Accuracy of the Kane Formula for Intraocular Lens Power Calculation in Comparison with Existing Formulas: A Retrospective Review

Comparison of Different Intraocular Lens Power Calculation Formulas in Eyes With Primary Angle Closure

STUDY DESIGN

Prospective case series.

PRCIS

This prospective study determines which formulas can best predict the refractive outcome in patients with primary angle closure disease (PACD) after cataract surgery.

OBJECTIVE

To compare the accuracy of 6 intraocular lens power calculation formulas, Barrett Universal II (BU II), Haigis, Hoffer Q, Holladay I, Kane and SRK/T, in eyes with PACD.

PATIENTS AND METHODS

Patients diagnosed with PACD and cataracts and who met the indication for cataract surgery were enrolled in the study. Six intraocular lens power calculation formulas were used to calculate the refractive diopter. The percentage of eyes with prediction error (PE) within ±0.50 D and the median absolute PE were compared to determine the accuracy of different formulas in patients with PACD. Subgroup analysis was performed according to axial length (AL). The accuracy of BU II was compared between patients with PACD and patients with age-related cataracts.

RESULTS

One hundred five patients (105 eyes) with PACD and 35 patients (35 eyes) with age-related cataracts were enrolled in the study. Haigis, Kane, and BU II formula achieved a comparable outcome and outperformed over the other 3 formulas in patients with PACD. Subgroup analysis showed that the group with long AL has lower values of median absolute PE. PE was significantly positively correlated with AL and negatively correlated with relative lens position when calculated using BU II and Kane.

CONCLUSIONS

Haigis, Kane, and BU II formula achieved a comparable outcome and outperformed over the other 3 formulas in patients with PACD.

Accuracy of intraocular lens power calculation formulae for the Yamane technique of secondary fixation: a systematic review and meta-analysis

OBJECTIVE

This systematic review and meta-analysis aims to assess the refractive outcomes of the Yamane technique for intrascleral fixation of intraocular lenses (SF-IOL) and compare the predictive ability of the various intraocular lens power calculation formulae commonly used in conjunction with the technique.

METHODS

A literature search was conducted in the Medline, Scopus, and Cochrane Library databases for articles published from January 2014 to May 2023. Studies that met the predetermined inclusion criteria were included and subjected to analysis. The primary outcome evaluated was the refractive predictive error, defined as the difference between predicted refraction and post-operative manifest refraction.

RESULTS

Eleven studies met the inclusion criteria, with a cumulative sample size of 615 patients (mean age: 66.6 years). Various IOL formulae were used, with SRK/T being the most frequently adopted formula. The overall mean refractive predictive error for all formulae combined was -0.02 D, which was not statistically significant (p = 0.99). Subgroup analysis for individual formulae also showed no significant difference from predicted error for any formula (p > 0.05).

CONCLUSION

The Yamane technique for SF-IOL shows promising refractive outcomes, and the choice of IOL power calculation formula should be tailored based on patient characteristics and surgeon preference. No formula demonstrated superior predictive ability over others. Further research is needed to develop formulae specifically for eyes with secondary aphakia and poor capsular support.

Influencing factors of effective lens position in patients with Marfan syndrome and ectopia lentis

AIMS

The aim of this study was to analyse the effective lens position (ELP) in patients with Marfan syndrome (MFS) and ectopia lentis (EL).

METHODS

Patients with MFS undergoing lens removal and primary intraocular lens (IOL) implantation were enrolled in the study. The back-calculated ELP was obtained with the vergence formula and compared with the theoretical ELPs. The back-calculated ELP and ELP error were evaluated among demographic and biometric parameters, including axial length (AL), corneal curvature radius (CCR) and white-to-white (WTW).

RESULTS

A total of 292 eyes from 200 patients were included. The back-calculated ELP was lower in patients undergoing scleral-fixated IOL than those receiving in-the-bag IOL implantation (4.54 (IQR 3.65-5.20) mm vs 4.98 (IQR 4.56-5.67) mm, p<0.001). The theoretical ELP of the SRK/T formula exhibited the highest accuracy, with no difference from the back-calculated ELP in patients undergoing in-the-bag IOL implantation (5.11 (IQR 4.83-5.65) mm vs 4.98 (IQR 4.56-5.67) mm, p=0.209). The ELP errors demonstrated significant correlations with refraction prediction error (PE): a 1 mm ELP error led to PE of 2.42D (AL<22 mm), 1.47D (22 mm≤AL<26 mm) and 0.54D (AL≥26 mm). Multivariate analysis revealed significant correlations of ELP with AL (b=0.43, p<0.001), CCR (b=-0.85, p<0.001) and WTW (b=0.41, p=0.004).

