To investigate the correlation of major components of ocular astigmatism in myopic patients in an academic hospital.

This cross-sectional study was conducted on 376 eyes of 188 patients who were referred to Farabi Eye Hospital for refractive surgery. Preoperative examinations including refraction and corneal topography were performed for all candidates to measure refractive and corneal astigmatism. Ocular residual astigmatism was calculated using vector analysis. Pearson's correlation and ANOVA analysis were used to evaluate the strength of the association between different types of astigmatism. Both eyes were defined as cluster and the Generalized Estimating Equations (GEE) analysis were performed.

Mean age of 119 women (63.3%) and 69 men (36.7%) was 27.8±5.7 years. Mean refractive error based on spherical equivalent was -3.59±1.95 D (range, -0.54 to -10.22 D).Mean refractive and corneal astigmatism was 1.97±1.3 D and 1.85± 1.01D, respectively. Mean amount of ORA was 0.65± 0.36 D. There was a significant correlation between ORA and refractive astigmatism(r=0.23, p<0.001), corneal and refractive astigmatism (r=0.91, p<0.001) and a weak correlation between ORA and corneal astigmatism (r=0.13, p=0.014).

There is a significant correlation between ORA and refractive astigmatism, refractive and corneal astigmatism and a weak correlation between ORA and corneal astigmatism in refractive surgery candidates. Identifying the type of astigmatism and preoperative measurement of ocular residual astigmatism is highly recommended prior to any refractive surgery, especially in cases with significant astigmatism.