Comparison of Conventional Keratometry and Total Keratometry in Normal Eyes

Abstract

Purpose. The relationship between conventional keratometry and total keratometry has not been fully investigated. This study was aimed at conventional keratometry measured with the automated keratometer and total keratometry with the corneal tomographer in ophthalmologically normal subjects. Methods. We enrolled fifty eyes of 50 consecutive subjects (mean age±standard deviation, 34.9±8.0 years) who have no ophthalmologic diseases, other than refractive errors, with no history of ocular surgery. Conventional keratometry was measured with the automated keratometer. The total keratometry, the true net power (TNP), and the total corneal refractive power (TCRP) were measured with the Scheimpflug camera, and the real power (RP) was measured with anterior segment optical coherence tomography (As-OCT). Anterior keratometries (Km and AvgK) were also measured with the Scheimpflug camera and the As-OCT, respectively. Results. Conventional keratometry was 43.64±1.48 D, which was significantly higher than the TCRP (42.94±1.45 D, p=0.042), the TNP (42.13±1.37 D, p<0.001), and the RP (42.62±1.39 D, p=0.001, Dunnett’s test). We found significant correlations between conventional keratometry and each total corneal power (the TCRP (Pearson’s correlation coefficient r=0.986, p<0.001), the TNP (r=0.986, p<0.001), the RP (r=0.987, p<0.001), the Km (r=0.990, p<0.001), and the AvgK (r=0.991, p<0.001)). The intraclass correlations of conventional keratometry with the TCRP, the TNP, the RP, the Km, and the AvgK were 0.986, 0.983, 0.985, 0.990, and 0.990, respectively. We found no significant differences in the keratometric data measured with the automated keratometer, the Scheimpflug camera, and the As-OCT (ANOVA, p=0.729). Conclusions. Conventional keratometry was significantly larger than total keratometry, by approximately 0.70 to 1.52 D, in ophthalmologically normal subjects. By contrast, there were no significant differences in the keratometric data among the three devices. It is suggested that conventional keratometry overestimates the total corneal power in daily practice.

Clinical Outcomes, Contrast Sensitivity, Reading Performance and Patient Satisfaction Following Bilateral Implantation of AT LARA 829MP EDoF IOLs

“…Refractive predictability was excellent in our study, with a mean postoperative residual SE of −0.17 D at 12 months and 95% of the eyes being within ±0.5 D of the target value. This suggests that advanced, swept source-based optical biometry 26 and modern IOL calculation formulae, such as the Barrett TK formula 27 , 28 used in the present study, may help cataract refractive surgeons to improve their chances of achieving postoperative targets closer to emmetropia in the majority of their cases.…”

Comparison of total keratometry with corneal power measured by optical low-coherence reflectometry and placido-dual Scheimpflug system

“…There were no eyes with >0.5D astigmatism difference between the TK and ssOCT-K groups similar to that reported earlier. 23 Analysis of the vectors, as shown in Tables 5 and 6, showed great agreement between the astigmatism vector mean of TK and ss-OCT (difference of 0.09 ± 0.43), OCLR-K (difference of 0.06 ± 0.43), and TCP (difference of 0.06 ± 0.44). The comparison between TK and SimK (difference of 0.31 ± 0.73) showed poorer agreement though not statistically significant.…”

Application of total keratometry in ten intraocular lens power calculation formulas in highly myopic eyes

“…Even with continuously advanced IOL power calculation formulas, cataract surgery on highly myopic eyes often results in unexpected refractive outcomes [ 12 ]. Recent improvements in TK biometry have demonstrated benefits in IOL calculation [ 16 , 17 , 27 – 29 ], but few studies have demonstrated its potential in highly myopic eyes, especially for those without prior refractive surgeries [ 13 ]. In this study, we demonstrated that highly myopic eyes with thinner CCTs tend to have larger differences between TK and K methods, while the XGBoost enhancement calculator and RBF 3.0 formula, with either TK or K method, seemed to be the most promising options for IOL power calculation for this special population.…”

“…Accuracies of other new formulas such as Cooke K6 formula, and Emmetropia Verifying Optical (EVO 2.0) formulas, remained unknown in highly myopic eyes. Rare previous studies have compared the performance of IOL calculation formulas when applying the new TK over standard keratometry (K) values in normal AL eyes [ 15 , 16 ], or in all AL ranges [ 13 , 17 ], but few in long AL eyes.…”