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Chandrasekhar Garudadri, Harsha L. Rao, Ravi K. Yadav, Uday K. Addenapalli; Predictors And Repeatability Of Normal Retinal Nerve Fiber Layer Measurements By Gdx Enhanced Corneal Compensation. Invest. Ophthalmol. Vis. Sci. 2012;53(14):728.
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To evaluate the (i) effects of age, axial length, typical scan score (TSS) and corneal birefringence on the normal retinal nerve fiber layer (RNFL) measurements and (ii) repeatability of RNFL measurements with GDx enhanced corneal compensation (ECC).
In an observational, cross-sectional study, 140 eyes of 73 normal subjects of Indian origin underwent RNFL imaging with GDx ECC. Linear mixed modeling methods were used to evaluate the effects of age, axial length, TSS and corneal birefringence on the RNFL measurements. One random eye of 48 subjects from the cohort underwent 3 serial scans during the same session to determine the repeatability of measurements.
Age significantly influenced the RNFL measurements. Nerve fiber indicator (NFI) increased by 1.3 units while RNFL thickness decreased by 1 µm for every decade increase in age. TSS affected the overall average RNFL thickness (TSNIT average) measurement significantly; a 10 units decrease in TSS increasing the TSNIT average thickness measurement by 6 µm. TSS did not influence the other RNFL measurements. Axial length as well as the corneal birefringence measurements did not influence any of the RNFL measurements of GDx ECC. Repeatability of RNFL thickness measurements, as assessed by coefficient of variation (CVw) ranged between 1.7% for TSNIT average and 3.1% for TSNIT standard deviation while the same for NFI was 11.4%.
Age had a significant effect on all RNFL measurements of GDx ECC while TSS had a significant effect on the overall average thickness measurement. Axial length as well as the corneal birefringence measurements did not influence any of the measurements. RNFL thickness measurements of GDx ECC also had excellent intrasession repeatability. These results are important while evaluating change in the structural measurements over time in glaucoma patients.
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