Purpose : To determine the association between astigmatism and spherical refractive error in a clinical population
Methods : In this cross-sectional study, 2,000 patients who presented to our optometry clinic were enrolled. All were tested for objective refraction with a Nidek AR-310A auto refractometer, and non-cycloplegic refraction. For those under 15 years of age, cycloplegic refraction was measured as well. Myopia and hyperopia were defined as a spherical power of -0.5 Diopter (D) or less and +0.5 D or greater, respectively. Astigmatism was defined as a cylinder power of ≥-0.5 D with-the-rule (WTR) astigmatism if the steep axis was 0±20°, against-the-rule (ATR) astigmatism if the steep 90±20°, and oblique if the axis was in between.
Results : The mean age of the participants in this study was 31.52±18.39 years, and 910 (45.5%) were male. The Mean cylinder power of the subjects with high myopia and high hyperopia was 1.92±0.25 and 1.48±0.19 D, respectively. The lowest prevalence of astigmatism was found in subjects with emmetropia (P<0.001). There was an age-related decrease in the prevalence of WTR astigmatism, and an increase in ATR and oblique astigmatism (P<0.001). Mean cylinder error in WTR, ATR, and oblique astigmatism groups was 1.59±1.24, 1.10±0.76, and 1.16±0.04 D, respectively (P<0.001), and absolute mean spherical error was 1.97±2.03, 1.49±1.54, and 1.68±1.71 D, respectively (P<0.001).
Conclusion : The results of this study indicated an association between astigmatism and spherical refractive error. Higher amounts of astigmatism were seen in subjects with high spherical ametropia. Astigmatism axis was related to the cylinder and spherical powers which were both higher in subjects with WTR than those with ATR and oblique astigmatisms. In those with ATR astigmatism with the refractive status was close to emmetropia.
Iranian Journal of Ophthalmology 201123(4):37-42 © 2011 by the Iranian Society of Ophthalmology