PERIPHERAL ASTIGMATIC ASYMMETRY AND ANGLE-ALPHA

The association between peripheral astigmatic asymmetry and angle alph a was tested in the present study. Measurements were made in 34 eyes. Peripheral astigmatism was measured over the horizontal meridian using a Zeiss (Jena) Hartinger coincidence optometer and a Canon R-1 autore fractometer. Curves were fitted to the measured data of each eye and t he minima determined by differentiation. Angle alpha was estimated by alignment of Purkinje images I (anterior cornea) and IV (posterior cry stalline lens). Peripheral astigmatism was found to be symmetrical abo ut a point on the nasal retina. This point departed from the visual ax is by 8.8 +/- 7.0-degrees (Hartinger) and 9.4 +/- 9.8-degrees (Canon). Both values were found to be significantly higher than angle alpha 5. 0 +/- 1.2-degrees. The results indicate that either peripheral astigma tic asymmetry is due to additional factors such as lack of symmetry in the peripheral curvature of individual optical surfaces, or that ther e is further misalignment of optical surfaces away from an optical axi s.