[Evaluation of the accuracy of modern intraocular lens calculation formulas when optical biometry is not possible]

PURPOSE

This study evaluates the accuracy of modern intraocular lens (IOL) calculation formulas using axial length (AL) data obtained by ultrasound biometry (UBM) compared to the third-generation SRK/T calculator.

MATERIAL AND METHODS

The study included 230 patients (267 eyes) with severe lens opacities that prevented optical biometry, who underwent phacoemulsification (PE) with IOL implantation. IOL power calculation according to the SRK/T formula was based on AL and anterior chamber depth obtained by UBM (Tomey Biometer Al-100) and keratometry on the Topcon KR 8800 autorefractometer. To adapt AL for new generation calculators - Barrett Universal II (BUII), Hill RBF ver. 3.0 (RBF), Kane and Ladas Super Formula (LSF) - the retinal thickness (0.20 mm) was added to the axial length determined by UBM, and then the optical power of the artificial lens was calculated. The mean error and its modulus value were used as criteria for the accuracy of IOL calculation.

RESULTS

A significant difference (p=0.008) in the mean IOL calculation error was found between the formulas. Pairwise analysis revealed differences between SRK/T (-0.32±0.58 D) and other formulas - BUII (-0.16±0.52 D; p=0.014), RBF (-0.17±0.51 D; p=0.024), Kane (-0.17±0.52 D; p=0.029), but not with the LSF calculator (-0.19±0.53 D; p=0.071). No significant differences between the formulas were found in terms of mean error modulus (p=0.238). New generation calculators showed a more frequent success in hitting target refraction (within ±1.00 D in more than 95% of cases) than the SRK/T formula (86%).

CONCLUSION

The proposed method of adding 0.20 mm to the AL determined by UBM allows using this parameter in modern IOL calculation formulas and improving the refractive results of PE, especially in eyes with non-standard anterior segment structure.

An evaluation of the accuracy of toric intraocular lens power calculation based on measured total corneal refractive power

Purpose

To evaluate a method using measured values of total corneal refractive power (TCRP) for a manufacturer's online calculator by comparing it with the Barrett toric calculator (BTC) and Kane toric calculator (KTC) combined with simulated keratometry values (SimK).

Methods

This was a retrospective case series. Patient records were reviewed to identify the patients who had biometry with the IOL Master 700 and Pentacam recorded before toric IOL implantation and refractive follow-up data after implantation. The predicted error in residual astigmatism was calculated by vector analysis according to the calculation methods and the measurements used.

Results

A total of 70 eyes of 56 patients were included. The mean absolute astigmatism prediction errors were 0.6 ± 0.32, 0.59 ± 0.35, and 0.61 ± 0.35 D for the ATC_TCRP, BTC_SimK, and KTC_SimK calculators, respectively (P = 0.934), and the centroid of the prediction errors were 0.3 D @ 178°, 0.11 D @ 102°, and 0.09 D @ 147°, respectively (P = 0.23). In the with-the-rule subgroup, the centroid of the prediction error was 0.34 D @ 176° for ATC_TCRP and was the highest among the three calculation methods (P = 0.046).

Conclusion

The ATC_TCRP, BTC_SimK, and KTC_SimK calculators had similar performance with regards to their astigmatism prediction accuracy. The ATC_TCRP calculator combined with 4.0-mm apex/ring readings of TCRP was slightly intended to result in against-the-rule residual astigmatism.

[Reasonability of accounting for gender in intraocular lens power calculation]

PURPOSE

The study assesses the influence of gender on the accuracy of intraocular lens (IOL) power calculation by formulas SRK/T, Barrett Universal II (BUII), Ladas super formula (LSF), Hill RBF (RBF) and Kane.

MATERIAL AND METHODS

The study enrolled 214 patients (106 men and 108 women) who underwent cataract phacoemulsification (PE). Optical biometry was performed on IOL-Master 500. IOL power calculation was performed either adjusting for gender (formulas SRK/T, BUII, LSF) or without such adjustment (formulas RBF, Kane). Calculation error (CE) was assessed one month after PE by comparing the achieved (autorefractometer Topcon-8800) and target spherical equivalent of refraction.

RESULTS

Significant differences were found in mean IOL CE with gender-unspecific formulas (SRK/T, BUII, LSF) and no differences in gender-specific calculators (RBF, Kane). The Kane formula demonstrated the lowest CE between men and women (-0.01±0.43 versus -0.09±0.41 D; p=0.158), while the SRK/T formula had the highest CE (0.02±0.46 versus -0.21±0.44 D, respectively; p<0.001). Presence of a significant correlation between CE and gender was found for all formulas except Kane (R2=0.005, p=0.158).

