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pubblicata il 03.10.2014

Savini, Giacomo, et al. "Influence of posterior corneal astigmatism on total corneal astigmatism in eyes with moderate to high astigmatism." Journal of Cataract & Refractive Surgery 40.10 (2014): 1645-1653.


Author information: From the Studio Oculistico d'Azeglio (Savini), Bologna, G.B. Bietti Eye Foundation I.R.C.C.S. (Ducoli), Rome, and Costruzione Strumenti Oftalmici Srl (Versaci, Vestri), Florence, Italy; School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University (Savini), Wenzhou, Zhejiang, China; Regions Hospital Randers (Næser), Randers, Denmark. Electronic address: giacomo.savini@alice.it. 2 From the Studio Oculistico d'Azeglio (Savini), Bologna, G.B. Bietti Eye Foundation I.R.C.C.S. (Ducoli), Rome, and Costruzione Strumenti Oftalmici Srl (Versaci, Vestri), Florence, Italy; School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University (Savini), Wenzhou, Zhejiang, China; Regions Hospital Randers (Næser), Randers, Denmark.

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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