Improving the Refractive Accuracy of Cataract and Refractive Lens Exchange Surgery

Prospective Evaluation of the ESCRS Online Calculator for Calculation of a Multifocal Intraocular Lens

Lwowski C, Kohnen T¹
Industry support for this study: T.K., Consultant (Alcon/Novartis, Allergan, Bausch + Lomb, Carl Zeiss Meditec, Geuder, Johnson & Johnson, LensGen, Med Update, Oculentis, Oculus, Presbia, Santen, Schwind, STAAR Surgical, Thieme, Ziemer Ophthalmic Systems); Research support (Alcon/Novartis, Carl Zeiss Meditec, Johnson & Johnson, LensGen, Oculentis, Oculus, Presbia, Schwind)

ABSTRACT SUMMARY

This prospective consecutive case series of 88 eyes (88 patients) evaluated the accuracy of the ESCRS online IOL Calculator for a full-range of field (FRoF)^2,3 acrylic lens (PanOptix, Alcon) in femtosecond laser–assisted refractive lens exchange (RLE) and cataract surgery. The SRK/T formula was included for comparison.

The prediction errors (PEs) were calculated with each of the seven formulas available in the ESCRS IOL Calculator and the SRK/T. The main outcomes measured 3 months after surgery were the percentage of eyes with PEs within ±0.50 D, ±1.00 D, and ±2.00 D; mean PE; mean absolute error (MAE); and median absolute error (MedAE). The mean PE was slightly hyperopic for all ESCRS formulas (+0.01 to +0.08 D) but slightly myopic for the SRK/T (-0.08 D). The MedAE was similar with all formulas; there were no statistically significant differences between ESCRS IOL calculator formulas and the SRK/T, but the SRK/T showed the highest MedAE (0.31 D) compared with the ESCRS formulas (range, 0.26–0.30 D).

Although there were no statistically significant differences between the formulas regarding the percentage of eyes that had a PE within ±0.50 D, the accuracy of the ESCRS IOL Calculator formulas ranged from 78% to 84% (highest for the Hill-RBF), whereas the SRK/T showed 74% accuracy. The SRK/T had one outlier of -2.08 D, whereas other formulas had a PE of less than 0.28 D for that eye.

DISCUSSION

At the time of this writing, this was the only study to analyze the performance of the ESCRS IOL Calculator for an FRoF IOL power determination.

The use of multiple modern formulas helps to optimize IOL power selection and will likely supersede traditional formulas in the future.^4-9 Since October 2023, the ESCRS IOL Calculator has processed nearly 3 million calculations worldwide and has been used by approximately 100,000 surgeons globally.¹⁰ By extrapolation, each of these surgeons would have performed 30 IOL calculations on average over the course of nearly 2 years or 15 cases per year (assuming that only one calculation was performed per patient). Routine use of the ESCRS IOL Calculator therefore still is not widespread.

We have routinely used the ESCRS IOL Calculator in all our RLE and cataract procedures since 2023. We believe this has improved predictability, especially in complex cases^11,12 and with simultaneous vision IOLs.

The ESCRS IOL Calculator is the joint effort of many ophthalmologists. We expect that some empiric hurdles in its use (eg, automation and errors) will be solved as the website is further developed (Figure).

Comparison of the Accuracy of Toric Intraocular Lens Formulas Used by the Online Calculator of the European Society of Cataract and Refractive Surgeons

Liu C, Wang M, Long D, Zhang Y, Chen Y, Wu Q¹³
Industry support for this study: None

ABSTRACT SUMMARY

This retrospective case series of 85 eyes (85 patients) compared the accuracy of the ESCRS Toric IOL Calculator formulas (Kane, Emmetropia Verifying Optical [EVO] Toric v2.0, Hoffer QST, and Barrett with estimated posterior corneal astigmatism [EPCA]) for a toric, partial range of field, narrow (ie, monofocal) acrylic IOL (SN6AT2-9, Alcon) in cataract surgery to the Barrett toric IOL formula with directly measured posterior corneal astigmatism (MPCA). Outcomes measured 2 months after surgery were the percentage of eyes with a residual astigmatism PE within ±0.25 D, ±0.50 D, ±0.75 D, and ±1.00 D; mean PE; MAE; and MedAE.

In both the real-world analysis (using preoperative keratometry and desired toric IOL axis) and in the verification analysis (using postoperatively measured toric IOL axis), the Hoffer QST formula displayed the lowest MAEs in different astigmatism types, in medium and long eyes, and in eyes with medium keratometry readings. Overall, the EVO Toric Formula v2.0 showed the highest predictability (61.2% of eyes within ±0.50 D), followed by the Hoffer QST and Barrett EPCA. No significant differences between formulas were observed in eyes that had with-the-rule astigmatism. In eyes that had against-the-rule astigmatism, however, the EVO Toric Formula v2.0 performed the best.

Despite the statistically significant differences observed across many comparisons, the clinical significance of those differences was minimal.

DISCUSSION

We believe that the formulas incorporated in the ESCRS Toric IOL Calculator represent the highest scientific standard according to the most relevant available evidence published in the peer-reviewed literature. This study is the first to analyze the accuracy of the ESCRS Toric IOL Calculator. In the study, all the formulas showed similar clinical accuracy, although the predictability of the EVO Toric Formula v2.0 and the Hoffer QST formula tended to be favored. Using directly MPCA was not found to be superior to estimating it—in line with other research showing that EPCA was generally comparable to MPCA in regular clinical practice.^14,15

Importantly, even with a multiformula approach using modern IOL formulas, refractive predictability within ±0.50 D was achieved in only approximately 60% of eyes. This and similar studies show that there is a long way to go to improve postoperative astigmatic outcomes with toric IOLs.^16,17

One area for further research is an analysis of low cylinder—a major concern particularly in the setting of simultaneous vision toric IOLs (eg, enhanced monofocal, extended depth of focus, and multifocal IOLs) where greater than or equal to 0.75 D of residual astigmatism degrades quality of vision.^18-20 Another issue warranting further study is oblique astigmatism, where ESCRS formulas may suggest highly variable axes for IOL implantation, as shown in the Figure.

The authors offer their sincerest condolences to the family and Portuguese ophthalmology colleagues of Tiago Bravo Ferreira, MD, FEBOS-CR, PhD, who passed away in July 2025. Dr. Ferreira was a skilled refractive surgeon who developed relevant clinical research on the improvement of strategies for toric IOL power calculation.