Meridional analysis of with-the-rule astigmatism in Oklahoma Indians

Refraction and keratometry records were obtained for 142 consecutive with-the-rule astigmats and for 100 consecutive nonastigmats from W. W. Hastings Indian Health Service Hospital in Tahlequah, Oklahoma. Patients were 5 to 40 years of age. Patients with higher degrees of Indian ancestry were more common in the astigmatic group than in the spherical refraction group. An analysis of refractive error and keratometry by principal meridian was performed. The horizontal meridian refractive error in astigmats was most often near emmetropia. Compound myopic astigmatism and mixed astigmatism accounted for over 3/4 of the cases. The astigmats as a group had flatter corneas in the horizontal and steeper corneas in the vertical than the nonastigmats. Horizontal refractive errors and horizontal keratometry readings showed a weak but significant correlation in astigmats but not in nonastigmats.