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Danny Y. Leung, Michael Sinai, Ben Jang; Effect Of Magnification Correction On RNFL Measurements With RTVue FD-OCT System. Invest. Ophthalmol. Vis. Sci. 2011;52(14):183.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the effect of magnification correction on RNFL measurements with RTVue FD-OCT system (Optovue, Fremont, CA).
859 healthy eyes from the Optovue Normative Database were included in this study. Peripapillary RNFL thickness was measured using the ONH scan pattern which provides RNFL thickness from a circle 3.45 mm in diameter centered on the optic disc. The RTVue FD-OCT automatically optimizes focus, polarization, and depth positioning (z-motor) for each scan. The effect of magnification errors on RNFL thickness was determined by comparing thickness values with and without thickness values corrected based on axial length as well as refractive error. Mean differences were compared as well as correlation with axial length to differentiate the effect of axial length per se on RNFL thickness vs the effect of axial length and magnification errors (as with the uncorrected measurements).
Mean refractive error was -0.51±1.94 diopters with a range from -7.75 to 5.50. Mean axial length was 23.70±1.1 µm. Uncorrected mean RNFL thickness was 102.32±9.16 µm, and correlation with axial length was r = 0.190, (R2 = 0.0362, n.s.). Mean RNFL thickness after correction for magnification errors based on axial length was 102.19±9.10 µm, and correlation with axial length was r = 0.141, n.s. (R2 = 0.020). Mean RNFL thickness after correction for magnification errors based on refractive error was 102.35±9.12 µm, and correlation with axial length was r = 0.17, n.s. (R2 = 0.0289).
Differences in RNFL thickness with and without magnification correction was small as expected in this group of healthy eyes with small refractive errors (on average). We found a significant correlation between axial length and RNFL thickness (uncorrected). When magnification errors were corrected for either using axial length or refraction, the correlation between axial length and RNFL thickness became smaller, and was no longer significant. Correcting for magnification errors may improve the accuracy of the RNFL thickness values.
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