Preperimetric glaucoma assessment with scanning laser polarimetry (GDx VCC): analysis of retinal nerve fiber layer by sectors

PURPOSE: To evaluate the capability of the GDx VCC nerve fiber analyzer to detect preperimetric glaucoma across 12 retinal nerve fiber layer (RNFL) peripapillary sectors. METHODS: Data were obtained in a cross-sectional, hospital clinic-based study; 699 eyes from 699 glaucoma suspects were enrolled in this protocol. All subjects underwent ophthalmologic examination, static automated perimetry [Humphrey 24-2 Swedish interactive threshold algorithm (SITA) Standard], optic nerve stereoscopic photographs, red-free digital RNFL photographs and GDx VCC examination. Group S included 283 normal eyes and 39 preperimetric glaucoma eyes with RNFL superior or diffuse defects in the fiber layer photographs. Group I included 324 normal subjects and 24 with preperimetric glaucoma eyes with RNFL inferior or diffuse defects in fiber layer photographs. RESULTS: Mean values of the area under the curve (AUC) for receiver operating characteristic analysis for inferior average (Inf Avg), temporal-superior-nasal-inferior temporal average (TSNIT Avg), superior average (Sup Avg), and the nerve fiber indicator were significantly less in the eyes with RNFL defects than the control group compared with the AUC for thickness at hour 12 and at hour 6 calculated from the RNFL sector density. The AUC for receiver operating characteristic analysis of the new parameters improved by 12% with respect to the best GDx VCC standard values. CONCLUSIONS: Our results confirm that the 12 sector divisions of the GDx VCC have better diagnostic reliability in preperimetric glaucoma, and are able to improve the discrimination capability between normal and early damaged RNFLs.