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Editors Selection IGR 19-4

Examination methods: Laser scanning: Angle morphology and OCT

Comment by Tin Aung on:

18053 Anterior segment optical coherence tomography for imaging the anterior chamber after laser peripheral iridotomy, Memarzadeh F; Li Y; Chopra V et al., American Journal of Ophthalmology, 2007; 143: 877-879

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Laser peripheral iridotomy (LPI) is the recommended first-line intervention in eyes with angle closure, where the primary underlying mechanism is pupil block. A previous study has documented changes in angle morphology after LPI using ultrasound biomicroscopy (UBM) and gonioscopy.¹ However, gonioscopy is difficult to perform in a reproducible fashion, limiting the ability to quantify changes in the angle after LPI. UBM requires a water bath on the eye, is relatively cumbersome to perform and the patient has to be in a supine position.

In this study by Memarzadeh et al. (559),the new anterior segment OCT (AS-OCT) system was used to evaluate change.s in the angle after LPI.

AS-OCT was able to identify subtle but clinically important changes in angle morphology and was capable of quantifying this

AS-OCT uses a longer 1.3mm wavelength light source, allowing deeper penetration and cross-sectional imaging of the anterior chamber and angle, with the benefits of being a rapid, non-contact method that may be performed by a technician.The study found increases in the angle opening distance, angle recess area and trabecular-iris space area post-LPI, with a corresponding increase in mean gonioscopy grade.AS-OCT was therefore able to identify subtle but clinically important changes in angle morphology and was capable of quantifying this. This makes the device a useful tool in assessing angle changes over time. Image processing with the described angle analysis software requires the operator to accurately define the position of the scleral spur on the image before the angle variables can be calculated. This step introduces some variability. In some eyes, the scleral spur can be difficult to identify with AS-OCT. Only the nasal and temporal quadrants were analyzed in the study. Imaging of the superior and inferior quadrants may be difficult to perform with AS-OCT due to the eyelids.

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