Various factors can result in discordance between gonioscopy and Anterior Segment Optical Coherence Tomography (AS-OCT) when assessing angle closure

The Science behind the Tip

Gonioscopy remains the gold standard for confirming iridotrabecular contact and diagnosing angle closure.1 AS-OCT and gonioscopy utilise different definitions of angle closure meaning that discordance in ascribing an angle as closed may simply be due to differences in definition. Accurate localization of the scleral spur landmark is critical to AS-OCT interpretation.2

Gonioscopy can falsely classify closed angles as open due to the effect of light on the pupil and inadvertent corneal indentation. Although AS-OCT will detect most eyes showing a closed angle on gonioscopy (high sensitivity)3, AS-OCT will detect a closed angle in more eyes when compared with gonioscopy (lower specificity), particularly in superior and inferior quadrants.4 In quadrants with a steep iris profile, the angle is more likely to be classified as closed on gonioscopy than with AS-OCT, while in quadrants with short iridoangle contact the discordance is reversed.5 In conclusion, AS-OCT is a complementary examination that should not replace gonioscopy in clinical practice.

References

1. EGS Guidelines, 5th Edition. https://eugs.org/educational_materials/6
2. Bourne RR, Zhekov I, Pardhan S. Temporal ocular coherence tomography-measured changes in anterior chamber angle and diurnal intraocular pressure after laser iridoplasty: IMPACT study. Br J Ophthalmol. 2017 Jul;101(7):886-891.
3. Desmond T, Tran V, Maharaj M, Carnt N, White A. Diagnostic accuracy of AS-OCT vs gonioscopy for detecting angle closure: a systematic review and meta-analysis. Graefes Arch Clin Exp Ophthalmol. 2022 Jan;260(1):1-23.
4. Sakata LM, Lavanya R, Friedman DS, Aung HT, Seah SK, Foster PJ, Aung T. Assessment of the scleral spur in anterior segment optical coherence tomography images. Arch Ophthalmol. 2008 Feb;126(2):181-5.
5. Sakata LM, Lavanya R, Friedman DS, Aung HT, Gao H, Kumar RS, Foster PJ. Comparison of Gonioscopy and Anterior Segment Ocular Coherence Tomography in Detecting Angle Closure in Different Quadrants of the Anterior Chamber Angle. Ophthalmology 2008;115:769–774.

Contributors: *Professor Rupert Bourne FRCOphth MD, Cambridge University Hospital, United Kingdom Mr Toby Al-Mugheiry, FRCOphth, Cambridge University Hospital, United Kingdom

Tip of the Month manager: Frances Meier-Gibbons
Tip of the Month editorial board: Francisco Goni, Karl Mercieca, Humma Shahid
Tip of the Month editors in chief: Manuele Michelessi, Francesco Oddone