MULTIVARIATE-ANALYSIS VERSUS VECTOR ANALYSIS TO ASSESS SURGICALLY INDUCED ASTIGMATISM

Purpose: To present a multivariate probability computation method for assessing surgically induced astigmatism. Setting: Department of Ophth almology, Rennes University Hospital, Rennes School of Medicine, Franc e. Methods: The multivariate method was used to evaluate 100 patients who had cataract surgery by phacoemulsification. Keratometry was recor ded on the day before and 12 days after surgery. Surgically induced as tigmatism was assessed by the multivariate method as well as by most o f the published vector analysis methods. Results: The mean surgical in duced astigmatism (+/-SD) with the multivariate analysis was 1.18 +/- 0.36 diopters (D) for the cylinder power and 25.00 +/- 5.50 degrees fo r the cylinder axis. With the vector analyses, the mean surgically ind uced astigmatism was 1.67 +/- 0.54 D with the Naylor, Jaffe, and Holla day methods; 0.45 +/- 0.30 D with the latest Naeser method; 1.34 +/- 0 .38 D with the Cravy method (Cravy's vector); and -0.05 +/- 0.42 D for Cravy's delta K. Conclusion: Although Vector methods constitute inter esting geometrical models, their number and their lack of linearity an d explicit expression of results make them unsuitable for statistical analysis. Instead, a reliable, easily programmable method that uses ex isting software is recommended.