Polynomial curve fitting of the corneal profile in 2.2-mm corneal incision phacoemulsification

To model incisional axis and perpendicular corneal profile pattern changes in 2.2-mm corneal incision phacoemulsification.

Sixty-seven eyes of 67 patients were included in this prospective, interventional, before-after paired design study. Power vector components were obtained from keratometry (IOLMaster; Carl Zeiss Meditec, Göttingen, Germany) and topography corneal height data with the Pentacam HR (Oculus Optikgeräte, Wetzlar, Germany) preoperatively and at 6 months postoperatively. Second- to sixth-order curve fitting polynomial functions of the corneal profile in the incisional and perpendicular axes were created using Matlab (The Mathworks, Inc., Natick, MA). Multivariate regression analysis was run to study the influence of potential predictors. Correlation of changes in corneal elevation and corneal radius with astigmatic parameters was also obtained.

Significant changes occurred only in the J(0) (P = .004) and M (P = .001) parameters. R(2) was high with all of the fitted polynomials (0.98 to 0.99) and although the smallest root mean square error was obtained with sixth-degree polynomials (0.63 to 1.13), they were more badly conditioned and redundant than quadratic polynomials. Corneal flattening changes were obtained on axis, which was the most frequent pattern (n = 52, 77%), but were significantly larger in the incisional side than the non-incisional side (P = .001) and only coupled with perpendicular axis steepening in 23 patients. In the non-incisional side on axis, corneal steepening was a relatively frequent pattern (n = 22 patients, 33%). Predictors studied for profile pattern of change were only near significance. Corneal radius of curvature changes were significantly correlated with astigmatic parameters.

Polynomial curve fitting is adequate for corneal biomechanical modeling of curvature and profile changes in the incisional and perpendicular axes of a 2.2-mm incision for phacoemulsification.