Diagnostic accuracy of the GDx VCC for glaucoma

Purpose: To determine the diagnostic accuracy of the GDx VCC in the diagnosis of glaucoma. Design: Prospective, comparative, observational, clinic-based case series. Participants: One eye each of 77 healthy subjects and 162 patients with primary open-angle glaucoma of Caucasian racial origin. Healthy subjects had normal visual fields (VFs), healthy-looking optic discs, and intraocular pressures of less than or equal to21 mmHg in both eyes. Glaucoma patients had a reproducible glaucomatous VF defect and a glaucomatous appearance of the optic disc in at least one eye. Methods: All subjects were measured with the GDx VCC with an automated variable corneal compensator. We constructed receiver operating characteristic (ROC) curves for all available parameters. Subsequently, we calculated sensitivity, specificity, and multilevel likelihood,ratios for the best discriminating parameter in the entire group. In addition, we calculated sensitivity and specificity in patients with mild, moderate, and severe glaucomatous damage separately. Main Outcome Measures: Software-derived parameters TSNIT (temporal, superior, nasal, inferior, temporal) Average, Superior Average, Inferior Average, TSNIT Std. Dev. (standard deviation), and Nerve Fiber Indicator (NFI). Results: The areas under the ROC curve for TSNIT Average, Superior Average, Inferior Average, TSNIT Std. Dev., and NFI were 0.93, 0.94, 0.90, 0.92, and 0.98, respectively. For the best discriminating parameter NFI, the sensitivity and specificity with a cutoff point of greater than or equal to40 were 89.0% and 95.9%, respectively. The multilevel likelihood ratios for glaucoma were 0.07 at NFI values of <35, 1.30 at values between 35 and 44, and 61.50 at values of greater than or equal to44. At the cutoff level of greater than or equal to40, the sensitivities of the NFI for correctly identifying glaucoma patients with mild, moderate, and severe damage were 83.8%, 92.9%, and 90.1%, respectively. Conclusions: The GDx VCC allowed easy, rapid, and accurate discrimination between healthy and glaucomatous eyes. The NFI was the best discriminating parameter. The GDx VCC seems to fulfill criteria for a glaucoma screening device. (C) 2004 by the American Academy of Ophthalmology.