Abstract
Purpose: :
To examine the impact of retardance pattern stability on retinal nerve fiber layer thickness (RNFLT) measurements over time using scanning laser polarimetry with variable (GDxVCC) and enhanced corneal compensation (GDxECC).
Methods: :
Glaucoma suspect and glaucomatous eyes with ≥3 years of follow-up were prospectively enrolled. All eyes underwent standard automated perimetry (SAP), GDxVCC and GDxECC (Carl Zeiss Meditec, Dublin, CA) every six months. The typical scan score (TSS) was extracted as a measure of retardance pattern quality. Atypical retardation pattern (ARP) was defined as TSS<80. Progression was determined using pointwise linear regression analysis of SAP sensitivity values using ProgressorTM (Medisoft, Inc., London, UK) and defined as a loss of -1dB/year at p<0.01 on 2 consecutive examinations. Within-subject variance (SD2) of TSS and RNFL measurements was calculated for each patient.
Results: :
One hundred and six eyes were enrolled (59 glaucoma suspect, 47 glaucoma) with a mean follow-up of 45.1±5.4 months. Twenty-one eyes (19.8%) demonstrated SAP progression over time. Baseline TSS was similar among stable and progressing eyes using GDxVCC (85.5 ± 20.8 vs 86 ± 17.7, p = 0.9) and GDxECC (98.7 ± 4.3 vs 99.7 ± 1.5, p = 0.1). At baseline, 25 eyes (23.5%) had ARP using VCC vs 1 eye (0.9%) using ECC. The within-subject variance of TSS was significantly lower using GDxECC compared with GDxVCC in stable (9.1±22.2 vs 77.7±143.9, p<0.001) and progressing eyes (6.4±14.1 vs 58.8±86.7, p=0.01). The variance of average, superior and inferior RNFLT was significantly (p<0.001, p=0.03, p=0.01) correlated with TSS variance using GDxVCC (r=0.48, r=0.22, r=0.25) but not (p>0.05) with GDxECC (r=0.12, r=0.11, r=0.13). Each 1-unit of increase in TSS was associated with a 0.14 µm decrease in RNFLT using SLPVCC (r= -0.33, p<0.001).
Conclusions: :
GDxECC reduces the incidence of TSS variability in stable and progressing eyes, and reduces the bias contributed to longitudinal RNFL thickness assessment.
Keywords: imaging/image analysis: clinical