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      AI-Powered Effective Lens Position Prediction Improves the Accuracy of Existing Lens Formulas

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      research-article
      , BS 1 , , MD MS 2 , 3 , 4 , , MD 1 , 2
      medRxiv
      Cold Spring Harbor Laboratory

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          Abstract

          Aims:

          To assess whether incorporating a machine learning (ML) method for accurate prediction of postoperative anterior chamber depth (ACD) improves the refraction prediction performance of existing intraocular lens (IOL) calculation formulas.

          Methods:

          A dataset of 4806 cataract patients were gathered at the Kellogg Eye Center, University of Michigan, and split into a training set (80% of patients, 5761 eyes) and a testing set (20% of patients, 961 eyes). A previously developed ML-based method was used to predict the postoperative ACD based on preoperative biometry. This ML-based postoperative ACD was integrated into new effective lens position (ELP) predictions using regression models to rescale the ML output for each of four existing formulas (Haigis, Hoffer Q, Holladay, and SRK/T). The performance of the formulas with ML-modified ELP was compared using a testing dataset. Performance was measured by the mean absolute error (MAE) in refraction prediction.

          Results:

          When the ELP was replaced with a linear combination of the original ELP and the ML-predicted ELP, the MAEs ± SD (in Diopters) in the testing set were: 0.356 ± 0.329 for Haigis, 0.352 ± 0.319 for Hoffer Q, 0.371 ± 0.336 for Holladay, and 0.361 ± 0.331 for SRK/T which were significantly lower than those of the original formulas: 0.373 ± 0.328 for Haigis, 0.408 ± 0.337 for Hoffer Q, 0.384 ± 0.341 for Holladay, and 0.394 ± 0.351 for SRK/T.

          Conclusion:

          Using a more accurately predicted postoperative ACD significantly improves the prediction accuracy of four existing IOL power formulas.

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          Most cited references22

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          Sources of error in intraocular lens power calculation.

          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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            Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis.

            The precision of intraocular lens (IOL) calculation is essentially determined by the accuracy of the measurement of axial length. In addition to classical ultrasound biometry, partial coherence interferometry serves as a new optical method for axial length determination. A functional prototype from Carl Zeiss Jena implementing this principle was compared with immersion ultrasound biometry in our laboratory. In 108 patients attending the biometry laboratory for planning of cataract surgery, axial lengths were additionally measured optically. Whereas surgical decisions were based on ultrasound data, we used postoperative refraction measurements to calculate retrospectively what results would have been obtained if optical axial length data had been used for IOL calculation. For the translation of optical to geometrical lengths, five different conversion formulas were used, among them the relation which is built into the Zeiss IOL-Master. IOL calculation was carried out according to Haigis with and without optimization of constants. On the basis of ultrasound immersion data from our Grieshaber Biometric System (GBS), postoperative refraction after implantation of a Rayner IOL type 755 U was predicted correctly within +/- 1 D in 85.7% and within +/- 2 D in 99% of all cases. An analogous result was achieved with optical axial length data after suitable transformation of optical path lengths into geometrical distances. Partial coherence interferometry is a noncontact, user- and patient-friendly method for axial length determination and IOL planning with an accuracy comparable to that of high-precision immersion ultrasound.
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              The Hoffer Q formula: a comparison of theoretic and regression formulas.

              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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                Author and article information

                Journal
                medRxiv
                MEDRXIV
                medRxiv
                Cold Spring Harbor Laboratory
                03 November 2020
                : 2020.10.29.20222539
                Affiliations
                [1 ]Department of Computational Medicine and Bioinformatics, University of Michigan
                [2 ]Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan
                [3 ]Center for Eye Policy and Innovation, University of Michigan, Ann Arbor, MI
                [4 ]Department of Health Management and Policy, University of Michigan School of Public Health, Ann Arbor, MI
                Author notes

                CONTRIBUTIONS

                TL: data analysis, programming, and writing of the manuscript; JDS: data collection; NN: data collection, guidance on method development, and writing of the manuscript

                Corresponding Author: Nambi Nallasamy, MD, Kellogg Eye Center, University of Michigan, 1000 Wall St, Ann Arbor, MI 48105, Phone: (734) 763-5506, Fax: (734) 936-2340
                Article
                10.1101/2020.10.29.20222539
                7654911
                33173915
                03f000e8-4586-4f85-ad35-02bec462df60

                It is made available under a CC-BY-NC-ND 4.0 International license.

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