Longitudinal relationship between retinal nerve fiber layer thickness parameters assessed by scanning laser polarimetry (GDxVCC) and visual field in glaucoma

To investigate the longitudinal relationship between retinal nerve fiber layer (RNFL) thickness parameters assessed by scanning laser polarimetry with variable corneal compensation (GDxVCC) and visual field parameters obtained with the Humphrey field analyzer (HFA) in patients with glaucoma, and to assess the usefulness of GDxVCC in longitudinal follow-up. A total of 242 eyes in 122 patients with glaucoma were periodically assessed using GDxVCC and HFA program SITA fast 30-2 for 3-5 years. Eyes with more than four times of reliable HFA and GDxVCC data were obtained from during the follow-up periods were included in the analysis. Changes in HFA parameters (mean deviation [MD], pattern standard deviation [PSD]) and those in GDxVCC parameters (superior average, inferior average, temporal-superior-nasal-inferior-temporal [TSNIT] average, TSNIT standard deviation [SD], nerve fiber indicator [NFI]) were determined by regression analysis. The relationship between HFA and GDxVCC parameters at the initial point and their annual changes were analyzed with canonical correlation analysis and Pearson's correlation coefficients. Twenty-four eyes (9.9%) of 19 patients that met inclusion criteria were statistically analyzed. Longitudinal progression was 0.039 +/- 0.971 dB/year in MD, 0.156 +/- 0.644 dB/year in PSD, -0.197 +/- 0.970 mu m/year in TSNIT average, -0.503 +/- 1.341 mu m/year in superior average, -0.282 +/- 0.974 mu m/year in inferior average, -0.284 +/- 1.013/year in TSNIT SD and 1.269 +/- 2.560/year in NFI. In canonical correlation analysis at the initial point, first canonical variates were not statistically significant between HFA and GDxVCC parameters. First canonical variates of annual changes significantly correlated between HFA and GDxVCC parameters (p < 0.01), with correlation coefficient of 0.85. In Pearson's correlation analysis of each parameter, there was a significant relationship between MD and NFI at the initial point (r = -0.46, p < 0.05). There was a statistically significant relationship between progressions in MD and NFI (r = -0.54, p < 0.01) and in PSD and NFI (r = 0.53, p < 0.01). Longitudinal progression in NFI obtained with GDxVCC was significantly correlated with that in HFA parameters, such as MD and PSD. GDxVCC is a useful tool for longitudinal follow-up assessment of glaucoma.