Authors: Jingyi Ma, Sherif El-Defrawy, John Lloyd, Amandeep Rai

Purpose: Evolution of intraocular lens (IOL) power prediction formulas and development of new technologies have led to improved refractive outcomes in modern cataract surgery. Given recent advances, there is a parallel increase in patient expectations regarding refractive outcomes and achieving spectacle independence is a major factor of patient satisfaction. Intraoperative aberrometry is a new development which measures the refractive power of an aphakic eye intraoperatively and predicts the residual refractive error expected for specific IOL powers. This study aims to compare the accuracy of intraoperative aberrometry with seven formulas based on pre-operative biometry for predicting IOL power. 

Study Design: Consecutive, retrospective case series. This study follows the tenants of the Declaration of Helsinki and has been approved by the University of Toronto’s Research Ethics Board. 

Methods: Fifty-seven eyes underwent cataract extraction, by one of three surgeons, with monofocal and trifocal IOL implantation without previous PRK or LASIK. For each eye, an IOL power was selected based on pre-operative biometry measurements from the IOLMaster 500. The spherical equivalent (SE) was predicted pre-operatively with the Barrett Universal II, SRKT, Holladay I, Holladay II, Haigis, HofferQ, and Hill-RBF formulas and intraoperatively with wavefront aberrometry. For each formula, the absolute difference between the one month post-operative SE and the predicted SE was calculated to determine the prediction error. The proportion of eyes with a post-operative SE within 0.5D of the refractive target was also calculated. 

Results: The analysis included 37 eyes. Formulas with the lowest mean prediction error were intraoperative aberrometry (0.27D), Hill-RBF (0.30D), Haigis (0.31D), Barrett Universal II (0.31D), Holladay II (0.36D), Holladay I (0.38D), SRKT (0.38D), and HofferQ (0.42D). Formulas with the highest proportion of eyes within 0.5D of the refractive target were intraoperative aberrometry (85%), Barrett Universal II (85%), Hill-RBF (82%), Haigis (79%), Holladay II (79%), SRKT (74%), Holladay I (71%), and HofferQ (68%). In 56% of eyes, intraoperative aberrometry recommended a different IOL power than the surgeon previously chose. In 29% of eyes, the IOL power implanted differed from the pre-operative choice. 

Conclusions: Based on preliminary results, intraoperative aberrometry has a lower mean prediction error than pre-operative biometry formulas. Intraoperative aberrometry and the Barrett Universal II formula were equally effective at achieving a post-operative spherical equivalent within 0.5D of the refractive target. Data collection is ongoing and we hope to establish statistical significance with further results and larger sample sizes.