Effect of Segmented Optical Axial Length on the Performance of New-Generation Intraocular Lens Power Calculation Formulas in Extremely Long Eyes

Abstract

Purpose: To evaluate the performance of traditional vergence formulas with segmented axial length (AL) compared to traditional composite AL in extremely long eyes, and to determine whether the segmented AL can be extended to the new-generation formulas, including the Barrett Universal II, Emmetropia Verifying Optical 2.0 (EVO2), Hill-RBF 3.0 (Hill3), Kane, and Ladas Super formula (LSF) formulas in extremely long eyes.

Setting: National Hospital. Organization, Tokyo Medical Center, Japan.

Design: Retrospective case series.

Methods: Consecutive patients who underwent uncomplicated cataract surgery implanted with a three-piece intraocular lens between December 2015 and March 2021 were retrospectively reviewed. The composite AL was measured with a swept-source optical coherence tomography (SS-OCT) biometer using a mean refractive index. The segmented AL was calculated by summing the geometric lengths of the ocular segments (cornea, aqueous, lens, and vitreous) using multiple specific refractive indices based on the data obtained by the SS-OCT-based biometer. When refraction was measured at three months postoperatively, the median absolute errors (MedAEs) were calculated with two ALs for each formula.

Results: The study included 31 eyes of 22 patients. The segmented AL (30.45 ± 1.23 mm) was significantly shorter than the composite AL (30.71 ± 1.28 mm, p < 0.001). The MedAEs were significantly reduced when using segmented AL for SRK/T, Haigis, Hill3, and LSF, compared to those obtained using composite AL (0.38 vs. 0.62, 0.48 vs. 0.79, 0.50 vs. 0.90, 0.34 vs. 0.61, p < 0.001 for all formulas, respectively). On the contrary, the MedAE obtained by Kane with segmented AL was significantly worse compared to the one with composite AL (0.35 vs. 0.27, p = 0.03).

Conclusion: In extremely high myopic eyes, the segmented AL improves the performance of SRK/T, Haigis, Hill3, and LSF formulas compared to the composite AL, while the segmented AL worsens the prediction accuracy of the Kane formula.

Keywords: extremely long eye; new-generation IOL power calculation formulas; segmented axial length; swept-source optical coherence tomography-based biometer.

Figure 1

Bland–Altman plots of composite and segmented axial lengths. The limits of agreement (LOA) were set at ±1.96 × standard deviation. The thin solid black line indicates zero, the thick solid red line indicates the mean, and the dashed lines indicate the upper and lower limits of agreement. AL = axial length, RI = refractive index.

Figure 2

Box plots illustrating the numerical prediction errors in refraction with intraocular lens calculation formulas based on each axial length obtained using two different methods: (1) Com-AL, the traditional composite axial length displayed by the SS-OCT biometer; and (2) Seg-AL, the segmented axial length calculated using data from the SS-OCT biometer. The dashed line indicates a 0 value, and white circles mean outliers. D = diopters, EVO2 = Emmetropia Verifying Optical 2.0, Hill3.0 = Hill-RBF 3.0, LSF = Ladas Super formula. *** p < 0.001.

Figure 3

Box plots showing the absolute prediction errors in refraction with intraocular lens calculation formulas based on each axial length obtained by two different methods: (1) Com-AL, the traditional composite axial length displayed by the SS-OCT biometer; and (2) Seg-AL, the segmented axial length calculated using data from the SS-OCT biometer. D = diopters, EVO2 = Emmetropia Verifying Optical 2.0, Hill3.0 = Hill-RBF 3.0, LSF = Ladas Super formula. White circles indicate outliers. * p < 0.05, *** p < 0.001.

Figure 4

Stacked histogram showing percentage of eyes within ±0.25 diopter (D), ±0.50 D, ±0.75 D, ±1.0 D, and >1.0 D range of prediction error. Axial length measurements were calculated with two different methods: (1) Com-AL, the traditional composite axial length displayed by the SS-OCT biometer; and (2) Seg-AL, the segmented axial length calculated using data from the SS-OCT biometer. EVO2 = Emmetropia Verifying Optical 2.0, Hill3.0 = Hill-RBF 3.0, LSF = Ladas Super formula.