment: Prophylactic Iridotomy in Angle-Closure suspects

Comment by Robert Feldman 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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Anterior segment optical coherence tomography (ASOCT) is becoming an increasingly valuable tool with which to evaluate the anterior segment. ASOCT provides high resolution images of the anterior segment from which quantitative information about the angle can be derived. While gonioscopy is still an invaluable examination tool, ASOCT offers new opportunities to evaluate how anatomy is related to anterior segment disease.

The spectrum of primary angle closure (PAC) disease (including primary angle closure suspects [PACS], PAC, and primary angle closure glaucoma [PACG]) is precipitated by changes in anterior segment anatomy. Iris anatomy and configuration is an important facet of the disease process and severity, and thicker irides have been suggested to be associated with angle closure. However, characterization of and the role the iris plays in the disease mechanism has not yet fully been elucidated.

The goal of Lee et al.'s study was to determine if there was an association between baseline iris parameters and a change in the iris anatomy after laser peripheral iridotomy (LPI). ASOCT images were obtained from 52 White and Chinese PACS patients before and after LPI. Iris thickness, curvature, and trabecular-iris space area (TISA) at 500 μm (TISA500) and 750 μm (TISA750) from the scleral spur were evaluated. They found that lower baseline iris thickness was associated with a decrease in iris curvature and an increase in TISA after LPI, meaning thinner irides were more likely to exhibit a greater flattening and opening of the angle with LPI.

While the results of this study are important and a crucial start to examining the role of the iris in angle closure, there are limitations. Data was only analyzed with images from the nasal quadrant, which limits extrapolation of this data to the entire angle circumference. This was due to limitations of the ASOCT technology employed in this study (1 meridian was imaged). Newer technology, such as with Tomey's CASIA SS-1000 (Nagoya, Japan) can now image 128 meridians (256 angles, or every 1.4 degrees) and provide three dimensional reconstruction, which can provide information about the entire peripheral angle. However, this study does demonstrate the anatomic efficacy of LPI and presents a possible factor for quantitating efficacy.

Further study into the dynamics of the iris with treatment is important to unlocking the mechanism of this disease and in monitoring continued efficacy of treatment

Further study into the dynamics of the iris with treatment is important to unlocking the mechanism of this disease and in monitoring continued efficacy of treatment.

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