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Editors Selection IGR 16-4
Risk Factors for Glaucoma: Angle-closure
Comment by Syril Dorairaj on:
55326 Development of a score and probability estimate for detecting angle closure based on anterior segment optical coherence tomography, Nongpiur ME; Haaland BA; Perera SA et al., American Journal of Ophthalmology, 2014; 157: 32-38.e1
This cross-sectional study primarily aims to develop an angle closure score and probability estimate to objectively diagnose angle closure based on anterior segment optical coherence tomography (AS OCT). The statistically derived score is based on six parameters measured by AS OCT, previously found to give the most accurate and reliable algorithm to detect gonioscopic angle closure: anterior chamber (AC) volume, width, and area; iris thickness and area; and lens vault. With probability threshold set to 0.5, diagnosis of angle closure using the algorithm has a specificity of 0.96 and sensitivity of 0.75.
The secondary purpose of the study is to identify the anatomic structures imaged by AS OCT that may contribute to angle closure. Of the 1368 participants included, 90% were Chinese, and 295 participants (21.6%) were found to have angle closure on dark room gonioscopy. These participants were older, had shallower AC depth, and smaller AC width, area, and volume; they also had thicker irides and greater lens vault.
The main limitation of the first purpose of the study is the customized, semi-automated image analysis software (Zhongshan Angle Assessment Program) that requires manual detection of the location of the scleral spur. 22.8% of the participants were excluded because the scleral spur was not identifiable on AS OCT images, and 2.1% were excluded because of software delineation errors. This elimination makes the software's utility as a screening tool questionable since nearly one quarter of the population would be excluded. It should also be noted that visibility of scleral spur and angle width varies with quadrant analyzed, and iris configuration varies with time, accommodation, and illumination and directly alters the biometric parameters evaluated.
As far as identifying the anatomic structures that contribute to angle closure, It is well-documented that plateau iris is a major cause of angle closure, particularly in patients of Asian origin. It is known that the plateau configuration cannot be visualized using AS OCT as the posterior iris epithelium prevents passage of light past the iris. However, similar studies in the future correlating indentation gonioscopy with iris configuration and lens vault might give indirect information on plateau iris configuration on ASOCT images.
Despite this drawback, this study has taken an important step in developing a more objective, non-invasive method to reliably diagnose angle closure by using a score and probability estimate derived from parameters measured by AS OCT. Future studies with more advanced, fully automated software will likely propel AS OCT as a useful, non-invasive diagnostic tool for identifying angle closure, which would be especially useful in areas with a high prevalence of disease. However, dark room indentation gonioscopy still remains an important part of our examination to detect angle closure.
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