Since, ORA is not calculated directly, it seems to have an special
importance in patients undergoing refractive surgery. However,
the relationship between ORA and other types of astigmatism is
not clear [14]. Many studies have evaluated the correlation
between refractive and corneal astigmatism and found that
refractive astigmatism is mainly corneal in origin [15–17].
However, results regarding the contribution of ORA have been
conflicting, with some studies finding a significant correlation
between ORA and total astigmatism in normal astigmats [15] and
others stating no significant relation between the two entities [18].
Astigmatism affects visual acuity and contrast sensitivity and
compared to other refractive errors, is more difficult to treat.
Additionally, with the advent of excimer laser techniques and the
unpredictability of visual outcome after laser refractive surgeries
in eyes with astigmatism [19] and lower efficiency of these
surgeries in correcting astigmatism that is mainly due to internal
optics of the eye [20], it is crucial to determine the pattern of
astigmatism and its components preoperatively. The purpose of
this study is to evaluate the correlation between refractive, corneal
and ocular residual astigmatism in patients undergoing refractive
surgery