GDx staging system: a new method for retinal nerve fiber layer damage classification.

PURPOSE: To provide a reliable and easy-to-use method for classifying retinal nerve fiber layer (RNFL) damage using the parameters obtained by the scanning laser polarimeter with variable corneal compensator (GDx VCC).

METHODS

GDx Staging System is a new method that uses the superior and inferior RNFL thickness values plotted on an x-y diagram to classify GDx VCC results. RNFL defects are classified into 6 stages of increasing severity and 3 classes of defect localization (superior, inferior, or diffuse defect). The diagram was created based on 320 GDx VCC tests from 84 healthy controls and from 236 patients affected by ocular hypertension or chronic open-angle glaucoma. Sensitivity and specificity of the method were assessed in a different cohort that included 161 patients with either ocular hypertension or open-angle glaucoma, and 34 normal participants. The results were correlated with both a clinical classification of the GDx VCC results and with visual field defects classified with the Glaucoma Staging System 2.

RESULTS

Sensitivity and specificity of the GDx Staging System were, respectively, 88.2% and 100%. Correlations with the clinical classification and the Glaucoma Staging System 2 results were statistically significant (Spearman correlation coefficient 0.92 and 0.57, respectively; P<0.0001).

CONCLUSIONS

The GDx Staging System is an easy and quick method for interpreting GDx VCC results. It can be clinically useful, especially for nonexpert ophthalmologists.