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F. Barra, B. Antona, I. Sanchez, E. Gonzalez, A. Barrio, J. L. Cebrian; Repeatability and Agreement in the Accommodative Response Measurements. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1791.
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Clinical measurement of the accommodative response (AR) is an important part of the optometric exam because inappropriate responses, over- or under-accommodation relative to the plane of the stimulus, are a frequent cause of asthenopia. In order to demonstrate if a significant change in the AR has occurred, it is important to determine the degree of repeatability intra-examiner of this measurement. The aim of the present study was to compare the measurements of AR determined by using four different clinical methods, including the Nott retinoscopy, MEM retinoscopy, binocular cross cylinder (BCC) and autorrefractor at near. The hypothesis was that the degree of repeatability of the four methods would be quite different and that the four techniques could not be interchangeable.
The AR was measured on two separate occasions in 61 visually normal subjects with a mean age of 19.7 years (range 18 to 32 years). In each method, all measurements were recorded by the same examiner but different techniques were applied by different examiners who were blind to the AR measurements obtained by the other methods. The repeatability of the tests and the agreement between tests was estimated by using the statistical method of Bland y Altman. We determined the mean difference (MD), the standard deviation of the differences (SD) and the 95% limits of agreement, i.e. the range over which 95% of values would be predicted to lie (MD ± 1.96·SD). In all the methods it was computed the accommodative error, i.e. the difference between the stimulus and the AR.
The 95% limits of agreement for the accommodative error were: Nott: ±0.66 D; MEM: ±0.98 D; BCC: ±0.75 D and autorefractor: ±1.00 D. The Nott retinoscopy and the BCC methods presented the best repeatability intraexaminer, with the smaller MD (Nott: -0.10 D, BCC: -0.05 D) and the smaller 95% interval of agreement. Comparing different techniques, the intervals between the 95% limits of agreement correspond to substantial differences, always higher than ±0.75 D. The highest interval corresponds to the comparison of MEM retinoscopy with BCC (±1.38 D).
From the point of view of its repeatability intra-examiner, the best technique to evaluate the AR was the Nott retinoscopy. The degree of agreement between the four techniques was poor.
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