Scanning Laser Polarimetry with Variable Corneal Compensation in Primary Angle-closure Glaucoma

Purpose: To evaluate the diagnostic sensitivity of scanning laser polarimetry in primary angle-closure glaucoma (PACG) as compared with that in primary open-angle glaucoma (POAG) and to compare the retinal nerve fiber layer (RNFL) distribution between PACG and POAG. Design: Prospective, comparative, observational cases series. Participants: One eye each of 58 PACG patients and 51 POAG patients. Methods: Scanning laser polarimetry with variable corneal compensation (GDx VCC). Main Outcome Measures: GDx VCC temporal-superior-nasal-inferior-temporal (TSNIT) parameters, including TSNIT average, TSNIT standard deviation, superior average, and inferior average, as well as the nerve fiber indicator (NFI). Results: By using a logistic marginal regression model that defined an abnormal test as P<5% for each of the TSNIT parameters or NFI ≥ 31, we found that diagnostic sensitivities of the GDx VCC parameters were similar (all Ps>0.05) in PACG and POAG despite the differences in refraction error (P = 0.017), axial length (P<0.001), and disc diameters (vertical, P = 0.031; horizontal, P = 0.002) between these 2 forms of glaucoma. The between-group similarity in the diagnostic sensitivity remained true either when all eyes were considered together or in each severity group, based on the visual field scoring system adopted by the Advanced Glaucoma Intervention Study. Regarding the RNFL distribution, the parameter inferior average was greater than the superior average in either PACG (P = 0.010) or POAG (P = 0.006). Further subgroup analyses found significant superior-inferior asymmetry in mild PACG (P = 0.022) but not in mild POAG (P = 0.279). Conclusions: Eyes with PACG have ocular biometrics and, possibly, pathogeneses of optic nerve damage different from those of eyes with POAG; however, the diagnostic sensitivity of GDx VCC is quite comparable in these 2 forms of glaucoma, irrespective of disease severity.