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. 2014 Oct;40(10):1645-53.
doi: 10.1016/j.jcrs.2014.01.046. Epub 2014 Aug 29.

Influence of posterior corneal astigmatism on total corneal astigmatism in eyes with moderate to high astigmatism

Giacomo Savini  1 , Francesco Versaci  2 , Gabriele Vestri  2 , Pietro Ducoli  2 , Kristian Næser  2
Affiliations

Influence of posterior corneal astigmatism on total corneal astigmatism in eyes with moderate to high astigmatism

Giacomo Savini et al. J Cataract Refract Surg. 2014 Oct.

Abstract

Purpose: To evaluate the influence of posterior corneal astigmatism on total corneal astigmatism in patients with 1.00 diopter (D) or more of corneal astigmatism.

Setting: Private practice, Bologna, Italy.

Design: Prospective case series.

Methods: Corneal astigmatism was measured using a Scheimpflug camera combined with a corneal topographer (Sirius). Keratometric astigmatism, anterior corneal astigmatism, posterior corneal astigmatism, and total corneal astigmatism were evaluated. Vector analysis was performed according to the Næser method.

Results: One hundred fifty-seven eyes were enrolled. Keratometric astigmatism was with the rule (WTR), against the rule (ATR), and oblique in 84.0%, 11.5%, and 4.5% of eyes, respectively. Posterior corneal astigmatism exceeded 0.50 D and 1.00 D in 55.4% of eyes and 5.7% of eyes, respectively. The mean posterior corneal astigmatism was 0.54 D, inclined 91 degrees in relation to the steeper anterior corneal meridian. The steepest meridian was vertically aligned in 93.0% of cases. Compared with total corneal astigmatism, keratometric astigmatism overestimated WTR astigmatism by a mean of 0.22 D ± 0.32 (SD), underestimated ATR astigmatism by 0.21 ± 0.26 D, and overestimated oblique astigmatism by 0.13 ± 0.37 D. In the whole sample, a difference in astigmatism magnitude of 0.50 D or more was detected between keratometric astigmatism and total corneal astigmatism in 16.6% of cases and the difference in the location of the steep meridian was greater than 10 degrees in 3.8% of cases.

Conclusion: In patients who are candidates for surgical correction of astigmatism, measuring only the anterior corneal curvature can lead to inaccurate evaluation of the total corneal astigmatism.

Financial disclosure: Mr. Versaci and Mr. Vestri are employees of Costruzione Strumenti Oftalmici Srl. No author has a financial or proprietary interest in any material or method mentioned.

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