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Sumith Perera, Hala M Ali; Effect of variation in keratometric readings on the astigmatic power calculation and angle of implantation for toric intraocular lens implants.. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4189.
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Common methods of calculating keratometric readings (Ks) are dependent on reflections from the tear film. Variations in the corneal tear film affect the repeatability of the K readings. The K readings are used to calculate the astigmatic power of the toric lenses and the accuracy of their measurement is essential for an ideal refractive outcome. This study aims to look at the variability in the astigmatic power of toric intraocular lens (IOL) implants due to K reading measurement variation.
Three successive keratometric readings were taken by the same trained and experienced technician using the IOLMaster partial coherence interferometry device (Version S.2, Carl Zeiss Meditech Dublin California) for 32 virgin eyes of successive patients due to undergo lens extraction surgery. The IOLMaster was calibrated before each examination and only Ks that were within the recommended range were included for averaging. Keratometric readings and spherical IOL powers from each of the three scans for each eye were fed into the online Alcon AcrySof IQ Toric IOL calculator and the value and axis of the astigmatic power was noted for each scan. The values for the first scan was considered to be the reference. and the variation of the power and axis from this, if any, were calculated for the other two scan
In 29.7% of cases the calculated toric power of the lens differed from the reference toric lens power calculated for that eye (range 0.5-2.25D). In addition in 12.5% of cases the axis of orientation differed by more than 10° (range 10-23°).
This study shows that measurement variability in K readings can introduce an error to the selection of toric implants and their positioning. We recommend that at least three separate keratometric values are obtained to select the best value to use in the calculation.
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