A study of the axis of orientation of residual astigmatism.

The aim of this study was to determine the axis of orientation of residual astigmatism in a sample of human eyes applying the principle of astigmatic decomposition. Calculations were carried out on keratoscopic and refractive data collected from the right and left eyes of 70 subjects (37 male and 33 female students) of mixed race (including 25 Asians and 43 Caucasians). No statistically significant difference was found for mean levels of residual astigmatism measured in the right (0.46 DC x 98.2 degrees) and left (0.50 DC x 99.4 degrees) eyes. Residual astigmatism was predominantly against-the-rule (83% of right eyes and 66% of left eyes) and was within +/- 20 degrees of being perpendicularly disposed relative to the corneal astigmatic power axis in two thirds of the eyes measured. No statistically significant differences were found for either gender or race.