Intraocular lens power calculation: the contribute of angle kappa and ocular biomechanics

Abstract

Abstract Purpose: The effective lens position depends not only in static biometry but also on the dynamic interaction of the lens bag with the remaining ocular structures during the postoperative period. Our purpose was to study the effect of ocular biomechanics on the prediction error of IOL power calculation. Setting: Ophthalmology Department, Centro Hospitalar Universitário do Porto, Portugal. Design: Prospective longitudinal study. Materials: Before cataract surgery subjects underwent biometry with IOL Master® 700 (Zeiss, Germany) and biomechanical analysis with Corvis Scheimpflug Technology® (Oculus, Germany). The targeted spherical equivalent was calculated with SRK-T and Barrett Universal II. Associations between prediction error (PE), absolute prediction error (AE) and biometric and biomechanical parameters were performed with stepwise multivariable linear correlation analysis. Results: This study included 67 subjects. Using the SRKT formula, there was association between PE and Corvis Biomechanical Index (CBI, B=-0.531, p=0.011) and between AE and the horizontal offset between the center of the pupil and the visual axis (angle kappa, B=-0.274, p=0.007). Considering the Barret Universal II formula, PE was independently associated with anterior chamber depth (B=-0.279, p=0.021) and CBI (B=-0.520, p=0.013) and AE was associated with angle kappa (B=-0.370, p=0.007). Conclusion: A large angle kappa may reduce the predictability of IOL power calculation. Ocular biomechanics likely influence the refractive outcomes after IOL implantation. This study shows that eyes with softer corneal biomechanics have more myopic prediction error. This may relate to anteriorization of the effective lens position. Dynamic measurements may be the way to progress into future formulas.