Retinal Nerve Fiber Layer Thickness Measurement by Scanning Laser Polarimetry (GDxVCC) at Conventional and Modified Diameter Scans in Normals, Glaucoma Suspects, and Early Glaucoma Patients

PURPOSE: To study the retinal nerve fiber layer (RNFL) at 3 different scan diameters using GDxVCC in healthy, primary open-angle glaucoma (POAG) suspects, and early POAG. METHOD: RNFL parameters were evaluated in 100 normal subjects, 50 POAG suspects, and 50 early POAG patients using GDxVCC at conventional small, medium, and large circle. TSNIT (temporal, superior, nasal, inferior, temporal) average, superior average, inferior average RNFL thickness, and nerve fiber indicator (NFI) were evaluated. RESULTS: The TSNIT average (microm) in normal subjects, POAG suspects, and POAG at 3 different circles was 54.17+/-4.6, 49.96+/-6.5, 46.92+/-6.2 (small); 47.17+/-4.8, 43.79+/-5.7, 41.48+/-6.5 (medium); and 41.57+/-4.6, 39.77+/-5.9, 38.33+/-7.1 (large). All RNFL parameters at all circles showed significant difference between normal and early POAG eyes (P<0.001). Area under the curve was 0.911 for NFI at all circles. All parameters at small and medium circle, all except TSNIT average at large circle showed significant difference between normal and POAG suspects (P<0.001), area under curve being the highest (0.780 to 0.801 at 3 circles) for NFI. All parameters progressively decreased with increasing diameter with significant difference between small-medium (P<0.001), medium-large (P<0.001), and small-large circle results (P<0.001) in all the groups for all parameters except NFI. CONCLUSIONS: Medium and large circles can also be used for RNFL evaluation in glaucoma. NFI is the best discriminating measure across all scan diameters.