Theoretical Accuracy of the Raytracing Method for Intraocular Calculation of Lens Power in Myopic Eyes after Small Incision Extraction of the Lenticule

Abstract

Aim To evaluate the accuracy of the raytracing method for the calculation of intraocular lens (IOL) power in myopic eyes after small incision extraction of the lenticule (SMILE).

Methods Retrospective study. All patients undergoing surgery for myopic SMILE between May 1, 2020, and December 31, 2020, with Scheimpflug tomography optical biometry were eligible for inclusion. Manifest refraction was performed before and 6 months after refractive surgery. One eye from each patient was included in the final analysis. A theoretical model was invited to predict the accuracy of multiple methods of lens power calculation by comparing the IOL-induced refractive error at the corneal plane (IOL-Dif) and the SMILE-induced change of spherical equivalent (SMILE-Dif) before and after SMILE surgery. The prediction error (PE) was calculated as the difference between SMILE-Dif–IOL-Dif. IOL power calculations were performed using raytracing (Olsen Raytracing, Pentacam AXL, software version 1.22r05, Wetzlar, Germany) and other formulae with historical data (Barrett True-K, Double-K SRK/T, Masket, Modified Masket) and without historical data (Barrett True-K no history, Haigis-L, Hill Potvin Shammas PM, Shammas-PL) for the same IOL power and model. In addition, subgroup analysis was performed in different anterior chamber depths, axial lengths, back-to-front corneal radius ratio, keratometry, lens thickness, and preoperative spherical equivalents.

Results A total of 70 eyes of 70 patients were analyzed. The raytracing method had the smallest mean absolute PE (0.26 ± 0.24 D) and median absolute PE (0.16 D), and also had the largest percentage of eyes within a PE of ± 0.25 D (64.3%), ± 0.50 D (81.4%), ± 0.75 D (95.7%), and ± 1.00 D (100.0%). The raytracing method was significantly better than Double-K SRK/T, Haigis, Haigis-L, and Shammas-PL formulae in postoperative refraction prediction (all p < 0.001), but not better than the following formulae: Barrett True-K (p = 0.314), Barrett True-K no history (p = 0.163), Masket (p = 1.0), Modified Masket (p = 0.806), and Hill Potvin Shammas PM (p = 0.286). Subgroup analysis showed that refractive outcomes exhibited no statistically significant differences in the raytracing method (all p < 0.05).

Conclusion Raytracing was the most accurate method in predicting target refraction and had a good consistency in calculating IOL power for myopic eyes after SMILE.

Zusammenfassung

Ziel Das Ziel dieser Studie war es, die Genauigkeit der Raytracing-Methode zur Berechnung der Intraokularlinsenstärke (IOL-Stärke) bei myopen Augen nach der SMILE-Operation (Small Incision Lenticule Extraction) zu bewerten.

Methoden Es handelt sich um eine retrospektive Studie. Alle Patienten, die sich zwischen dem 1. Mai 2020 und dem 31. Dezember 2020 einer SMILE-Operation aufgrund von Myopie unterzogen haben und bei denen eine Scheimpflug-Tomografie-Optikbiometrie durchgeführt wurde, waren für die Studie geeignet. Eine Manifestrefraktion wurde vor und 6 Monate nach der refraktiven Chirurgie durchgeführt. Ein Auge jedes Patienten wurde in die abschließende Analyse einbezogen. Ein theoretisches Modell wurde verwendet, um die Genauigkeit mehrerer Methoden zur Berechnung der Linsenstärke vorherzusagen, indem der IOL-induzierte Refraktionsfehler in der Hornhautebene (IOL-Dif) und die SMILE-induzierte Änderung des sphärischen Äquivalents (SMILE-Dif) vor und nach der SMILE-Operation verglichen wurden. Der Vorhersagefehler (PE) wurde als Differenz zwischen SMILE-Dif und IOL-Dif berechnet. Die IOL-Berechnungen wurden unter Verwendung von Raytracing (Olsen Raytracing, Pentacam AXL, Softwareversion 1.22r05, Wetzlar, Deutschland) und anderen Formeln mit historischen Daten (Barrett True-K, Double-K SRK/T, Masket, Modified Masket) sowie ohne historische Daten (Barrett True-K ohne Historie, Haigis-L, Hill Potvin Shammas PM, Shammas-PL) für dieselbe IOL-Stärke und dasselbe Modell durchgeführt. Darüber hinaus wurde eine Untergruppenanalyse in Bezug auf verschiedene Vorderkammertiefen, Achslängen, Verhältnis von Rück- zu Vorderkornealradius, Keratometrie, Linsendicke und präoperative sphärische Äquivalente durchgeführt.

Ergebnisse Insgesamt wurden 70 Augen von 70 Patienten analysiert. Die Raytracing-Methode hatte den kleinsten durchschnittlichen absoluten PE (0,26 ± 0,24 dpt) und den medianen absoluten PE (0,16 dpt) und hatte auch den größten Anteil an Augen mit einem PE von ± 0,25 dpt (64,3%), ± 0,50 dpt (81,4%), ± 0,75 dpt (95,7%) und ± 1,00 dpt (100,0%). Die Raytracing-Methode war signifikant besser als die Formeln Double-K SRK/T, Haigis, Haigis-L und Shammas-PL in der Vorhersage der postoperativen Refraktion (alle p < 0,001), aber nicht besser als die folgenden Formeln: Barrett True-K (p = 0,314), Barrett True-K ohne Historie (p = 0,163), Masket (p = 1,0), Modified Masket (p = 0,806) und Hill Potvin Shammas PM (p = 0,286). Die Untergruppenanalyse zeigte, dass die refraktiven Ergebnisse in der Raytracing-Methode keine statistisch signifikanten Unterschiede aufwiesen (alle p < 0,05).

Schlussfolgerung Raytracing war die genaueste Methode zur Vorhersage der Zielrefraktion und zeigte eine gute Konsistenz bei der Berechnung der IOL-Stärke für myope Augen nach SMILE.

Key words

IOL power calculation - SMILE - myopia - cataract - refractive surgery

Schlüsselwörter

Katarakt - refraktive Chirurgie - IOL-Stärkenberechnung

Publication History

Received: 31 December 2022

Accepted: 07 September 2023

Accepted Manuscript online:
18 September 2023

Article published online:
23 November 2023

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