Longitudinal and Cross-Sectional Analyses of Age and Intraocular Pressure Effects on Retinal Nerve Fiber Layer and Ganglion Cell Complex Thickness

Abstract

Purpose: To study the effect of age and intraocular pressure (IOP) on retinal nerve fiber layer (NFL) and ganglion cell complex (GCC) thickness in normal eyes.

Methods: We analyzed the data from subjects enrolled in the multi-center longitudinal Advanced Imaging for Glaucoma (AIG) Study (www.AIGStudy.net). The data included yearly visits from the normal subjects group in the AIGS study. Fourier-domain optical coherence tomography (OCT) was used to map the thickness of NFL and GCC three times on each visit. To adjust for the repeated measurements for the same subjects, mixed effect models were used to evaluate the longitudinal effect of age and IOP on the NFL and GCC thickness. The measurements at baseline were used to examine the cross sectional effects among individual subjects.

Results: The analysis included 192 eyes of 92 normal participants with follow-up visits between 2009 and 2013. The longitudinal analyses showed the overall GCC thickness on average decreased 0.25 μm per year (p <0.001, standard error = 0.049), while the overall NFL thickness decreased 0.21 μm per year (p<0.001, standard error = 0.04). The cross-sectional analyses showed the GCC thickness was 0.17 μm thinner for each year older (p<0.001, standard error = 0.050), while the RNFL was 0.19 μm thinner for each year older (p=0.003, standard error = 0.065). We did not find significant IOP effect on either GCC or RNFL from either longitudinal or cross-sectional analysis.

Conclusions: NFL and GCC thin with age; they do not seem to be affected by IOP. These results on normal age-related thinning of NFL and GCC can be used to establish criteria to detect abnormally rapid thinning that might indicate glaucomatous progression.