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Thomas D. Raymond, Charles E. Campbell, David Baer; Comparison Of Repeatability Of Manifest Refraction And Instrument-based Refraction. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2820.
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© ARVO (1962-2015); The Authors (2016-present)
One method of measuring LASIK performance is by quoting the average and standard deviation of post-operative manifest refraction; however, the width of the outcome distributions is limited by the repeatability of the manifest refraction measurement. This retrospective study evaluates instrument-based refraction using the WaveScan and iDesign high resolution aberrometers to determine if a more accurate assessment of LASIK performance could be obtained by using objective refraction techniques.
Clinical aberrometer data from previous treatment and measurement-only studies were analyzed to assess the instrument based repeatability of sphere and cylinder measurements. These data comprised 981 pre operative and 799 six month post operative subject eyes as well as 98 virgin eyes measured on both aberrometers. At least one subjective and three instrument measurements were available for each eye. All available measurements were used to evaluate the ±95% bounds for repeatability of spherical equivalent power, cylinder power, compensated axis power, both cross cylinder components and vector blur power using a 4mm pupil diameter. In all cases, the narrower the 95% band the better the repeatability. These were compared to results for subjective refraction of virgin eyes from Bullimore (Optom Vis Sci 75(8) 617-22 1998) , Raasch (Opthal. Physiol. Opt. 21(5) 376-383 2001) and Zadnik (Invest. Ophtal Vis. Sci 33(7) 2325-2333 1992).
Table 1 lists the results of the statistical analysis of the objective refraction measurements from both instruments and the results reported by Bullimore and Raasch for subjective refraction repeatability of virgin eyes. In all cases, the objective refraction shows better repeatability compared to the subjective refraction.
The repeatability of the objective measurements is, in all cases including post operative measurements, better than the subjective measurements. We conclude that a more accurate assessment of LASIK performance could well be obtained by using pre and post operative objective measures of refraction rather than subjective measures.
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