Prediction Accuracy of Total Keratometry Compared to Standard Keratometry Using Different Intraocular Lens Power Formulas

Abstract

PURPOSE: To compare the accuracy of intraocular lens (IOL) power calculation based on standard keratometry (K) and the new Total Keratometry (TK). METHODS: A post-hoc analysis of study data based on 145 pseudophakic astigmatic eyes was conducted. The absolute prediction error (APE) of spherical equivalent (SE) and cylinder (CYL) was calculated based on K and TK (including posterior corneal surface) data recorded 6 weeks after IOL implantation. APE was calculated as the difference between the postoperative refraction and the refractive error predicted by three classic IOL calculation methods (Haigis/Haigis-T, Barrett Universal II, Barrett Toric Calculator) and two new formulas developed for TK (Barrett TK Universal II, Barrett TK Toric). For APE in SE, the Haigis-T (K versus TK) and Barrett Universal II (K) versus Barrett TK Universal II (TK) were compared. For APE in CYL, the Haigis-T (K versus TK) and Barrett Toric Calculator (K) versus Barrett TK Toric formula (TK) were compared. RESULTS: Mean APE in SE and CYL was lower based on TK values compared to K, with a mean APE difference (K-TK) of 0.011 ± 0.107 diopters (D) (SE Haigis-T; 95% confidence interval [CI]:-0.004 to infinity), 0.016 ± 0.113 D (SE: Barrett Universal II versus Barrett TK Universal II; 95% CI: 0.0005 to infinity), 0.103 ± 0.173 D (CYL: Haigis-T; 95% CI: 0.0791 to infinity), and 0.020 ± 0.148 D (CYL: Barrett Toric versus Barrett TK Toric; 95% CI:-0.0002 to infinity). APE in SE was within ±0.50 D in 86% (Barrett TK Universal II) versus 84% (Barrett Universal II) of eyes. APE in CYL was within ±0.50 D in 58% (Haigis from TK) versus 44% (Haigis from K) of eyes. CONCLUSIONS: In comparison to standard K, a higher prediction accuracy can be expected by using TK values along with the two newly developed formulas. TK values are compatible with standard IOL power calculation formulas and existing optimized IOL constants.

Comparison of ocular biometric measurements in patients with cataract using three swept-source optical coherence tomography devices

“…This is in line with the study by Fisus et al [8] that the mean absolute difference was 0.04 D when comparing ANTE RION and IOLMaster 700. Regarding total keratometry, a better refractive outcome was achieved using total keratometry compared to conventional anterior keratometry in the calculation of IOLs for cataract surgery by IOLMaster 700 [14][15][16]. In addition, it is expected that more patients will undergo cataract surgery who have previously undergone refractive surgery; therefore, it will become more important to accurately measure total corneal power [15,17].…”

“…The discrepancy of the three devices in total keratometry could be caused by the different algorism for calculating total keratometry in each device [5,8,19]. IOLMaster 700 obtains anterior keratometry with 18 reflected spots in hexagonal patterns at three zones (1.5 mm, 2.5 mm, and 3.5 mm) and posterior keratometry with SS-OCT tomography [16,20]. Meanwhile, ANTERION and CASIA2 calculate anterior and total keratometry only with SS-OCT images (ANTE RION: 65 B-scans with 256 A-scans each; CASIA2: 16 B-scans with 800 A-scans each) [8,21].…”

Prediction accuracy of conventional and total keratometry for intraocular lens power calculation in femtosecond laser-assisted cataract surgery

“…Today, standard keratometry (K) relies purely on measurements of the anterior corneal surface, and even when the posterior corneal surface is taken into consideration, the refractive index of the posterior corneal surface has been mostly inferred by calculation based on model eyes or nomograms 1 . Therefore, recent studies have debated the addition of accurate posterior corneal measurements to formulas for calculating IOL in patients undergoing cataract surgery 2 , 3 .…”

Factors Affecting Prediction Error after Cataract Surgery with Implantation of Various Multifocal IOLs in Patients with Previous Refractive Laser Surgery

“…The Barrett True-K formula more accurately calculates IOL power, representing the curvature of the entire cornea by including the posterior corneal curvature measurement 6,11−13 . In clinical studies reporting the results of cataract surgery after corneal refractive laser surgery, IOL power calculation using total keratometry which considers both anterior and posterior corneal curvature showed better results than conventional calculation using only the anterior corneal curvature [14][15][16][17][18][19] . Additionally, Shammas-PL based on total keratometry measured with an IOLMaster 700 biometer showed improved accuracy compared to that based on anterior keratometry in clinical studies by Lawless et al and Yeo et.…”