Barrett True-K Formula Research Articles

Stability of the Barrett True-K formula for intraocular lens power calculation after SMILE in Chinese myopic eyes

To compare the Barrett True-K formula with other formulas integrated in Lenstar 900 to predict intraocular lens (IOL) power after small-incision lenticule extraction (SMILE). A theoretical prospective study was performed to predict the ratio of equivalent IOL power before and after SMILE using the SRK/T (Sanders, Retzlaff, Kraff/theoretical), Holladay 1, Haigis, and Barrett True-K formulas and compare the stability of their predictions. The study included 54 eyes (54 cases) with a manifest refraction spherical equivalent (MRSE) of -4.99±1.45 D. They were divided into two groups: 27 eyes with axial length of 24-26 mm in Group A, and 27 eyes with axial length >26 mm in Group B. All subjects enrolled in this study were examined with the Lenstar 900 before and 6mo after SMILE including measurements of axial length, corneal curvature, and anterior chamber depth (ACD). The prediction of equivalent IOL power of the two groups was more stable for the Barrett True-K formula, especially in long axial length eyes (Group B). The respective percentages for the SRK/T, Holladay 1, Haigis, and Barrett True-K formulas were 7.4%, 7.4%, 85.19%, and 88.89% for a margin of error within 0.5 D; 25.92%, 51.84%, 100%, and 100% for a margin of error within 1.0 D in Group A; 33.33%, 40.74%, 44.44%, and 81.48% for a margin of error within 0.5 D; and 44.44%, 59.26%, 66.66%, and 92.59% for a margin of error within 1.0 D in Group B. The respective percentages for Barrett True-K formulas were 100% for a margin of error within 2.0 D in Group B. Theoretically, the Barrett True-K formula provides more stable predictions than other formulas for cataract eyes after SMILE.

Results of the Barrett True-K formula for IOL power calculation based on Scheimpflug camera measurements in eyes with previous myopic excimer laser surgery.

To compare the refractive results of 4 different options for the Barrett True-K formula in eyes with previous myopic excimer laser surgery. IRCCS-Fondazione Bietti, Rome, Italy. Retrospective case series. Biometric measurements obtained with a rotating Scheimpflug camera (Pentacam) were entered into the Barrett True-K formula. Clinical history (laser-induced refractive change) and the measured posterior corneal curvature were entered as optional. Four variants of the Barrett True-K formula were investigated: (1) with history and measured posterior corneal power, (2) with history and predicted posterior corneal power, (3) no history with measured posterior corneal power, and (4) no history with predicted posterior corneal power. The prediction error (PE) was calculated as the difference between the measured and predicted postoperative refraction values. In 50 eyes (50 patients), the Barrett True-K formula with history and measured posterior corneal power resulted in the lowest standard deviation of the PE (0.52 diopters [D]), lowest median (0.245 D) and mean (0.413 D) absolute errors, and highest percentage of eyes with a PE within ±0.25 D (54%), ±0.50 D (70%), and ±0.75 D (84%). The Barrett True-K no-history formula with predicted posterior corneal power yielded the worst refractive outcomes. When the 4 options were compared, statistically significant differences were detected among the median absolute errors (P = .0017) and the percentage of eyes with a PE within ±0.25 D (P < .0001). Using historical data and measured posterior corneal power improved the refractive accuracy of the Barrett True-K formula in eyes with previous myopic excimer laser surgery.

