PRéCIS:: The potential parameters for differentiating pupillary block (PB) from plateau iris configuration (PIC) on anterior segment optical coherence tomography (ASOCT) are lens/pupil size parameters and angles. Further study is needed to determine a landmark peripheral to the centroid of the iris.
Purpose: Investigate anterior segment parameters to distinguish between 2 mechanisms of angle closure, PB and PIC, using swept-source Fourier domain ASOCT.
Patients and methods: Retrospective ASOCT images from narrow angle eyes were reviewed. PIC was defined either by ultrasound biomicroscopy and/or clinically when an iridoplasty was performed. Images were read by a masked reader using Anterior Chamber Analysis and Interpretation software to identify scleral spur landmarks and calculate anterior chamber, peripheral angle, iris size, iris shape, and lens/pupil size parameters. ASOCT parameters were summarized and compared using the 2-sample t test. Thresholds and area under receiver operating characteristic curve were calculated using logistic regression analysis.
Results: One hundred eyes (66 PB and 34 PIC) of 100 participants were reviewed. Of all ASOCT parameters, iris length in each quadrant, pupil arc, lens/pupil parameters (pupil arc, lens vault, and pupil diameter), all pupillary margin-center point-scleral spur landmark (PM-C-SSL) parameters, and all except superior central iris vault parameters were significantly different between PB and PIC. On threshold evaluation, lens/pupil parameters had the greatest area under receiver operating characteristic curve values (0.77 to 0.80), followed by PM-C-SSL angles (0.71 to 0.75).
Conclusions: We propose that the pupil size parameters and PM-C-SSL angle are the most reliable novel ASOCT parameters to distinguish between PB and PIC eyes. These parameters do not rely on the visibility of the posterior iris surface, which is difficult to identify with ASOCT, but may be ambient lighting dependent.