The diagnostic properties of a nerve-fiber analyzer in glaucoma

Abstract

Objective: To determine the diagnostic properties of the GDx 400 (Laser Diagnostic Technologies, San Diego, CA, USA) nerve-fiber analyzer in normal and in glaucoma patients compared with a battery of glaucoma tests used by glaucoma experts as gold standard.

Methods: Patients with and without glaucoma underwent a complete eye evaluation, automated perimetry, scanning laser polarimetry with the GDx 400, and opticdisc photography. Two glaucoma experts graded each study eye. Two-by-two tables were constructed for 5 GDx parameters (average thickness, superior average, inferior average, ellipse average, and ellipse modulation) and the GDx number. Receiver operating characteristic (ROC) curves were generated.

Results: The study included 355 patients (171 normal, 184 glaucoma). The mean values of the 5 GDx parameters were lower for the glaucoma than for the normal group. The sensitivity and specificity of the GDx 400 were 45.4% and 91.9% if the cutoff level of the GDx number was 71. Ellipse modulation (EM) measures have the best ROC curve with area under the curve of 0.725.

Conclusion: The GDx 400 nerve-fiber analyzer is primarily used as a screening tool to detect the presence or absence of glaucoma. Its accuracy can be improved with use of continuous corneal compensator.