Free Papers

Search Title by author or title

Performance of Barrett Toric and emmetropic verifying optical calculators for astigmatism correction

Free Paper Details

First Author: S.Pantanelli USA

Co Author(s):                        

Abstract Details


The Barrett Toric Calculator (BTC) is a vergence based formula that takes into account the effect of the posterior cornea and is highly reliable in its recommendations regarding the correction of astigmatism at the time of cataract surgery. The Emmetropic Verifying Optical (EVO) is a new formula proposed for same purpose. The purpose of this study was to compare the performance of the BTC and EVO v2.0 with respect to spherical equivalent (SE) and refractive astigmatism (RA) predictions.


This was a retrospective analysis of data collected as part of a prospective clinical trial evaluating efficacy of astigmatism correction with a monofocal toric IOL (B&L EnVista MX60T).


Pre-operative biometry was used to predict post-operative SE and residual RA with the implanted IOL using 1) surgeon’s preferred method from the clinical trial; 2) BTC; and 3) EVO Toric v2.0. Post-operative SE and RA was compared to pre-operative SE and residual RA predictions. SE outcome measures included mean prediction error (MPE) and proportion within 0.5 D of predicted. A difference vector (DV) was calculated between manifest RA and predicted residual RA, and outcome measures included centroid of the DV, proportion of eyes with DV ≤ 0.5 and 1.0 D, and proportion in which each nomogram correctly predicted astigmatism orientation.


Comparison of calculators was based on 109 eyes. MPEs were 0.14, 0.12, and 0.11 D for the three aforementioned methods, respectively (p=0.0132). The proportion of eyes within 0.5 D of predicted were 71%, 78%, and 78%, respectively. Centroid of the DVs were 0.40 D x 178, 0.09 D x 102, and 0.10 D x 100, respectively. The proportion of eyes with a DV magnitude ≤ 0.5 and 1.0 D were 43% and 85%, 49% and 90%, and 49% and 91%, respectively. The proportion of eyes in which the predicted and RA orientation matched were 62%, 78%, and 77%, respectively.


The EVO Toric Calculator v2.0 had better SE and astigmatism prediction accuracy than the surgeon’s preferred methods from the prospective clinical trial. BTC and EVO Toric v2.0 appear to be equivalent with regards to their SE and astigmatism predictions.

Financial Disclosure:

... receives consulting fees, retainer, or contract payments from a company producing, developing or supplying the product or procedure presented

Back to Free Papers listing