The diagnostic properties of a nerve-fiber analyzer in glaucoma: Potential use as a screening or diagnostic tool
Patricia M. Khu, MD, MS, Edgardo U. Dorotheo, MD, Lawrence Tinio, MD, Cynthia P. Cordero, MS, Manuel B. Agulto, MD
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.
Keywords: Glaucoma, Retinal nerve-fiber layer, Nerve-fiber analyzer, Scanning laser polarimetry