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Joseph J.K. Ma, Alice Zhu; Comparative Measures of Corneal Power (CP) and Internal Astigmatism Utilizing Full-Gradient (FG) Topography, Placido-disk (PD) Topography, Scheimpflug Imaging (SI), Slit-Scan Imaging (SS), Anterior Segment Optical Coherence Topography (AO), Wavefront Aberrometry (WA) and Keratometry (A/AK) with 11 Different Devices. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2460.
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To assess the inter-device comparison and intra-device repeatability with respect to keratometry, wavefront aberrometry and astigmatism to derive measures of corneal power and internal astigmatism (IA) to ultimately improve the predictability of surgical intervention in premium refractive/cataract surgery.
The study analyzed the results of 18 eyes of 9 volunteer subjects that had undergone testing w/ 11 devices and manifest refraction (MR) were grouped into 15 different instrument measures (FG,PD1,PD2,PD3,PD4,SI1,SI2,SS, AO,WA1,WA2,K,AK1,AK2,MR) repeated 6 separate times. The data was analyzed with respect to both inter-device and intra-device comparisons. Paired T-tests were performed and co-relations both inter and intra-device were examined.
The variability (SD, range) of inter- and intra-device measures of astigmatic power (>0.5D), astigmatic axis and derived calculations of IA were inversely proportional to the magnitude of the mean measured anterior corneal astigmatism (ACA) (eg. FG axis,ACA>1.5D,avg SD 1.8°,CA 0.5-1.0D, avgSD 3.2°). Inter-device variability was fair between shared methodologies and generally not stat sig. or clinically sig (eg.PD1,PD2 p=0.2). However, there were significant differences in intra-device variability within technologies (eg SI1,S2, p=0.0001). There were significant differences in values derived from different methods (eg.FG,AK1 p=0.001). The order of intra-device variability in angle of astigmatism was from least to greatest FG<SI1,AK2,PD2<PD1<PD4,<AK1<SI2<PD3<K. Although CP derived from different technologies had good intra-device variability (eg.SI avg SD=0.1D), there is significant inter-device variability (p<0.01).
FG appears to have a small advantage with respect to repeatability with ACA axis. Posterior corneal astigmatism (PCA) as measured by various methods has poor correlation with IA derived from either WA1,WA2 or MR. There were significant differences in intra-device variability between instruments utilizing similar technology, thus caution should be used wrt assumptions of equivalence based on methodology. Further study is necessary to confirm the results of this preliminary study and to assess the clinical significance of these findings.
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