All baseline values were defined as those under bright lighting conditions. The primary outcome variables were baseline iris area and comparisons between baseline and dark conditions for loss in iris area, percent loss in iris area, loss in iris area per millimeter change in pupil diameter, and percent loss in iris area per millimeter change in pupil diameter. Also estimated were iris volume by a published method and made the same calculations to evaluate loss in iris volume as for iris area. The hypotheses were that these outcomes might be different by origin, type of glaucoma, or by one or more of other variables. Covariates that were considered relevant to evaluate in this study included age, sex, origin, eye (right/left), diagnosis as detailed below, past laser iridotomy, eye color, presenting spherical equivalent refractive error (for phakic eyes), IOP, central corneal thickness, cup-to-disc ratio, blood pressure, Swedish Interactive Thresholding Algorithm Standard 24-2 visual field result (MD, PSD, GHT), ACD, axial length, pupil condition at time of imaging (light, dark, pharmacologically dilated), and pupil diameter. The ASOCT through ASAP provided for each image the nasal and temporal parameters called trabecular iris space area 500 μm and 750 μm from the SS (trabecular iris space area [TISA] 500 and TISA 750, respectively), iris thickness measured 500 μm and 750 μm from SS, angle opening distance at 500 μm or 750 μm (angle opening distance [AOD] 500 and AOD 750, respectively), angle recess area at 500 μm or 750 μm (angle recess area [ARA] 500 and ARA 750, respectively), anterior chamber area (ACA), anterior chamber volume (ACV), and iris concavity ratio. These ASAP parameters were not separately evaluated in images requiring manual ImageJ evaluation due to failed ASAP analysis.
Baseline data were available for 267 eyes. For change from light to dark, data were available for 257 eyes with pupil diameter expansion of 0.5 mm or more; and for change from light to pharmacological pupil dilation, data were available for 130 eyes, all of which had pupil diameter expansion of 0.5 mm or more.
Descriptive statistics (mean and SD) were tabulated for each iris parameter by selected categorical variables of interest, such as origin and diagnosis. Diagnosis was analyzed as six groups or two groups. The six groupings were normal, OAG, OAG suspects (OAGS), primary angle closure (PAC), PAC suspect (PACS), and 6) angle closure glaucoma (ACG). The analysis by two groups consisted of (1) normal, OAG, and OAGS; and (2) PAC, PACS, and ACG. Descriptive statistics were also tabulated for selected variables by origin (number/percent for categorical variables and mean/SD for continuous variables). Origin groups were compared using the χ2 test for categorical variables and analysis of variance or the Kruskall-Wallis test for continuous variables. Univariate linear regression models were used to identify variables associated with each iris parameter. Variables with univariate significance of 0.20 or less were then used to develop a multivariable linear model using the stepwise selection process; the criterion used for a variable to enter a multivariable model and stay in the model was significance of 0.10 or less. Logistic regression models were used to look at the effect of iris parameters on the risk of AC adjusted for origin and the interaction between iris parameters and origin on the risk of AC. For variables with more than two categories and significance of 0.05 or less in a univariate or multivariable model, categories were compared using Tukey-Kramer and Bonferroni adjustments for multiple comparisons in linear and logistic models, respectively. All analyses were performed using SAS 9.2 (SAS Institute, Cary, NC).