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Y. Han, C. C. Chiu; Comparing Partial Coherence Interferometry and Immersion A-Scan Ultrasound for Intraocular Lens Calculation. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6104.
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(1) To compare the ocular axial length measured by immersion A-scan ultrasound and partial coherence interferometry (IOLMaster). (2) To compare the cornea keratometry (K) readings measured by the autokeratometer and the IOLMaster. (3) To compare the accuracy in predicting postoperative refraction determined by each method.
Ocular axial length was measured in 140 cataractous eyes in 129 patients using immersion ultrasound and optical biometry (IOLMaster, Zeiss). Cornea keratometry was measured in 120 cataractous eyes in 111 patients by using the auto-keratometer and the IOLMaster. The results from each measurement were compared. For 84 cataractous eyes, the Holladay IOL calculation formula was used to select the intraocular lens. Postoperative refraction was obtained at least one month after surgery. The spherical equivalent was then calculated and compared to the predicted refractive error based on either the axial length and keratometry readings determined by the IOLMaster or the axial length measured from immersion ultrasound combined with keratometry readings from the autokeratometer.
Although axial length measured by immersion ultrasonography and the IOLMaster are highly correlated (R square= 0.99, p value <0.001), on average the IOLMaster measured shorter axial length by 0.133 mm than immersion ultrasound (paired T-test, p value = 0.01). Corneal keratometry measured by the autokeratometer and the IOLMaster are also highly correlated (R2= 0.96, p value <0.001). However, on average, the IOLMaster measured steeper average keratometry than the autokeratometer by 1.335 diopter (paired T test, p value = 0.03). The percentage of eyes within +/- 0.5 diopter of predicted refractive error were 75.0% by using IOLMaster and 66.7% by using immersion A-scan ultrasound combined with the autokeratometer (p value = 0.019).
We found that, on average, the IOLMaster measures shorter axial length than immersion A-scan ultrasound, but steeper cornea keratometry readings than the autokeratometer. Mixing data from the IOLMaster, immersion A-scan, and autokeratometer in IOL calculations leads to inaccurate IOL power prediction.
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