Intraoperative Aberrometry Versus Preoperative Biometry for IOL Power Selection After Radial Keratotomy: A Prospective Study

To compare the accuracy of Optiwave Refractive Analysis (ORA) intraoperative aberrometry (Alcon Laboratories, Inc., Fort Worth, TX) with preoperative biometry in predicting residual refractive error after cataract surgery in eyes that underwent radial keratotomy. This was a prospective consecutive case series of patients with cataract and prior radial keratotomy. Each patient underwent a preoperative intraocular lens (IOL) power calculation using partial coherence interferometry (IOLMaster version 5; Carl Zeiss Meditec, Jena, Germany). For each eye, the Barrett True-K formula was used to select an IOL targeting emmetropia. Residual refractive error was predicted preoperatively using the SRK/T, Hoffer Q, Haigis, and Holladay formulas 1 and 2, and the ORA intraoperatively. Between 8 and 12 weeks after cataract extraction with IOL implantation, the postoperative refraction was compared with the preoperative and intraoperative predictions. The study comprised 52 eyes of 34 patients. The median absolute errors associated with each method were as follows: Barrett True-K formula (0.34), ORA aberrometer (0.53), and SRK/T (0.54), Hoffer Q (0.51), Haigis (0.54), SRK/T (0.57), and Holladay formulas 1 and 2 (0.44) (P = .08). The proportion of patients within ±0.50 diopters of the predicted error was 63.5%, 48.1%, 44.2%, 48.1%, 53.8%, 36.5%, and 57.7%, respectively (P = .03). No statistically significant difference was observed in the number of eyes with hyperopic outcomes (P = .68). In eyes with prior radial keratotomy surgery, the ORA aberrometer performance was similar to the Barrett True-K formula and all of the other established formulas, with no significant difference between median absolute error and mean absolute error. The Barrett True-K formula produced significantly more eyes within ±0.50 diopters than the SRK/T, Hoffer Q, and Holladay 1 formulas. [J Refract Surg. 2019;35(10):656-661.].

ASCRS calculator formula accuracy in multifocal intraocular lens implantation in hyperopic corneal refractive laser surgery eyes

To evaluate the accuracy of different intraocular lens (IOL) power calculation formulas available on the American Society of Cataract and Refractive Surgery calculator in calculating multifocal IOL power in eyes with previous hyperopic corneal refractive laser surgery. Retrospective case series. Amsterdam University Medical Center, University of Amsterdam, and Retina Total Eye Care, Driebergen, the Netherlands. This study compared the accuracy of 3 formulas using historical refractive data (ie, Masket, modified Masket, and Barrett True-K) and 3 formulas using no previous refractive data (ie, Shammas, Haigis-L, and Barrett True-K no-history). Sixty-four eyes were included. The variance of the prediction error of the various formulas was similar and ranged from 0.27 D2 to 0.33 D2 (P=.99). The modified Masket formula had a significantly higher median absolute prediction error than the Masket formula, Barrett True-K formula, and mean value of all formulas (P<.001). All formulas showed comparable accuracy in predicting IOL power in eyes after hyperopic corneal refractive laser surgery except for the modified Masket formula, which performed less accurately than the Masket formula, Barrett True-K formula, and mean value of all formulas.

Intraocular Lens Power Calculation after Refractive Surgery: A Comparative Analysis of Accuracy and Predictability.

To compare the accuracy of intraocular lens (IOL) power calculation using conventional regression formulae or the American Society of Cataract and Refractive Surgery (ASCRS) IOL power calculator for previous corneal refractive surgery. We retrospectively reviewed 96 eyes from 68 patients that had undergone cataract surgery after keratorefractive surgeries. We calculated the formula with two approaches: IOL powers using the ASCRS IOL power calculator and IOL powers using conventional formulae with previous refractive data (Camellin, Jarade, Savini, and clinical history method) or without prior data (0, 2 and, 4 mm total mean power in topography, Wang-Koch-Maloney, Shammas, Seitz, and Maloney). Two conventional IOL formulae (the SRK/T and the Hoffer Q) were calculated with the single K and double K methods. Mean arithmetic refractive error and mean absolute error were calculated at the first postoperative month. In conventional formulae, the Jarade method or the Seitz method, applied in the Hoffer Q formula with the single K or double K method, have the lowest prediction errors. The least prediction error was found in the Shammas-PL method in the ASCRS group. There was no statistically significant difference between the 10 lowest mean absolute error conventional methods, the Shammas-PL method and the Barrett True-K method calculated with using the ASCRS calculator, without using preoperative data. The Shammas-PL formula and the Barrett True-K formula, calculated with the ASCRS calculator, without using history, were methods comparable to the 10 most accurate conventional formulae. Other methods using the ASCRS calculator show a myopic tendency.

