Agreement Between Pentacam and Opd Videokeratography in Corneal Power and Axis Assessment

Objective:The objective of this study is to investigate the agreement between a rotating Scheimpflug camera i:e Pentacam, (ALLEGRO Oculyzer Version 1074; Allergo,Germany) and OPD Scan (Nidek ARK-1000,Nidek Co LTD,Japan) in measuring the corneal power and the axes of the sim K readings of normal eyes. Design: Case-control study. Participants: for 117 eyes ( of 64 Egyptian patients ),the mean corneal powers calculated by simulated keratometry (SimK) as well as their axes by OPD Scan were compared to those provided by the Pentacam .n Methods:The mean corneal powers calculated by simulated keratometry (SimK) as well as their axes by OPD Scan were compared to those provided by the Pentacam in the eyes under study. Specifically, the corneal power values of the Pentacam included in this analysis were the SimK (calculated using the measured anterior corneal radius and standard keratometric index of 1.3375).For the entire sample,the K1 ,K2 and mean K reading(D) for each patient by OPD and by Pentacam were subjected to statistical analysis including Mean value ,Standard deviation,Minimum value,maximal value,Correlation of the measurements by both machines and Student "t" test for comparison of the measurements between both machines.The power of the minus astigmatism for the entire sample by OPD and Pentacam was subjected to statistical analysis including : Mean value,Standard deviation,Minimum value,maximal value Correlation of the measurements by both machines and Student "t" for comparison of the measurements between both machines. Correlation and compatison (Student "t" test) of the axes of K1 (flattest meridian)and K2(steepest meridian ) for the entire sample by OPD and Pentacam was also performed.Correlation and compatison (Student "t" test) of the axis of K1(flattest meridian) by OPD and Pentacam with the axis of the minus cylinder by refraction for the entire sample was also performed.Correlation and compatison (Student "t" test) of the mean value of minus cylinder by OPD and Pentacam with the mean value of the minus cylinder by refraction for the entire sample was also performed.For Correlation and Comparison(Student "t" test) tests,the probability and significance levels of the results were denoted. Main Outcome Measures: K1 and K2 power and axis measurement by Pentacam and OPD in normal corneas of refractive surgery patients. Results:The mean values for K1,K2 & mean K by OPD were 43.33±1.54D, 44.83±1.56D & 44.08±1.46 D respectively and by Pentacam 43.12±1.50D, 44.62±1.58D & 43.91±1.44D respectively and there is a non significant difference and a highly significant correlation between both machines for these measures. For the power of the minus astigmatism(D), the mean value for entire sample by OPD was 1.52±1.01D & by Pentacam was 1.59D±1.04D and there is a non significant difference and a highly significant correlation between both machines. For the axes of K1&K2, there is a non significant difference and a highly significant correlation between both machines. A non significant difference and a highly significant correlation was found between axis of flattest meridian(K1) by OPD and Pentacam and the axis of minus cylinder by refraction for entire sample.And similarly, a non significant difference and a highly significant correlation was found between the mean value for minus cylinder by (OPD&Pentacam) and by refraction for entire sample. Conclusion:Pentacam is almost equally accurate and reliable compared to OPD in detection of power and axes of K readings in normal corneas and is a very useful tool for achieving accuracy in refractive surgery. Financial disclosure(s): The author has no proprietary or commercial interest in any of the materials discussed in this article