To investigate the correlation between ocular residual astigmatism (ORA) and refractive and corneal astigmatism in refractive surgery candidates.

This cross-sectional study was conducted on 400 eyes of 200 patients who were referred to Farabi Hospital for refractive surgery. Preoperative examinations were performed for all candidates to measure refractive and corneal astigmatism. Ocular residual astigmatism was calculated using vector analysis. Both eyes were defined as cluster and the Generalized Estimating Equations analysis were performed.

Mean age of 125 women and 75 men was 28.2±6.24 years. Mean refractive astigmatism was 1.97±1.3 D in myopic and 1.3±1.37 D in hyperopic groups. Mean amount of ORA was 0.65± 0.36 D and 0.78±0.35 D in myopic and hyperopic groups, respectively. Mean corneal astigmatism was 1.8± 1.01 in myopic and 1.2± 1.12 D in hyperopic groups. There was a significant correlation between ORA and refractive astigmatism(r=0.22, p<0.001), corneal and refractive astigmatism (r=0.90, p<0.001) and weak correlations between ORA and corneal astigmatism (r=0.11, p=0.03).

There is a significant but weak correlation between ORA and refractive astigmatism and ORA and corneal astigmatism and strong correlation between both refractive and corneal astigmatism in refractive surgery candidates. Measurement of ocular residual astigmatism is highly recommended prior to any refractive surgery.