Reliability analyses of the GDx nerve-fiber analyzer
Patricia M. Khu, MD, MS, Edgardo U. Dorotheo, MD, Lawrence Tinio, MD, Cynthia P. Cordero, MS, Manuel B. Agulto, MD
The scanning laser polarimetry, exemplified by the GDx 400 (Laser Diagnostic Technologies, San Diego, CA, USA) nerve-fiber analyzer, allows noninvasive quantitative assessment of the retinal nerve-fiber layer. This study determined the reliability of the GDx 400 in taking repeat measurements by different operators and at different sessions in a sample of normal and glaucoma patients.
Patients with and without glaucoma underwent a complete eye evaluation, automated achromatic perimetry, scanning laser polarimetry, and optic-disc photography. Retinal nerve-fiber layer (RNFL) measurements were obtained for each group of patients by two trained operators who were masked as to the status of the study eye. Four measurements were obtained for each study eye in the same session and in another session. Reliability measures using intraclass correlation coefficient of five preselected GDx parameters were obtained.
The study recruited 355 patients (171 normal, 184 glaucomatous) ages 30 to 78 years. Intraclass correlation coefficients within operator same session (0.84-0.95), within operator different sessions (0.78-0.93), between operators same session (0.79-0.94), and between operators different sessions (0.80-0.94) were excellent. The reliability measures for the second session (0.79-0.94) were higher than for the first session (0.79-0.87) even for measurements taken by the same operator.
The GDx 400 nerve-fiber analyzer has good reliability measures and can be used to monitor changes in the RNFL thickness over time. Change in measurements exceeding 20% from baseline should be considered as possible progression.
Keywords: Glaucoma, Retinal nerve-fiber layer, Nerve-fiber analyzer, Scanning laser polarimetry