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Jaime Tejedor, Antonio Guirao; Relationship Between Refractive And Corneal Astigmatism In Pseudophakic Eyes. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5901.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the relationship between refractive and corneal astigmatism in a population of pseudophakic eyes.
We included 111 of 128 pseudophakic patients (one eye per patient) operated by phacoemulsification, using 2.8-mm corneal incision. Refractive astigmatism was obtained by subjective refraction. Corneal astigmatism was measured by two different methods: keratometry and videokeratographic analysis (Pentacam, Oculus). All refractive values were converted to power vector components J0 and J45. Comparison and regression analysis of refractive versus corneal astigmatism components were carried out. The main outcome measure was refractive and corneal astigmatism components at 6 months postoperatively.
(A) Keratometric vs refractive data: vector J was lower in refractive (mean: 0.39 D, 95% CI: [0.33–0.45] D) than in corneal astigmatism (mean: 0.50 D, 95% CI: [0.44–0.55] D) (p< 0.01). J45 astigmatic component was nearly zero, and not significantly different, in refractive and corneal astigmatism. However, the refractive J0 component was negative, indicating against-the-rule (ATR) astigmatism (-0.11 D, 95% CI: [-0.03– -0.19] D) on average, compared with corneal J0, which was close to zero (0.03 D, 95% CI: [-0.05–0.12] D) (p< 0.01). Refractive and corneal J0 were significantly correlated (r= 0.71, p< 0.01; 95% CI for the slope: 0.49–0.72), as well as the corresponding J45 values (r= 0.72, p< 0.01; 95% CI for the slope: 0.53–0.76). (B) Pentacam vs refractive data: when anterior and posterior corneal values of Pentacam scanner were used, corneal and refractive components were similar, including corneal J0, which was negative (-0.1 D, 95% CI: [-0.27–0.07] D). Correlation between refractive and corneal J0 (r= 0.7, p< 0.01; 95%CI for the slope: 0.37–0.71), and between J45 values (r= 0.69, p< 0.01; 95%CI for the slope: 0.41–0.73) was essentially the same.
Mean internal ATR astigmatism counterbalances a small with-the-rule (WTR) corneal astigmatism, resulting frequently in ATR refractive astigmatism in pseudophakic eyes. The internal ATR astigmatism comes mainly from the posterior corneal surface. Correspondence between refractive and corneal astigmatism is better when posterior corneal data are incorporated to the analysis. Regression lines between refractive and corneal astigmatism components, and equations that simulate a vector-based Javal’s rule for pseudophakic eyes are obtained. These results may be useful in the incision planning of cataract surgery.
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