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Phillip Jonathan Buckhurst, Catriona Hamer, Hetal Buckhurst, Christine Purslow, Nabil Habib; The relationship between corneal astigmatism and refractive astigmatic error in pseudophkic eyes. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1906.
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© ARVO (1962-2015); The Authors (2016-present)
Following cataract surgery any uncorrected corneal astigmatism translates into ocular refractive astigmatic error (RAE). When implanting a toric intraocular lens (IOL) the power and orientation of the IOL is determined after assessment of corneal power via keratometry or topography. A limitation of both these techniques is that they only evaluate the anterior corneal surface. Schiempflug tomography assesses both the anterior and posterior corneal surface allowing determination of the total corneal astigmatic error. This study examines the relationship between corneal astigmatism and RAE.<br />
The study examined 80 subjects (74.8±9.6 years) who had undergone small incision sutureless cataract surgery with postoperative corneal astigmatism >0.75DC. All subjects were implanted with a monofocal, non-toric, aspheric IOL. Scheimpflug tomography was used to determine the postoperative anterior corneal astigmatism (ACA) as well as the total corneal astigmatism (TCA). An investigator masked to the tomography results conducted subjective refraction to determine RAE. The astigmatic power of the cornea and the overall manifest refraction were assessed following conversion into vector format (J0/J45). The relationship between ACA, TCA and RAE was assessed through repeated measures ANOVA and a stepwise multiple linear regression. <br />
The mean RAE, ACA and TCA were 1.11D (J0: 0.73±1.05; J45: -0.01±0.67), 1.07D (J0 0.12±1.02; J45: 0.01±0.67) and 1.30D (J0: 0.38±1.09; J45: 0.00±0.86), respectively. Along the horizontal power meridian (J0), ACA was found to be significantly lower than RAE (p<0.05). In contrast TCA was found to be similar to RAE along both J0 and J45 (p>0.05). Corneal astigmatism was found to account for only 18% of the variation in RAE; this stepwise regression model found that only TCA and not ACA was a significant predictor of RAE.<br />
When compared to the anterior corneal astigmatism, total corneal astigmatism showed a greater association with the overall refractive corneal astigmatism. These results would suggest that it is important to select the power and position of toric IOL in accordance with total corneal astigmatic power rather than just the anterior corneal astigmatism.<br />
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