A total of 78 subjects, with both narrow and open ACAs (34 male and 44 female), attended one of two screening days. Demographic and summary data for open and narrow angle groups are summarized in
Table 1, with a subject being classified as having gonioscopically narrow angles if either eye satisfied the criteria. Subjects were aged between 30 and 83 years with median age of 66 years (interquartile range [IQR] 53 to 79). Self-reported ethnicities were 56% white and 35% South Asian. Subjects classified with narrow angles were statistically significantly older (
P = 0.008, ISGEO classification;
P = 0.046, classification based on clinical opinion of occludability), and had higher IOPs (
P = 0.038, ISGEO classification;
P = 0.009, classification based on clinical opinion) than those in the open angle group. By defining a narrow angle as ≥270° nonvisibility of the posterior trabecular meshwork (ISGEO classification), 46% (
n = 36) and 54% (
n = 42) of subjects were diagnosed with open and narrow ACAs, respectively. The percentage with narrow angles fell to 21.8% (
n = 17) if the clinical opinion of occludability was used as the cutoff criterion.
In our cohort, the biomicroscope-based tests (van Herick and Smith's) and reference comparison gonioscopic examination captured data of suitable quality for analysis in 100% of eyes (n = 145). Following repeat acquisition in accordance with the study protocol, the imaging-based systems (Visante OCT and Pentacam) acquired adequate-quality data for the measurement of ACA and ACD in 88% to 97%, and 96% to 100% of eyes, respectively, with Pentacam nasal ACA being the parameter with the greatest proportion of data excluded from analysis (12% for left eye data). No bias was observed between narrow and open angle groups for data excluded on the basis of poor quality.
For the primary analysis, the diagnostic performance of each index test was evaluated against two gonioscopy reference standards (ISGEO classification and clinician's judgment of occludability) and using the eye as the unit of analysis. The analysis was repeated using the individual as the unit of analysis, yielding similar results (data not shown).