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S. M. Delgado, A. Martinez, P. Sankaridurg, A. Ho; Comparison of Letter versus Laser Targets on Measuring Central and Peripheral Autorefraction. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3993.
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© ARVO (1962-2015); The Authors (2016-present)
It is known that target types can influence the outcome of refractive measurements due to such effects as accommodative effort, chromatic aberration and depth of focus. We studied the effect of using letter versus laser targets during autorefraction measurement of both central and peripheral refraction.
As part of a larger study to investigate relative peripheral refraction and accommodation, both eyes of five young subjects (age 23 to 28 years, refractive error +0.50D to -0.75D) were measured with a modified Shin-Nippon NVision K5001 open-field autorefractor (Shin-Nippon, Tokyo, Japan). The subjects were asked to fixate on high contrast standard letter E (6/12 or 20/40) targets and red (650-680 nm) diode laser elliptical spots (3.75 mm spot width) at a viewing distance of 2.5 m. Each subject was measured at 0°, 20°, 30° and 40° eccentricities both nasally and temporally. Each measurement was repeated three times. From the refractive data, mean sphere (M) and cylinder/astigmatism (C) were analysed and compared using Bland-Altman analyses.
Average intra-session repeatability (standard deviation) for both target types was ±0.35D. The mean difference and standard deviation in M between the two measurement methods (laser target - letter target) for all measured eccentricities for right and left eyes were 0.03D ± 0.23D and 0.06D ± 0.25D respectively. The mean difference and standard deviation in C for right and left eyes were -0.06D ± 0.42D and -0.06D ± 0.24D respectively.
The results suggest no systematic difference between target types and measured refraction. Variability of results tended to increase with eccentricity suggesting differences between target types may be due to other factors (e.g. precision of alignment of eye).
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