Diagnostic Abilities of Variable and Enhanced Corneal Compensation Algorithms of GDx in Different Severities of Glaucoma

Purpose: To compare the abilities of retinal nerve fiber layer (RNFL) parameters of variable corneal compensation (VCC) and enhanced corneal compensation (ECC) algorithms of scanning laser polarimetry (GDx) in detecting various severities of glaucoma. Methods: Two hundred and eighty-five eyes of 194 subjects from the Longitudinal Glaucoma Evaluation Study who underwent GDx VCC and ECC imaging were evaluated. Abilities of RNFL parameters of GDx VCC and ECC to diagnose glaucoma were compared using area under receiver operating characteristic curves (AUC), sensitivities at fixed specificities, and likelihood ratios. Results: After excluding 5 eyes that failed to satisfy manufacturer-recommended quality parameters with ECC and 68 with VCC, 56 eyes of 41 normal subjects and 161 eyes of 121 glaucoma patients [36 eyes with preperimetric glaucoma, 52 eyes with early (MD > -6 dB), 34 with moderate (MD between -6 and -12 dB), and 39 with severe glaucoma (MD < -12 dB)] were included for the analysis. Inferior RNFL, average RNFL, and nerve fiber indicator parameters showed the best AUCs and sensitivities both with GDx VCC and ECC in diagnosing all severities of glaucoma. AUCs and sensitivities of all RNFL parameters were comparable between the VCC and ECC algorithms (P > 0.20 for all comparisons). Likelihood ratios associated with the diagnostic categorization of RNFL parameters were comparable between the VCC and ECC algorithms. Conclusion: In scans satisfying the manufacturer-recommended quality parameters, which were significantly greater with ECC than VCC algorithm, diagnostic abilities of GDx ECC and VCC in glaucoma were similar.