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B. Nguyen, G. Vizzeri, P. A. Sample, R. N. Weinreb, P. Sassani, F. A. Medeiros, C. A. Girkin, J. M. Liebmann, L. M. Zangwill; Effect of Age and Race on Retinal Nerve Fiber Layer (RNFL) Thickness and Birefringence in Healthy Eyes in the African Descent and Glaucoma Evaluation Study (ADAGES). Invest. Ophthalmol. Vis. Sci. 2010;51(13):2729.
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To evaluate the effect of age and race on retinal nerve fiber layer (RNFL) thickness and birefringence in healthy eyes.
603 healthy eyes of 577 subjects (mean age: 46.8±14.8 years, range: 18-90), 303 of European descent (ED) and 300 of African descent (AD) enrolled in the Diagnostic Innovations in Glaucoma Study (DIGS) and the African Descent and Glaucoma Evaluation Study (ADAGES). Scanning laser polarimetry (SLP, GDx VCC) and time domain optical coherence tomography (OCT) RNFL thickness measurements taken at baseline were used to calculate average and sectoral RNFL birefringence based on the following equation:RNFL Birefringence=RNFL retardance (nm): (SLP RNFL thickness*0.67)/RNFL thickness (um).
In these healthy eyes, although differences were small (< 3 um), OCT average RNFL thickness was significantly (p<.001) greater in AD than ED eyes, while GDx TSNIT average was lower in AD than ED eyes. Average birefringence was significantly lower in AD eyes than in ED eyes (0.34±0.03 versus 0.37±0.05 nm/um, respectively, p<0.001). In both AD and ED eyes, OCT mean RNFL thickness decreased with age at a faster rate (2 um per decade p<0.001, R2=7% and 8%, respectively) than the GDx TSNIT average (.06 um per decade in AD) . Birefringence was significantly, although weakly, associated with age in ED eyes overall and in all 4 quadrants, (R2=0.06; p<0.001 for the average birefringence with a 0.007 nm/um increase in birefringence per decade). In AD eyes, birefringence increased with age overall, and in the nasal and temporal quadrants but not in the superior and inferior quadrants.
RNFL thickness differed by race and decreased with age but the strength of the association depended on the instrument used to measure it. The differences in measured RNFL thickness by SLP and OCT may be related to differences in measured birefringence by race.
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