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D.M. Win–Hall, H. Stampka, A. Glasser; Clinical Accuracy of WR–5100K Autorefractor and ITrace Aberrometer Using Contact Lenses . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5847.
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© ARVO (1962-2015); The Authors (2016-present)
Objective measurement of accommodation in clinical practice is possible with open field autorefractors and aberrometers. Practical, clinical methods for verifying accuracy of these instruments are critical. In this study, the accuracy of the Grand Seiko WR–5100K (GS) and Tracey ITrace (IT) refraction measurements were compared using subjects with a range of uncorrected refractive errors and by inducing known amounts of defocus with soft contact lenses.
18 subjects, aged 24–41 years old (mean±SD: 30.3±5.74) participated. Subjects fixated a target at 6 m with one distance corrected eye. Three uncorrected distance refractions (0D) were measured in the occluded, contralateral eye. Vision was blocked in the measured eye with an opaque occluder behind the instrument (IT) and a visible block–IR pass filter in front of the eye (GS). The measured eye was then fitted with soft contact lenses of powers +3, +2, +1, and –1D to create a known spherical defocus. In addition, uncorrected distance refractions were measured while the subjects viewed 5 degrees nasally and temporally off axis to test how misalignment impacts refraction measurements.
Uncorrected refractive errors ranged from +4.25 to –7.75 at the corneal vertex. Initial testing of the IT with this protocol, identified an error of increasing cylinder with increasing spherical defocus and the instrument was returned and repaired. Soft contact lens power correlated with corrected spherical refraction in both instruments (slopes: –0.978 for GS and –1.053 for IT). Results from the two instruments were not significantly different from each other (F–test = 3.79; p=0.12). The mean difference in spherical refraction between the two instruments was 0.13D with a 95% confidence interval of 0.82D. The mean difference in cylinder was 0.20D with a 95% confidence interval of 0.80D. Mean difference of on– and off–axis uncorrected distance refractions was –0.17D and –0.08D for GS and 0.02D and 0.10D for the IT temporally and nasally respectively with 95% confidence interval of 0.92D and 0.57D for the GS and 0.82D and 0.54D for the IT.
This protocol identified a calibration error in the IT. Once corrected, spherical refraction measurements from the IT and the GS were comparable. Soft contact lens induced spherical defocus is a reliable, clinical method to evaluate instrument performance. Small off–axis misalignments do not significantly affect refraction measurement accuracy with these instruments. Clinical calibration protocols can ensure reliability and identify possible instrument inaccuracies.
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