Lens/pupil size and angles are potential anterior segment parameters clinicians can use to differentiate pupillary block from plateau iris configuration, a study in the Journal of Glaucoma suggests.

Researchers from Texas did a retrospective review of swept-source anterior segment OCT (AS-OCT) images of 100 narrow angle eyes. Plateau iris configuration was identified by ultrasound biomicroscopy and/or clinically through iridoplasty. Masked graders analyzed images through anterior chamber analysis and interpretation software to identify scleral spur landmarks and calculate anterior chamber, peripheral angle, iris size and shape and lens/pupil size parameters.

The investigation included 66 pupillary block and 34 plateau iris configuration eyes of 100 participants. The study found several significant differences between the two conditions, including AS-OCT 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 parameters, and all except superior central iris vault parameters.

On threshold evaluation, lens/pupil parameters were the most significant factors, followed by margin-center point-scleral spur landmark angles.

The authors noted that pupil size parameters and pupillary margin-center point-scleral spur landmark angle are the most reliable novel AS-OCT parameters to distinguish between the two conditions, and these parameters do not rely on the visibility of the posterior iris surface, which is difficult to identify with AS-OCT. However, the parameters may be dependent on ambient lighting.

Further study is needed to determine a landmark peripheral to the centroid of the iris, the investigators suggest.

Crowell EL, Chuang AZ, Bell N, et al. Using anterior segment optical coherence tomography (ASOCT) parameters to determine pupillary block versus plateau iris configuration. Journal of Glaucoma. September 24, 2020. [Epub ahead of print].