Correlation between Refractive, Corneal and Residual astigmatism in refractive surgery candidates

Background and

Astigmatism is a common optical dysfunction, effective on various visual outcomes and one of the important criteria of refractive surgery. The aim of present study was to evaluate the correlation between refractive, corneal and residual astigmatism in refractive surgery candidates.

In this cross-sectional descriptive, analytical study, 200 patients referred to the Farabi hospital, Iran, for refractive surgery were enrolled. Refraction survey and topography were done to determine refractive, corneal and residual astigmatism for all of participants and statistical analyses were performed.

Overall, 400 eyes of 200 subjects with the average age of 28.2 ± 6.24 participated in this study. 62.7% of cases were women. According to spherical equivalent, 94.2% were myope, 3.3% were hyprope and 78.9% had refractive astigmatism more than 0.75 D. Mean spherical equivalent refractive errors was -3.59 ± 1.95 D in myopic group and 2.72 ± 0.97 D in hyperopic group; mean astigmatism was 1.97 ± 1.3 D in myopic and 1.3 ± 1.37 D in hyperopic group. The correlation ratio was (r = 0.223) between lenticular and refractive astigmatism (P < 0.001), (r = 0.111) between lenticular and corneal astigmatism (P = 0.027), and (r = 0.942) between refractive and corneal astigmatism (P < 0.001).

Significant correlations were found between refractive, corneal, and residual astigmatism; there was a strong correlation between corneal and refractive astigmatism; and 81% of the changes in refractive astigmatism could be justified with corneal astigmatism changes. Separating the type of astigmatism and determining its origin (cornea or lens) could be helpful for refractive surgery.