Accuracy of Intraocular Lens Power Formulas Modified for Patients with Keratoconus

Abstract

Purpose: To assess the accuracy of intraocular lens (IOL) power formulas modified specifically for patients with keratoconus (Holladay 2 with keratoconus adjustment and Kane keratoconus formula) compared with normal IOL power formulas (Barrett Universal 2, Haigis, Hoffer Q, Holladay 1, Holladay 2, Kane, and SRK/T). Design: Retrospective consecutive case series. Participants: A total of 147 eyes of 147 patients with keratoconus. Methods: Data from patients with keratoconus who had preoperative IOLMaster biometry were included. A single eye per qualifying patient was randomly selected. The predicted refraction was calculated for each of the formulas and compared with the actual refractive outcome to give the prediction error. Subgroup analysis based on the steepest corneal power measured by biometry (stage 1: 48 diopters [D], stage 2: >48 D and 53 D, and stage 3: >53 D) was performed. Main Outcome Measure: Prediction error. Results: On the basis of the mean absolute prediction error (MAE), the formulas were ranked as follows: Kane keratoconus formula (0.81 D), SRK/T (1.00 D), Barrett Universal 2 (1.03 D), unmodified Kane (1.05 D), Holladay 1 (1.18 D), unmodified Holladay 2 (1.19 D), Haigis (1.22 D), Hoffer Q (1.30 D), and Holladay 2 with keratoconus adjustment (1.32 D). The Kane keratoconus formula had a statistically significant lower MAE compared with all formulas (P < 0.01). In stage 3 keratoconus, all nonmodified formulas had a hyperopic mean prediction error ranging from 1.72 to 3.02 D. Conclusions: The Kane keratoconus formula was the most accurate formula in this series. The SRK/T was the most accurate of the traditional IOL formulas. All normal IOL formulas resulted in hyperopic refractive outcomes that worsened as the corneal power increased. Suggestions for target refractive aims in each stage of keratoconus are given. Ophthalmology 2020;127:1037-1042 ª 2020 by the American Academy of Ophthalmology Keratoconus is a progressive disorder characterized by central or paracentral corneal thinning and ectasia. Intraocular lens (IOL) power calculation in these eyes represents a significant challenge. Kamiya et al 1 reported on 71 patients with keratoconus comparing the Haigis, Hoffer Q, Holladay 1, Holladay 2, and SRK/T formulas and found that that the SRK/T formula was the most accurate with 36% of eyes within 0.50 diopters (D) of the final manifest refraction. Savini et al 2 also found that the SRK/T was the most accurate formula in 41 patients (compared with Barrett Universal 2, Haigis, Hoffer Q, and Holladay 1), with 43.9% of eyes within 0.50 D. Both studies found that all formulas resulted in a hyperopic refractive surprise that worsened with more advanced stages of the disease. Suggestions regarding an appropriate myopic refractive target to avoid unwanted postoperative hyperopic error have been proposed. 3 These refractive results in keratoconus studies are significantly worse than the 75% to 80% of eyes within 0.50 D usually seen in nonkeratoconic eyes, 4 for which there are many reasons. First, the calc...

Repeatability and agreement of biometric measurements using spectral domain anterior segment optical coherence tomography and Scheimpflug tomography in keratoconus

“…Such patients present unique challenges for the cataract surgeon regarding intraocular lens (IOL) power calculation. The inherent difficulty in obtaining accurate biometric measurements, changes in the relationship between the anterior and posterior cornea, inaccurate calculation of the effective lens position due to inaccurate keratometry measurement, and axis of astigmatism [ 9 ] can result in unpredictable refractive outcomes [ 10 ]. Reduction of biometric measurement error can therefore optimize post-operative refractive and visual outcomes in patients with keratoconus.…”

Intraocular lens power calculation in patients with corneal ablative treatments or corneal pathologies: perspective

“…15 For SRK/T, adjustments to the target refraction are recommended to correct for errors in effective lens position prediction as follows: 0.75 to 1.5 diopters in stage II and 2.0 to 3.0 diopters in stage III. 16 Regarding lens design, toric lenses are a good option for correcting regular astigmatism. Nonetheless, in patients with keratoconus, the astigmatism is often irregular, which creates difficulties in both IOL calculation and IOL positioning.…”

Cataract surgery considerations in patients with prior history of keratoconus and ectasia

“…In a study by Wang et al [39], 40% of patients were within 0.5 D using Haigis. Kane et al [36] determined that 24% were within 0.5 D with Kane for keratoconus, and Savini et al [33] concluded that 14.3% of patients were within 0.5 D with Hoffer Q and SRK/T.…”