A new method for indirect estimation of anterior chamber angle width and for the detection of occludable angles

Abstract

Objective: To describe a new method for indirect estimation of the anterior chamber angle width and to evaluate its efficacy at detecting occludable angles.
Methods: This study included 240 eyes of 240 consecutive patients over 40 years of age with a spherical refraction between -1.50 and +5 diopters. Patients with a history of ocular trauma and/or surgery were excluded. This new method was performed by placing the illumination arm of the slit lamp at an angle of 30° from the microscope. Magnification used was 1.6X. Green light, the illumination setting provided by the red free filter available on the slit lamp, was used. A vertical slit beam of 4 mm of length and a minimum width allowing to perform a biomicroscopic section on the temporal corneal periphery, making the upper and lower edges of the slit coincide with the sclerocorneal limbus, was projected. The method was compared to Van Herick’s one, and then, both were compared, in a masked fashion, with the gold standard method: gonioscopy.
Results: It was established that the angle would be considered occludable if the peripheral anterior chamber depth was not greater than 50% of the adjacent corneal thickness. With this cutoff value the new method had a sensitivity and specificity of 99% (95% CI: 0.945/1.000) and 95.7% (95% CI: 0.855/0.986), respectively. The Area Under the ROC Curve (AUC) was 0.9736 (95% CI: 0.9541/0.9931) vs. 0.6144 (95% CI: 0.5784/0.6504) for the Van Herick’s method.
Conclusions: The results show greater sensitivity and specificity of the new method for the detection of occludable angles vs. the Van Herick’s method.