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A comparison of intraocular lens power calculation formulas in eyes with keratoconus

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First Author: J.Chaves PORTUGAL

Co Author(s):    J. Bernardes   M. Raimundo   J. Gil   C. Lobo   J. Murta        

Abstract Details


To comparatively evaluate the accuracy of newer intraocular lens (IOL) calculation formulas (Barrett Universal II, Kane, Ladas Super Formula AI, Hill-RBF 2.0, EVO, PhacoOptics®) and common second and third-generation formulas (SRKII, SRK/T, Haigis, Holladay 1) in the prediction of postoperative refraction in eyes with keratoconus (KC)


Tertiary university hospital


Retrospective study including eyes with stage 1 and 2 keratoconus (Amsler-Krumeich classification) submitted to uncomplicated cataract surgery. All patients underwent optical biometry (Carl Zeiss IOLMaster 500 and IOLMaster 700) and corneal tomography (Oculus Pentacam®) evaluation. The post-operative spherical equivalent for the same implanted IOL was estimated using SRKII, SRK/T, Holladay, Barrett Universal II, Kane, Ladas, Hill-RBF 2.0, EVO and PhacoOptics® formulas. Both IOL Master’s SimK and Pentacam’s 4.5-mm equivalent keratometry readings (EKR) values were used.Outcomes included the median absolute prediction error (MedAE) and the proportion of eyes within 0.50, 1.00 and 2.00 diopters (D) of the pre-operative prediction


Twenty-one eyes, 12 eyes with stage 1 KC (61.2%) and 9 eyes with stage 2 KC (42.8%), were included. When SimKs were used, MedAE was Hill-RBF 2.0 (0.64D), Kane (0.78D), EVO (0.96D), Barret (1.01D), SRK/T (1.32D), Ladas (1.34D), PhacoOptics (1.44D), Holladay 1 (1.63D), SRKII (1.84D). With 4.5-mm EKR, MedAE was Barret (0.93D), Haigis (0.95D), Kane (0.95D), Ladas (0.99D), Hill-RBF 2.0 (1.01D), EVO (1.06D), Holladay 1 (1.11D), SRK/T (1.14), PhacoOptics® (1.15D), SRKII (1.90D). The formula with the lowest MedAE, Hill-RBF 2.0, yielded a prediction error within 0.5D, 1D and 2D in 33.3%, 50% and 83.3% of cases, respectively.


To the best of our knowledge, this is the first study to evaluate the accuracy of recent “super-formulas” with eyes with keratoconus. As expected, eyes with keratoconus still represent a challenge regarding IOL power calculation due to unstable keratometry. Nonetheless, recent formulas like Barrett Universal II, Kane, Hill-RBF v2.0, Ladas Super Formula and EVO showed reasonably good accuracy, particularly when 4.5-mm EKR values were used. The Hill-RBF v2.0 formula had the lowest median absolute prediction error and highest proportion of eyes within 0.25D, 0.50D and 1.00D of the predicted target.

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