New method for intraoperativeIOL power calculation without need for biometry and keratometry

Abstract

Abstract: : Purpose:To derive a new intraoperative approach to Intra–Ocular Lens (IOL) power calculation based solely on optical refractometry and independent of biometric measurements such as axial length and keratometry. Methods: 20 eyes of patients undergoing extra–capsular cataract extraction surgery were enrolled in a prospective efficacy trial at LAC–USC department of Ophthalmology. A new retinoscopic predictive method for IOL calculation was derived and compared to standard ocular biometry based on A–scan and keratometry. All patients underwent pre–operative examination and clear–cornea cataract extraction by three surgeons. In addition, perioperative aphakic automated retinoscopy with a portable Nikon Retinomax was obtained before lens implantation. Correlation analysis between the traditional emetropic IOL power calculation method and the retinoscopic predictive method was performed. Results:Intraoperative retinoscopic autorefraction was successfully obtained on all cases enrolled. The spherical equivalent of the refraction was calculated accordingly and was incorporated into a linear regression analysis to correlate with the standard biometrically–derived emetropic IOL power. A strong correlation was obtained with an R2=0.94 and a p–value=0.0000005 for the linear correlation coefficient. A slight increase in the correlation model was evidenced after correction for final post–operative refraction. A purely refractive algorithm was derived for the prediction of IOL power during cataract surgery. Conclusions:A new model for IOL power calculation is derived to predict the dioptric power of the implant without need for axial length and keratometry measurements. The aphakic retinoscopic predictive model is based on an empiric regression formula which shows strong correlation to conventional methodology. The model we describe is independent of traditional biometric parameters, and could be successfully employed in post–LASIK cases as well.

Keywords: cataract • refractive surgery: other technologies