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Editors Selection IGR 17-4

Angle-closure glaucoma: Gonioscopy versus AS-OCT

Comment by Celso Tello & Pat-Michael Palmiero on:

20981 Comparison of gonioscopy and anterior segment ocular coherence tomography in detecting angle closure in different quadrants of the anterior chamber angle, Sakata LM; Lavanya R; Friedman DS et al., Ophthalmology, 2008; 115: 769-774

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To date, darkroom gonioscopy remains the gold standard in evaluating the anterior chamber angle (ACA). Anterior segment optical coherence tomography (AS-OCT) imaging provides quantitative information on anterior segment dimensions, angle configuration and its biometric parameters. It has been used to study changes in the ACA under various conditions such as in provocative testing and after laser treatment.^1-3 In their large cross-sectional observational study, Sakata et al. (611) compared the performance of gonioscopy and AS-OCT in detecting angle closure in the different quadrants of the ACA in a cohort of 502 patients with no prior ophthalmic problems and found a closed angle in at least one quadrant in 59% of the eyes by AS-OCT and in 33% of the eyes by gonioscopy (p < 0.001), with fair agreement between the two methods (κ = 0.40). Using both techniques they concluded that the highest rate of closed angles was in the superior quadrant. They also concluded that AS-OCT tended to detect more closed angles than gonioscopy and believed this was caused by variations in the iris profile and level of iridocorneal contact. The authors' findings agree with previous reports where the superior quadrant was narrowest and increased detection of angle closure was found using AS-OCT compared to gonioscopy (71% vs. 49.5%, respectively).^4,5 We believe further prospective studies are warranted to analyze the variations in iris profile and level of iridocorneal contact described by Sakata et al. These differences may be due to anatomic entities related to angle closure such as anterior iris/lens insertion or plateau iris configuration. We also be-lieve that the angle configuration may be indirectly affected by the amount of illumination used during examinations, and it should be taken in account when comparing these two techniques. The largest disparity between the two techniques occurred in the superior and inferior quadrants. This may be related to the technical difficulties (e.g., small palpebral fissures) in obtaining AS-OCT imaging in the superior and inferior quadrants. Indentation gonioscopy may have also led to disagreement in the results. The cutoff for gonioscopic grading in angle closure was done using the Scheie grading system. We believe the results may differ if another gonioscopic grading sys-tem is used such as the Schaffer grading system, where the angle is divided to open, narrow, slit, and closed. In conclusion, this is an interesting study that aimed to compare AS-OCT and gonioscopy in diagnosing angle closure. In the era of advanced technology, additional prospective studies are necessary to aid in understanding the discrepancy between gonioscopy and imaging techniques.

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