Using Anterior Segment Optical Coherence Tomography (ASOCT) Parameters to Determine Pupillary Block versus Plateau Iris Configurations

Abstract

Purpose : To investigate which anterior segment parameters can be used to distinguish between 2 mechanisms of angle closure: pupillary block (PB) and plateau iris (PI) configurations, using Swept Source Fourier Domain ASOCT

Methods : ASOCT images from prior IRB-approved studies with narrow angle eyes were reviewed. PI configuration was defined either by ultrasound biomicroscopy and/or clinically when an iridoplasty was performed. All ASOCT imaging was performed in the dark with the CASIA SS-1000 (Tomey, Nagoya, Japan) instrument using the angle analysis 3D mode. Images were read by an experienced, masked reader using customized software to identify the scleral spur landmarks (SSL). The software then interpreted and calculated the following (Figure 1): scleral spur landmark line (SSLL); anterior chamber width (ACW), depth (ACD), area (ACA), and volume (ACV); lens vault (LV); pupil arc (PA) and pupil arc area (PAA); center point of SSLL-pupil margin angle (CPMA); iris area (IA) and volume (IV); central iris-scleral spur angle (CISSA); pupil margin-scleral spur angle (PMSSA); angle between central iris-scleral spur and pupil margin-scleral spur (CIPMA); central iris vault (CIV, length between central iris to SSLL); and pupil margin vault (PMV, length between pupil margin and SSLL). ASOCT parameters were summarized and compared using a 2-sample t-test.

Results : 78 eyes (67 PB and 11 PI) of 78 participants were reviewed. There were no differences between groups demographically. Of all studied ASOCT parameters, mean PA (both horizontal and vertical) was 0.72 mm (18%) larger (P=0.016) and mean PAA was 4.27 mm² (32%) larger (P=0.026) in PI eyes than PB eyes. Mean CPMA was 8 degrees (35% at temporal, superior, inferior) to 9 degrees (41% at nasal) smaller (P<0.001), mean CIV was 0.13 mm (22% at nasal, superior and temporal) to 0.16 mm (26% at inferior) smaller (P<0.017), and PMV was 0.18 mm (22% at inferior) to 0.22 mm (31% at nasal) smaller (P<0.005) in PI eyes (Figure 2).

Conclusions : The parameters that can potentially be used to differentiate PI from PB are larger PA or PAA and a smaller CPMA, PMV or CIV.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Illustration of 2D ASOCT parameters. C=midpoint of SSLL; CI=iris centroid; PM=pupil margin.

 

Illustration of significant 2D ASOCT parameters from this study.