Accuracy of the FY-L formula in calculating intraocular lens power after small-incision lenticule extraction

Yingfeng Hu; Liqun Lin; Danqi Zeng; Yan Wang; Rong Zhang; Zhe Zhang; Zheng Wang; Guangbin Zhang; Xiangyu Ye

doi:10.3389/fmed.2023.1241824

Accuracy of the FY-L formula in calculating intraocular lens power after small-incision lenticule extraction

Front Med (Lausanne). 2023 Aug 24:10:1241824. doi: 10.3389/fmed.2023.1241824. eCollection 2023.

Authors

Yingfeng Hu^#¹, Liqun Lin^#², Danqi Zeng³, Yan Wang¹, Rong Zhang¹, Zhe Zhang^{4

5}, Zheng Wang¹, Guangbin Zhang³, Xiangyu Ye^{1

3}

Affiliations

¹ Fuzhou Eye Hospital, Fuzhou, Fujian, China.
² Xianyou County General Hospital, Putian, Fujian, China.
³ Xiamen Eye Center, Xiamen University, Xiamen, Fujian, China.
⁴ Shenzhen Eye Hospital, Jinan University, Shenzhen, Guangdong, China.
⁵ Shenzhen Eye Institute, Shenzhen, Guangdong, China.

^# Contributed equally.

Abstract

Purpose: The study aimed to assess the accuracy of the FY-L formula in calculating intraocular lens (IOL) power after small-incision lenticule extraction (SMILE).

Methods: For the post-SMILE IOL calculation of the same eye, the IOL power targeting the pre-SMILE eyes' lowest myopic refractive error was used. The FY-L formula, the Emmetropia Verifying Optical Formula (EVO-L), the Barrett True-K no history, and the Shammas-L, respectively, were used to calculate the predicted refractive error of target IOL power. A comparison was made between the change in spherical equivalent induced by SMILE (SMILE-Dif) and the variance between IOL-Dif (IOL-Induced Refractive Error) before and after SMILE. The prediction error (PE) was defined as SMILE-Dif minus IOL-Dif. The proportion of eyes with PEs within ±0.25 D, ±0.50 D, ±0.75 D, and ±1.00 D, the numerical and absolute prediction errors (PEs and AEs), and the median absolute error (MedAE) were compared.

Results: In total, 80 eyes from 42 patients who underwent SMILE were included in the study. The FY-L formula generated the sample's lowest mean PE (0.06 ± 0.76 D), MAE (0.58 ± 0.50 D), and MedAE (0.47 D), respectively. The PEs in ±0.25 D, ±0.50 D, ±0.75 D, and ±1.00 D comprised 28.8%, 46.3%, 70.0%, and 87.5%, respectively, for the FY-L formula. Compared to other formulas, the FY-L formula produced the highest value with PEs for the percentage of eyes in ±0.50 D, ±0.75 D, and ±1.00 D.

Conclusion: This study demonstrates that the FY-L formula provides satisfactory outcomes in estimating the IOL power in the eyes after SMILE.

Keywords: FY-L formula; accuracy; intraocular lens power calculation; small-incision lenticule extraction; theoretical model.