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Sverker Norrby, Nino Hirnschall, Yutaro Nishi, Oliver Findl; Fluctuations in Corneal Curvature Limits Predictability of IOL Power Calculations. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6737.
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© ARVO (1962-2015); The Authors (2016-present)
Analyze changes of keratometry from preop to postop, and at two postop points in time, in conjunction with cataract surgery.
In a study to investigate the stability of two IOL models, keratometry was measured preop and 1 year and 2 years postop with Zeiss IOLMaster. The differences between the measurements were analyzed by the power vector method of Thibos. Statistical significance was assessed by mono-variate and tri-variate paired t-tests.
The changes from preop to 1 year postop, the so-called surgically induced change (SIC), was found to be in M –0.01±0.23 D (P=0.75), in J0 –0.06±0.27 D (P=0.06) and in J45 +0.04±0.26 D (P=0.14) with tri-variate P=0.65. From 1 year to 2 years the change was found to be in M –0.01±0.24 D (P=0.71), in J0 +0.01±0.23 D (P=0.70) and in J45 +0.01±0.16 D (P=0.61) with tri-variate P=0.82.
There is a slight amount of SIC in J0, which is borderline statistically significant. There is more random variation in J45 from pre- to postop than from 1 year to 2 years. Otherwise the random variation is of the same order of magnitude from pre- to postop as between the two postop times. Shammas and Chan (J Cataract Refract Surg 2010; 36:1474-1478) found similar variability at two preop points in time as we found postop (data put at our disposal for power vector analysis). The variability is likely not due to measurement error, but reflects natural fluctuations in corneal curvature. Shirayama et al. (Am J Ophthalmol 2009; 148:528-535) found a standard deviation of 0.04 D in repeat measurements with IOLMaster. The variability in keratometry has consequences for the achieveable predictability of IOL power calculations for both sphere and cylinder.
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