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A. M. Hwang, D. J. Salchow; Refractive Error and Optical Coherence Tomography (OCT) of the Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1081.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of refractive error on optical coherence tomography (OCT) measurements of retinal nerve fiber layer (RNFL) thickness, macular thickness and optic disc parameters.
Fifteen eyes of fifteen healthy subjects (5 females; 8 Asians, 6 Caucasians,1 Hispanic) were dilated with phenylephrine 2.5% eye drops. Optic disc parameters, RNFL, and macular thickness were measured with StratusOCT (software version 4.0.1; Carl Zeiss Meditec Inc., Dublin, CA) using fast scan modes without contact lens (CL), and with soft CL (Proclear Sphere, base curvature 8.6 mm, diameter 14.2 mm, CooperVision Inc., Fairport, NY) of different powers (-10 D, -4 D, +4 D, +10 D), and again without CL. Scans with signal strength of 6 or greater were included. Statistical analysis was performed with Excel 2007 (Microsoft, Redmond, WA).
Mean age (± standard deviation [SD]) was 30.5 ± 3.2 years. Mean global RNFL thickness without CL was 107.0 ± 9.3 µm; with +10 D CL, 105.4 ± 7.5 µm; with -10 D CL, 109.7 ± 9.7 µm (differences statistically significant between -10 D and +10 D, and no CL and -10 D). RNFL thickness without CL and with -10 D CL at 5 and 6 o’clock was significantly different; this was also noted between the +10 D CL and -10 D CL. Statistically significant differences were found in specific segments when comparing the +4 D, +10 D, and -10 D CL to no CL. Mean horizontal cup-to-disc (C:D) ratio without CL was 0.61 ± 0.13, with +10 D CL, 0.62 ± 0.11, with -10 D, 0.61 ± 0.11; mean vertical C:D ratio without CL was 0.55 ± 0.11, with +10 D CL, 0.55 ± 0.10, and with -10 D, 0.54 ± 0.11 (differences not statistically significant). A statistically significant difference was found between the +10 D and -10 D CL in the disc diameter of the individual radial scan analysis. Mean foveal thickness was 209.9 ± 25.5 µm and mean total macular volume was 7.09 ± 0.37 mm3 without CL; with +10 D CL, it was 209.3 ± 22.3 µm and 7.10 ± 0.39 mm3, and with -10D, it was 207.5 ± 25.6 µm and 7.00 ± 0.35 mm3, respectively (not statistically significant). Few macular regions with +4 D, +10 D, and -4 D CL were significantly different from no CL, but only the inferior outer macula was significantly different between -10 D and +10 D CL.
Statistically, but not clinically significant differences in RNFL thickness were found in the mean global thickness and in the inferior quadrant. Few regions of macular thickness were also statistically, but not clinically significant. Foveal thickness, total macular volume, and optic disc ratios were not affected. Differences may be related to signal strength and contact lens centration. We conclude that OCT measurements of the retina and optic disc before and after cataract or refractive surgery, as well as with and without CL may be used with caution for comparison.
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