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Novel measurement method quantifies corneal astigmatism
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A new method of quantifying corneal astigmatism offered a more accurate representation of manifest refractive cylinder compared to commonly used measurement methods, according to a study.
“An alternative measure of corneal astigmatism, known as CorT, corresponded better to manifest refractive cylinder than other commonly used measures. A hemidivisional CorT can also represent the nonorthogonal asymmetrical astigmatism in irregular corneas,” the study authors said.
The retrospective review included 971 eyes of 498 patients aged 19 to 64 years who had not undergone refractive surgery. The researchers employed a vectorially calculated parameter, corneal topographic astigmatism (CorT), and compared it to manual keratometry, simulated keratometry, corneal wavefront and paraxial curvature matching.
Based on the range of ocular residual astigmatism, mean differences between corneal and refractive astigmatism indicated that CorT represented manifest refractive cylinder more accurately than the other corneal astigmatism measures. The standard deviation for CorT was significantly less than for other measures of astigmatism (P < .001).
The CorT value was derived by combining the astigmatism values for each Placido ring with a vector summation.
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