When using anterior segment optical coherence tomography (AS-OCT) to determine the difference between eyes with pupillary block (PB) or plateau iris configuration (PIC), researchers found that pupil size parameters and pupillary margin-center point-scleral spur landmark (PM-C-SSL) angle are potentially the most reliable parameters.

Their study, published in the Journal of Glaucoma, was conducted to distinguish mechanisms of angle closure with retrospective swept-source Fourier domain AS-OCT images from narrow angle eyes. The study defined PIC with ultrasound biomicroscopy and/or an iridoplasty. A masked reader read the images with Anterior Chamber Analysis and Interpretation software, identifying scleral spur landmarks and calculating anterior chamber, peripheral angle, iris size, iris shape, and lens/pupil size parameters. Researchers summarized and compared AS-OCT parameters with a 2-sample t test. They calculated thresholds and area under receiver operating characteristic curve using logistic regression analysis.

Investigators reviewed 100 hundred eyes (66 PB and 34 PIC) and found that, of all AS-OCT parameters, the following were significantly different between PB and PIC: 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. 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), on threshold evaluation.


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“We propose that the pupil size parameters and PM-C-SSL angle are the most reliable novel AS-OCT 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 AS-OCT, but may be ambient lighting dependent,” researchers report.

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

The study’s limitations were that it was retrospective, it had a small sample size, axial length measurements were excluded, and it didn’t address issues with visualizing the posterior layer of pigment epithelium with AS-OCT at the peripheral iris. “The inability to visualize the posterior layer of pigment epithelium affects all AS-OCT machines, which is why we propose using the pupil size parameters and PM-SSL-C angle as the most reliable measurements to distinguish between the 2 conditions,” researchers write.

Reference

Crowell EL, Chuang AZ, Bell NP, Blieden LS, Feldman RM. Using anterior segment optical coherence tomography (asoct) parameters to determine pupillary block versus plateau iris configuration. J Glaucoma. 2020;29(11):1036-1042. doi: 10.1097/IJG.0000000000001664