Swept-source OCT for measuring peripheral anterior synechiae
Reviewed by Brian Ang

The authors report on a cross-sectional study looking at swept-source optical coherence tomography (SS-OCT) for measuring the area and degree of peripheral anterior synechiae (PAS) in patients with angle closure glaucoma. The SS-OCT is commercially available, has a laser wavelength of 1,310nm, scan speed of 30,000 A-scans per second, and axial resolution of less than 10 microns. In this study, selection of the ‘angle analysis’ protocol with 128 radial B-scans, allowed 360-imaging of the entire angle in 2.4 seconds. For each radial scan, the scleral spur and anterior irido-angle adhesion (iris end point) was manually detected; following which the built-in software would measure the extent of PAS in each meridian. These could then be reconstructed in 3D. Scans were performed for 23 eyes of 20 patients with chronic angle closure glaucoma with PAS as confirmed on indentation gonioscopy. The mean area of PAS was 20.8(±16.9)mm2, while the mean degree of PAS involvement was 186.5(±79.9) degrees. There was good agreement between SS-OCT and gonioscopy photographs, with a kappa value of 0.79. Interobserver variability was low with a high interobserver intraclass correlation coefficient of 0.99. Additionally, it was possible to distinguish between appositional and synechial angle closure – the angle would open in the light in appositional angle closure but would remain closed in synechial angle closure. SS-OCT is an exciting imaging tool for assessing the drainage angle because it is able to provide non-contact, fast, reproducible and objective measurements of PAS. This allows PAS progression and extent to be assessed more meaningfully, especially in the context of intraocular pressure control and glaucoma progression. 

Anterior chamber angle imaging with swept-source optical coherence tomography: measuring peripheral anterior synechiae in glaucoma.
Lai I, Mak H, Lai G, et al.
OPHTHALMOLOGY
2013;120:1144-9.