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F. Barra, B. Antona, A. Barrio, E. González, I. Sánchez; Validity and Repeatability of Two Direct Comparison Tests of Aniseikonia . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5639.
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Purpose: The New Aniseikonia Test (NAT) is a traditional hand test to measure aniseikonia, but several studies have shown that this direct comparison test underestimates the aniseikonia level. The Aniseikonia Inspector (AI) is a new software product to measure aniseikonia using red/green anaglyphs too. This study was designed to determine if the AI and/or the NAT are efficient and precise instruments to detect and quantify aniseikonia easily. Methods: The sample was form by two groups of subjects: Subjects at risk of suffering aniseikonia because their anisometropia was at least 1.00 D (N=30) and a control group (N=45). We induced aniseikonia by calibrated size lenses in the control group and we studied the validity of both instruments by comparison between the induced magnification and the measured aniseikonia. We estimated the repeatability and the concordance between tests in the two groups of subjects by using the statistical method of Bland and Altman. Results: The NAT and the AI underestimated induced aniseikonia, the underestimation factor was bigger in the horizontal direction than in the vertical one. Repeatability was low in both tests: the bias were clinically irrelevant but the limits of concordance at 95% were close to ±2%. So that in a re–test of aniseikonia only changes above ±2% could be attributed to a true visual change and not to imprecision of instruments. There was not any systematic difference between both tests, but there were more cases where the measure with AI was bigger than with NAT. Results were similar in the normal subjects and in the group of anisometropes. Conclusions: We conclude that both instruments are not valid to measure aniseikonia.
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