Ocular residual astigmatism (ORA) does not seem to correlate with baseline refractive error among refractive surgery candidates

Abstract

Purpose: Ocular residual astigmatism (ORA) is defined as the difference between refractive astigmatism and anterior corneal astigmatism. A high ORA may be correlated with poorer results in patients undergoing corneal-based laser surgery. Is a high baseline refractive error related to a higher degree of ORA?

Methods: This was a retrospective analytical study including 181 right eyes of an equal number of refractive surgery candidates. Manifest subjective refraction was measured, along with a Pentacam AXL Wave corneal tomography. Via a vector analysis with this methodology, subjective cylinder was translated into the corneal plane and a vectorial subtraction was performed in order to measure ORA. Spearman's rank order test, one-way ANOVA and Chi-square were used to determine whether different levels of baseline refractive error correlate with different levels of ORA.

Results: Mean age was 28.33 ± 4.71 years with a female preponderance (65.7%). Mean ORA was 0.74 ± 0.39 D, with 33.1% of eyes having an ORA ≥ 0.90 D. There was not a correlation between ORA and level of myopia (rho = - 0.022; p = 0.764), nor between ORA and spherical equivalent (rho = 0.009; p = 0.903). Refractive astigmatism did not demonstrate to be correlated with ORA level either (rho = 0.078; p = 0.329). One-way ANOVA tests failed to demonstrate an association between different classifications of refractive error and level of ORA.

Conclusions: In the studied population, ORA is not correlated with baseline refractive error. Every patient presenting for possible corneal-based laser refractive surgery should be evaluated for a possible high level of ORA, irrespective of their baseline ametropia level.

Keywords: Baseline refractive error; Corneal-based laser surgery; Ocular residual astigmatism; Refractive surgery.