Accuracy of the Barrett True-K formula for intraocular lens power prediction after laser in situ keratomileusis or photorefractive keratectomy for myopia

To compare the accuracy of the Barrett True-K formula with other methods available on the American Society of Cataract and Refractive Surgery (ASCRS) post-refractive surgery intraocular lens (IOL) power calculator for the prediction of IOL power after previous myopic laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and private practice, Mesa, Arizona, USA. Retrospective case series. The accuracy of the Barrett True-K formula was compared with the Adjusted Atlas (4.0 mm zone), Masket, modified-Masket, Wang-Koch-Maloney, Shammas, and Haigis-L methods to calculate IOL power. A separate analysis of 2 no-history methods (Shammas and Haigis-L) was performed and compared with the Barrett True-K no-history option. Eighty-eight eyes were available for analysis. The Barrett True-K formula had a significantly smaller median absolute refraction prediction error than all other formulas except the Masket, smaller variances compared with the Wang-Koch-Maloney, Shammas, and Haigis-L, and a greater percentage of eyes within ±0.50 diopter (D) of predicted error in refraction compared with the Adjusted Atlas, Masket, and modified Masket methods (all P < .05). In eyes with no historical data, the Barrett True-K no-history formula had a significantly smaller median absolute refraction prediction error and a greater percentage of eyes within ±0.50 D of the predicted error in refraction than the Shammas and the Haigis-L formulas (both P < .05). The Barrett True-K formula was either equal to or better than alternative methods available on the ASCRS online calculator for predicting IOL power in eyes with previous myopic LASIK or PRK.

Comparison of Newer Intraocular Lens Power Calculation Methods for Eyes after Corneal Refractive Surgery

To compare the newer formulae, the optical coherence tomography (OCT)-based intraocular lens (IOL) power formula (OCT formula) and the Barrett True-K formula (True-K), with the methods on the American Society of Cataract and Refractive Surgery (ASCRS) calculator in eyes with previous myopic LASIK/photorefractive keratectomy (PRK). Prospective case series. A total of 104 eyes of 80 patients who had previous myopic LASIK/PRK and subsequent cataract surgery and IOL implantation. By using the actual refraction after cataract surgery as target refraction, predicted IOL power for each method was calculated. The IOL prediction error (PE) was obtained by subtracting the predicted IOL power from the power of the IOL implanted. Arithmetic IOL PEs, variances of mean arithmetic IOL PE, median refractive PE, and percent of eyes within 0.5 diopters (D) and 1.0 D of refractive PE. Optical coherence tomography produced smaller variance of IOL PE than did Wang-Koch-Maloney (WKM) and Shammas (P < 0.05). With the OCT, True-K No History, WKM, Shammas, Haigis-L, and Average of these 5 formulas, the median refractive PEs were 0.35 D, 0.42 D, 0.51 D, 0.48 D, 0.39 D, and 0.35 D, respectively, the percentage of eyes within 0.5 D of refractive PE were 68.3%, 58.7%, 50.0%, 52.9%, 55.8%, and 67.3%, respectively, and the percentage of eyes within 1.0 D of refractive PE were 92.3%, 90.4%, 86.9%, 88.5%, 90.4%, and 94.2%, respectively. The OCT formula had smaller refractive PE compared with the WKM and Shammas, and the Average approach produced significantly smaller refractive PE than all methods except OCT (all P < 0.05). The OCT and True-K No History are promising formulas. The ASCRS IOL calculator has been updated to include the OCT and Barrett True K formulas. Intraocular Lens Power Calculation After Laser Refractive Surgery Based on Optical Coherence Tomography (OCT IOL); Identifier: NCT00532051; www.ClinicalTrials.gov.