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Kevin Yum, Dorothy Pham, Ahmad Al-Heeti, Jenny Baek, Samir I Sayegh, Optimal surgical outcomes group; Clinical Comparison of Keratometry Measurements between Automated Keratometer and Placido-Rings Based Topographer. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1627.
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© ARVO (1962-2015); The Authors (2016-present)
To compare keratometry (K) measurements and orientation of pre-operative cataract patients between the automated keratometry and Placido-rings based topography devices.
K-values of 55 pre-operative cataract patients (with a total of 61 eyes), ages ranging from 46 to 89 with the mean age of 68, were obtained using an automated keratometer (Humphrey Zeiss 599) and a Placido-rings based topographer (Topcon CA-200F). All patients were sequentially tested with the automated keratometer followed by the Placido-rings based topographer on the same day in order to minimize variability. Mean, standard deviation, and Lin’s concordance correlation coefficients (Lin et al. 2002) were calculated, and correlation graphs were plotted and analyzed. Each graph consisted of equivalent K-values obtained from both the keratometry and topography devices on two separate axes. Based on the Cataract Surgery Guidelines established by the Royal College of Ophthalmologists, we created an exclusion criterion for cataract patients with △K and orientation differences larger than ±1 diopter and ±20 degrees.
Our preliminary data demonstrated that inter-device concordance correlations were higher in Kflat (ρOD=0.9235, ρOS=0.9371), Ksteep (ρOD=0.9508, ρOS=0.9017), and Kmean (ρOD=0.9467, ρOS=0.9359) than in variables relevant to the computation of toric intraocular lenses, for example, Ksteep-orientation (ρOD=0.8867, ρOS=0.5894). 33 out of 61 patients met the criterion defined above.
While determining the correct Kmean measurement is important for proper spherical intraocular lens (spherical IOL) calculation, additional corneal astigmatism (△K; Ksteep - Kflat) and orientation or axis measurements are required for toric IOL calculation. Our moderately low inter-device concordance results prompt further experiments to test for the cause of discrepancy. Based on this preliminary analysis, we recommend a third keratometry device such as the IOL Master for better analysis and IOL power calculation.
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