Comparing Refractive Prediction Accuracy Between Intraocular Lens Biometry And Holladay Equivalent Keratometry In Irregular Corneas

Hyperopic refractive error following cataract surgery in eyes with irregular corneas, such as those with keratoconus (KC) or prior penetrating keratoplasty (PKP) remains a limiting variable to optimizing post-operative visual outcomes. This study aims to evaluate whether incorporating both anterior and posterior corneal measurements using Holladay Equivalent Keratometry (EKR 65) enhances refractive prediction accuracy in comparison with Barrett True K and Kane formulas with keratoconus modification in KC and post-PKP eyes.

Ottawa Eye Institute, Faculty of Medicine, Department of Ophthalmology, University of Ottawa, Ottawa, Ontario, Canada

Single-center retrospective chart review included eyes with KC and prior PKP who underwent cataract extraction with monofocal intraocular lens (IOL) implantation between September 2015 and December 2023. Pre-operative keratometry from IOL Master biometry (SimK; IOLMaster 700) were applied to the Barrett True K keratoconus and Kane keratoconus formulas, while EKR 65 measurements from Pentacam Corneal Tomography (Scheimpflug EKR 65 at 4.5mm, 3.0mm, 2.5mm, 2.0mm optical zone) were applied to the Barrett Universal II formula to calculate predicted residual refraction (diopters, D). Primary outcome compared mean prediction error (PE) and mean absolute prediction error (MAE) among the three formulas. Data reported as mean ± standard deviation.

Forty-three eyes (26 PKP; 17 KC) from 34 patients with mean age of 64.8 ± 11.5 years were included. Mean flat and steep SimK keratometry values from IOL Master Biometry were 43.5 ± 2.8 D and 48.5 ± 3.5 D, respectively, and 43.5 ± 2.9 D and 47.0 ± 2.9 D from Holladay EKR 65, respectively. Mean PE was 0.63 ± 1.35 for Barrett True K and 0.73 ± 1.39 D for Kane, and 0.36 ± 1.56 D for Barrett Universal II groups. Subgroup analysis showed mean PE in KC patients was significantly different from zero (p=0.0325) only in the Kane group. MAE was lowest in Barrett True K (1.08 ± 1.02 D) as compared to Kane (1.21 ± 0.98 D) and Barrett Universal II (1.25 ± 0.98 D); however, no statistical differences were noted in overall or subgroup (KC, PKP) analysis.

The current findings suggest that in keratoconus and post-PKP eyes, Holladay EKR 65 is non-inferior to IOL Master SimK keratometry in corneas with moderate astigmatism. All three formulas demonstrated <1.0 D of mean prediction error, suggesting promising post-operative outcomes in irregular corneas. This study is limited by its retrospective nature and small-to-moderate astigmatism of the included eyes that may not fully represent all PKP and KC corneas. A future large-scale prospective study is warranted to confirm identified trends.