Astigmatism Notation: Dealing with Vectors

Net astigmatisms and spherocylinders are complex formats with magnitudes in diopters and directions in degrees. Both magnitudes and directions entities must be converted to vectors to allow for any kind of calculation. This chapter describes the principles for conversion of corneal and refractive data to dioptric vectors. Næser’s polar value dioptric vectors are detailed and other dioptric vector formats (Thibos, Holladay and Lang’s power matrix) are reviewed. The appropriate statistical methods for univariate and bivariate analysis are described, a terminology is suggested, and practical calculations are demonstrated.