CONCLUSION

This study provides novel insights into the origin of PE in patients with MFS and EL and potentially refines existing formulas.

Analysis of accuracy of twelve intraocular lens power calculation formulas for eyes with axial hyperopia

PURPOSE

The purpose was to compare twelve intraocular lens power calculation formulas for eyes smaller than 22.0 mm in terms of absolute error (AE), the percentage of postoperative emmetropia, and agreement interval in Bland-Altman analysis.

METHODS

The data of hyperopic patients who underwent uneventful phacoemulsification between January 2016 and July 2021 were reviewed. Intraocular lens power was calculated using Holladay 1, SRK/T, Hoffer Q, Holladay 2, Haigis, Barrett Universal II, Hill-RBF, Ladas, Kane, Emmetropia Verifying Optical (EVO), Pearl-DGS, and K6 formulas. Three months after phacoemulsification, refraction was measured, and the mean AE was calculated. The percentage of patients with full visual acuity (VA) without any correction, with ± 0.25D, ±0.5D, ±0.75D, and limits of agreement for each formula was established.

RESULTS

Seventy-two patients, whose ocular axial length (AL) ranged between 20.02 mm and 21.98 mm, were included. The Kane formula achieved the lowest mean AE of 0.09 ± 0.09 just before EVO (0.12 ± 0.09), Hill-RBF (0.17 ± 0.12), and Hoffer Q formulas (0.19 ± 0.16). In addition, with the Kane formula, the percentage of patients with full VA without any correction (80.6%) was the highest ahead of EVO and Hoffer Q formulas (51.5% and 50.0%, respectively). Finally, Kane, EVO, and Hill-RBF obtained the lowest agreement interval (0.4923, 0.5815, and 0.7740, respectively).

CONCLUSION

The Kane formula is recommended for intraocular lens power calculation for eyeballs with the AL smaller than 22.0 mm. The EVO formula gives very promising results in regarding the accuracy of intraocular lens power for hyperopic eyes.

Refractive Outcomes of Non-Toric and Toric Intraocular Lenses in Mild, Moderate and Advanced Keratoconus: A Systematic Review and Meta-Analysis

Background: To perform a systematic review and meta-analysis of the refractive outcomes of non-toric and toric intraocular lenses (IOLs) in keratoconus (KC) using different IOL power calculation formulas. Methods: A systematic search was conducted to identify studies that report on refractive outcomes of different IOL power calculation formulas in KC patients undergoing cataract surgery. Inclusion criteria were primary posterior chamber non-toric and toric monofocal intraocular lens implantation, data on the degree of KC, explicit mention of the formula used for each stage of KC, and the number of eyes in each category. We calculated and compared the absolute and mean prediction errors, percentage of eyes within 0.5 D and 1 D from target, and the weighted absolute prediction errors of IOL formulas, all were given for KC degrees I–III. Results: The bibliographic search yielded 582 studies published between 1996 and 2020, 14 of which (in total 456 eyes) met the criteria: three studies on non-toric IOL (98 eyes), eight studies on toric IOLs (98 eyes) and three studies of unknown separation between non-toric and toric IOLs (260 eyes). The lowest absolute prediction error (APE) for mild, moderate, and advanced KC was seen with Kane’s IOL power formula with keratoconus adjustment. The APE for the top five IOL power formulas ranged 0.49–0.73 diopters (D) for mild (83–94%) of eyes within 1 D from the target), 1.08–1.21 D for moderate (51–57% within 1 D), and 1.44–2.86 D for advanced KC (12–48% within 1 D). Conclusions: Cataract surgery in eyes with mild-to-moderate KC generally achieves satisfactory postoperative refractive results. In patients with advanced KC, a minority of the eyes achieved spherical equivalent refraction within 1 D from the target. The Kane’s formula with keratoconus adjustment showed the best results in all KC stages.