CONCLUSION

Patient's gender has a significant impact on IOL calculation accuracy. Using gender-responsive formulas could help achieve better refractive results with PE. The present study showed Kane formula to have the least CE dependence from gender. However, the CE difference (less than 0.25 D) was lower than the value of division (0.5D) in modern IOL models.

Accuracy of Six Intraocular Lens Power Calculations in Eyes with Axial Lengths Greater than 28.0 mm

The purpose of this study was to compare the accuracy of several intraocular (IOL) lens power calculation formulas in long eyes. This was a single-site retrospective consecutive case series that reviewed patients with axial lengths (AL) > 28.0 mm who underwent phacoemulsification. The Wang−Koch (WK) adjustment and Cooke-modified axial length (CMAL) adjustment were applied to Holladay 1 and SRK/T. The median absolute error (MedAE) and the percentage of eyes with prediction errors ±0.25 diopters (D), ±0.50 D, ±0.75 D, and ±1.00 D were used to analyze the formula’s accuracy. This study comprised a total of 35 eyes from 25 patients. The Kane formula had the lowest MedAE of all the formulas, but all were comparable except Holladay 1, which had a significantly lower prediction accuracy with either AL adjustment. The SRK/T formula with the CMAL adjustment had the highest accuracy in predicting the formula outcome within ±0.50 D. The newer formulas (BU-II, EVO, Hill-RBF version 3.0, and Kane) were all equally predictable in long eyes. The SRK/T formula with the CMAL adjustment was comparable to these newer formulas with better outcomes than the WK adjustment. The Holladay 1 with either AL adjustment had the lowest predictive accuracy.

Assessing Accuracy of Okulix Ray-Tracing Software in Calculating Intraocular Lens Power in the Long Cataractous Eyes

Purpose

To investigate the accuracy of Okulix ray-tracing software in calculating intraocular lens (IOL) power in the long cataractous eyes and comparing the results with those obtained from Kane, Holladay 1 with optimized constant, SRK/T with optimized constant, Haigis with optimized constant, and Barret Universal 2 formulas.

Methods

The present study evaluates the refractive results of cataract surgery in 85 eyes with axial length > 25 mm and no history of ocular surgery and corneal pathology. IOL power calculation was performed using the Okulix software. The performances of Okulix software in comparison with the five other formulas were evaluated by predicted error, mean absolute error, and mean numerical error 6 months after surgery.

Results

The mean calculated IOL power by the Okulix software was +13.48 ± 4.19 diopter (D). The mean of the 6-month postoperative sphere and spherical equivalent were +0.18 ± 0.63 and -0.34 ± 0.78 D, respectively. Also, the 6-month spherical equivalent in 56.6% and 80% of eyes were within ±0.05 and ±1.00 D, respectively. The predicted error (P < 0.001) and the mean numerical error (P < 0.001) were different between the six studied methods; however, we were not able to find any significant differences in the mean absolute error among six studied methods (P: 0.211).

Conclusion

The present study showed acceptable performance of the Okulix software in IOL power calculation in long eyes in comparison with the other five methods based on the postoperative refractive error, calculated mean absolute error, and mean numerical error.

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

PURPOSE

To evaluate the accuracy of the Kane formula for intraocular lens (IOL) power calculation in comparison with existing formulas by incorporating optional variables into calculation.

MATERIALS AND METHODS

This retrospective review consisted of 78 eyes of patients who had undergone uneventful phacoemulsification with intraocular implantation at Severance Hospital in Seoul, Korea between February 2020 and January 2021. The Kane formula was compared with six of the existing IOL formulas (SRK/T, Hoffer-Q, Haigis, Holladay1, Holladay2, Barrett Universal II) based on the mean absolute error (MAE), median absolute error (MedAE), and the percentages of eyes within prediction errors of ±0.25D, ±0.50D, and ±1.00D.

RESULTS

The Barrett Universal II formula demonstrated the lowest MAEs (0.26±0.17D), MedAEs (0.28D), and percentage of eyes within prediction errors of ±0.25D, ± 0.50D, and ±1.00D, although there was no statistically significant difference between Barrett Universal II-SRK/T (p=0.06), and Barrett Universal II-Kane formula (p<0.51). Following the Barrett Universal II formula, the Kane formula demonstrated the second most accurate formula with MAEs (0.30±0.19D) and MedAEs (0.28D). However, no statistical difference was shown between Kane-Barrett Universal II (p=0.51) and Kane-SRK/T (p=0.14).

CONCLUSION

Although slightly better refractory outcome was noted in the Barrett Universal II formula, the performance of the Kane formula in refractive prediction was comparable in IOL power calculation, marking its superiority over many conventional IOL formulas, such as HofferQ, Haigis, Holladay1, and Holladay2.