Accuracy of intraocular lens power calculation using three optical biometry measurement devices: the OA-2000, Lenstar-LS900 and IOLMaster-500

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Abstract

<div class="section"> <a class="named-anchor" id="d8844159e164">  </a> <h5 class="section-title" id="d8844159e165">Purpose</h5> <p id="Par1">To compare ocular measurements of three optical biometry devices and their application in intraocular lens (IOL) power calculations. </p> </div><div class="section"> <a class="named-anchor" id="d8844159e169">  </a> <h5 class="section-title" id="d8844159e170">Methods</h5> <p id="Par2">One hundred and forty eyes which had undergone cataract extraction surgery with preoperative biometry with OA-2000, IOLMaster-500, and Lenstar-LS900 were enrolled. Biometry measurements of the three devices were compared. The deviation of the postoperative refraction from the preoperative refractive target was calculated with different formulas (Barrett Universal II, Hoffer Q, Holladay I, and SRK/T). Errors in the predicted astigmatism using the Barrett toric calculator were calculated for the toric IOLs. Additional 6465 eyes in which the IOLMaster-500 failed to measure axial length (AL) were reviewed. The percentage of successful measurements using the OA-2000 in those eyes was calculated. </p> </div><div class="section"> <a class="named-anchor" id="d8844159e174">  </a> <h5 class="section-title" id="d8844159e175">Results</h5> <p id="Par3">High agreement was found between the three devices for AL, anterior chamber depth, and average keratometry measurements (interclass correlation confidents: 1.000, 0.970, and 0.998, respectively, <i>P</i> < 0.001). The mean absolute prediction errors were similar using all formulas, ranging from 0.25 to 0.29 D, with no statistical significant difference between the three devices per each formula. The OA-2000 yielded a lower against-the-rule (ATR) centroid error in the predicted astigmatism than the IOLMaster-500 and Lenstar-LS900 (0.06 D ± 0.59 at 13.4° vs. 0.20 D ± 0.61 at 14.8° and 0.16 D ± 0.55 at 21.4°, respectively, <i>P</i> < 0.001, <i>X</i>-axis). Among 301 cases with unsuccessful AL readings using the IOLMaster-500, the OA-2000 had 284 (94.35%) successful measurements. </p> </div><div class="section"> <a class="named-anchor" id="d8844159e188">  </a> <h5 class="section-title" id="d8844159e189">Conclusions</h5> <p id="Par4">The OA-2000 measurements showed good agreement with those of the IOLMaster-500 and Lenstar-LS900. Our results may suggest a potential advantage of the OA-2000 device in toric IOLs calculations and AL measurement success rate. </p> </div>

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Most cited references 15

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Sources of error in intraocular lens power calculation.

N E Sverker Norrby (2008)

To identify and quantify sources of error in the refractive outcome of cataract surgery. AMO Groningen BV, Groningen, The Netherlands. Means and standard deviations (SDs) of parameters that influence refractive outcomes were taken or derived from the published literature to the extent available. To evaluate their influence on refraction, thick-lens ray tracing that allowed for asphericity was used. The numerical partial derivative of each parameter with respect to spectacle refraction was calculated. The product of the partial derivative and the SD for a parameter equates to its SD, expressed as spectacle diopters, which squared is the variance. The error contribution of a parameter is its variance relative to the sum of the variances of all parameters. Preoperative estimation of postoperative intraocular lens (IOL) position, postoperative refraction determination, and preoperative axial length (AL) measurement were the largest contributors of error (35%, 27%, and 17%, respectively), with a mean absolute error (MAE) of 0.6 diopter (D) for an eye of average dimensions. Pupil size variation in the population accounted for 8% of the error, and variability in IOL power, 1%. Improvement in refractive outcome requires better methods for predicting the postoperative IOL position. Measuring AL by partial coherence interferometry may be of benefit. Autorefraction increases precision in outcome measurement. Reducing these 3 major error sources with means available today reduces the MAE to 0.4 D. Using IOLs that compensate for the spherical aberration of the cornea would eliminate the influence of pupil size. Further improvement would require measuring the asphericity of the anterior surface and radius of the posterior surface of the cornea.

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The Hoffer Q formula: a comparison of theoretic and regression formulas.

Barry Hoffer (1993)

A new formula, the Hoffer Q, was developed to predict the pseudophakic anterior chamber depth (ACD) for theoretic intraocular lens (IOL) power formulas. It relies on a personalized ACD, axial length, and corneal curvature. In 180 eyes, the Q formula proved more accurate than those using a constant ACD (P < .0001) and equal (P = .63) to those using the actual postoperative measured ACD (which is not possible clinically). In 450 eyes of one style IOL implanted by one surgeon, the Hoffer Q formula was equal to the Holladay (P = .65) and SRK/T (P = .63) and more accurate than the SRK (P < .0001) and SRK II (P = .004) regression formulas using optimized personalization constants. The Hoffer Q formula may be clinically more accurate than the Holladay and SRK/T formulas in eyes shorter than 22.0 mm. Even the original nonpersonalized constant ACD Hoffer formula compared with SRK I (using the most valid possible optimized personal A-constant) has a better mean absolute error (0.56 versus 0.59) and a significantly better range of IOL prediction error (3.44 diopters [D] versus 7.31 D). The range of error of the Hoffer Q formula (3.59 D) was half that of SRK I (7.31 D). The highest IOL power errors in the 450 eyes were in the SRK II (3.14 D) and SRK I (6.14 D); the power error was 2.08 D using the Hoffer Q formula. The series using overall personalized ACD was more accurate than using an axial length subgroup personalized ACD in each axial length subgroup. The results strongly support replacing regression formulas with third-generation personalized theoretic formulas and carefully evaluating the Holladay, SRK/T, and Hoffer Q formulas.

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Development of the SRK/T intraocular lens implant power calculation formula.

A Retzlaff, Robert Sanders, M Tanofsky-Kraff (1990)

A new implant power calculation formula (SRK/T) was developed using the nonlinear terms of the theoretical formulas as its foundation but empirical regression methodology for optimization. Postoperative anterior chamber depth prediction, retinal thickness axial length correction, and corneal refractive index were systematically and interactively optimized using an iterative process on five data sets consisting of 1,677 posterior chamber lens cases. The new SRK/T formula performed slightly better than the Holladay, SRK II, Binkhorst, and Hoffer formulas, which was the expected result as any formula performs superiorly with the data from which it was derived. Comparative accuracy of this formula upon independent data sets is addressed in a follow-up report. The formula derived provides a primarily theoretical approach under the SRK umbrella of formulas and has the added advantage of being calculable using either SRK A-constants that have been empirically derived over the last nine years or using anterior chamber depth estimates.