A Simplified Method to Minimize Systematic Bias of Single-Optimized Intraocular Lens Power Calculation Formulas

Damien Gatinel; Guillaume Debellemanière; Alain Saad; Radhika Rampat; Avi Wallerstein; Mathieu Gauvin; Jacques Malet

doi:10.1016/j.ajo.2023.05.005

A Simplified Method to Minimize Systematic Bias of Single-Optimized Intraocular Lens Power Calculation Formulas

Am J Ophthalmol. 2023 Sep:253:65-73. doi: 10.1016/j.ajo.2023.05.005. Epub 2023 May 6.

Authors

Damien Gatinel¹, Guillaume Debellemanière², Alain Saad², Radhika Rampat², Avi Wallerstein³, Mathieu Gauvin³, Jacques Malet²

Affiliations

¹ From the Hôpital Fondation Adolphe de Rothschild (D.G., G.D., A.S., R.R., J.M.), Anterior Segment and Refractive Surgery Department, Paris, France. Electronic address: gatinel@gmail.com.
² From the Hôpital Fondation Adolphe de Rothschild (D.G., G.D., A.S., R.R., J.M.), Anterior Segment and Refractive Surgery Department, Paris, France.
³ Department of Ophthalmology and Visual Sciences (A.W., M.G.), McGill University, Montreal, Quebec, Canada; LASIK MD (A.W., M.G.), Montreal, Quebec, Canada.

PMID: 37150337
DOI: 10.1016/j.ajo.2023.05.005

Abstract

Purpose: To provide a simplified method to optimize lens constants to zero the mean prediction error (ME) of an intraocular lens (IOL) calculation formula, without the need to program the formula itself, by exploring the influence of IOL and corneal power on the refractive impact of variations in effective lens position.

Design: Theoretical development of an optimized formula and retrospective clinical evaluation on documented datasets.

Methods: Retrospective data from 8878 patients with cataracts with pre- and postoperative measurements available using 4 IOL models and 6 IOL power calculation formulas were examined. A schematic eye model was used to study the impact of small variations in effective lens position (ELP) on the postoperative spherical equivalent (SE) refraction. The impact of keratometry (K) and IOL power (P) on SE was investigated. A theoretical thick lens model was used to devise a formula to zero the average prediction error of an IOL power calculation formula. This was achieved by incrementing the predicted ELP, which could then be translated into an increment in the IOL constant. This method was tested on documented real-life postoperative datasets, using different IOL models and single-constant optimized IOL calculation formulas.

Results: For small variations in ELP, there was an exponential relationship between IOL power and the resultant postoperative refractive variation. The ELP adjustment necessary to zero the ME equated to a ratio between the ME and the mean of the following expression: 0.0006^*(P²+2K^*P) on the considered datasets. The accuracy of the values obtained using this formula was confirmed on documented postoperative datasets, and on published and nonpublished formulas.

Conclusion: The proposed method allows surgeons without special expertise to optimize an IOL constant to nullify the ME on a documented dataset without coding the different formulas. The influence of individual eyes is proportional to the squared power of the implanted IOL.

MeSH terms

Bias
Biometry
Humans
Lenses, Intraocular*
Myopia* / surgery
Optics and Photonics
Phacoemulsification*
Refraction, Ocular
Retrospective Studies