Surgically induced astigmatism made easy: calculating the surgically induced change in sphere and cylinder for corneal incisional, corneal laser, and intraocular lens-based surgery.

Net cylinder and spherocylinder formats characterize individual keratometries and prescriptions but must be converted to dioptric vectors to allow for calculations and statistical analyses. Næser's polar value system was specifically developed for the analysis of the surgically induced refractive change along the surgical meridian. This study provides a short description together with a practical manual and a computer program for the use of this dioptric vector method. Measurement techniques, vector equations, statistical methods, and terminology are reviewed. The analysis is identical for corneal and refractive measurements and for corneal incisional, corneal laser, and intraocular lens-based surgery. The choice of appropriate surgical reference meridians for standard surgical procedures is demonstrated. The Excel file may be used by the reader for future studies.