Accuracy of Constant C for Ray Tracing: Assisted Intraocular Lens Power Calculation in Normal Ocular Axial Eyes

Abstract

Objective: To evaluate the effect of constant C for ray tracing-assisted intraocular lens (IOL) power calculation in patients with different refractive power, we compared the refractive outcome of the ray tracing method based on constant C and conventional IOL calculation. Methods: 215 eyes which underwent phacoemulsification and IOL implantation were enrolled in the study. According to the average corneal power, patients were divided into 3 groups: high corneal power (K >45 D) group, medium corneal power (43 ≤ K ≤ 45 D) group, and low corneal power (K <43 D) group. The predicted sphero-equivalent refractive outcome for the IOL power implanted at surgery was calculated using the ray tracing method, SRK/T, and Haigis formulas. Results: On the basis of the corneal refractive power, there were 65 eyes of K >45 D (30.23%), 96 eyes of 43 ≤ K ≤ 45 D (44.65%), and 54 eyes of K <43 D (25.12%). In general, the ray tracing group had the smallest value of mean absolute error (MAE) and mean error, and the proportions of eyes with absolute error (AE) <0.50 and <0.75 D were significantly higher than those of the other 2 formulas (p = 0.010). In each group, the value of MAE was smallest in the ray tracing group; for the proportions of AEs <0.50 and <0.75 D, the values in the ray tracing group were higher than those in the SRK/T and Haigis groups. Especially in the high and low corneal refractive groups, the proportion of AE <0.25 D was also obviously higher, but only in the low corneal refractive power group, and the difference was statistically significant (p = 0.006). Conclusions: Compared with the conventional formulas, C constant of the ray tracing-assisted IOL power calculation has more accuracy for the patients with different corneal refractive powers. Ray tracing could provide better guidance for IOL selection clinically.

Accuracy of seven intraocular lens power calculation formulas: according to corneal power

“…In comparison to other formulas, the Haigis formula performed the poorest. As in some previous studies [16,19,20], this formula was the least accurate for eyes with at corneal power and of medium AL. It is possible that such results can be explained in that this formula does not calculate with corneal power.…”

“…As a result of grouping according to the Km, the results of the medium corneal power subgroup (43 D ≤ Km < 46 D) did not demonstrate any signi cant difference between the formulas. Previous studies indicated that the accuracy of the third-and fourth-generation formulas were similar, but there have been few comparisons of the new formulas [19,20]. Our study showed that the accuracy of the new and old formulas was quite similar when they were used to predict the eyes with a normal corneal power range.…”

“…The Hoffer Q, SRK/T, Haigis, and BUII formulas did not display a high accuracy in eyes with steep corneal power [16][17][18].Taking into account both AL and corneal power, the Haigis formula provided accurate results [19].Only a few studies used the new-generation formulas, such as the Hill RBF and Olsen C formulas. There is a signi cant improvement in the accuracy of the new-generation formulas over the old ones [16,20].It is unclear whether the new generation of formulas will have better prediction accuracy in different corneal curvature ranges.…”

“…Corneal power plays an important role in the IOL power calculation as one of the essential ocular biometric parameters. Previous evidence from a large-sample study showed that extreme corneal power can impact the accuracy of IOL power calculation formulas [16][17][18][19][20]. Nevertheless, most of the studies conducted in the past compared the accuracy of the third-and fourth-generation formulas in the case of eyes with extreme corneal power.…”

Intraocular lens power calculation in virgin eyes: Accuracy of the Barrett Universal II formula and a Ray tracing software

“…18,19 For this reason, RT has been proposed as a solution to optimize IOL power calculations, especially in the most complicated cases. 20,21 However, the use of exact RT in eyes with normal ocular AL has not always demonstrated a clear benefit over paraxial formulas. 10,21 To our knowledge, this is the first study that compares the refractive outcomes of Sirius RT software with the Barrett Universal II formula for IOL power calculation in virgin eyes.…”