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D. S. Grewal, M. Sehi, D. S. Greenfield, Advanced Imaging in Glaucoma Study Group; The Impact of Retardance Pattern Stability on Retinal Nerve Fiber Layer Thickness Measurements Over Time Using Scanning Laser Polarimetry With Variable and Enhanced Corneal Compensation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2976.
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© ARVO (1962-2015); The Authors (2016-present)
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).
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.
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).
GDxECC reduces the incidence of TSS variability in stable and progressing eyes, and reduces the bias contributed to longitudinal RNFL thickness assessment.
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