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Vinod Maseedupally, Kerry Ho, Kevin Tran, Helen A Swarbrick; The association between central and peripheral corneal astigmatism based on Fourier analysis in normal eyes. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3542.
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© ARVO (1962-2015); The Authors (2016-present)
With the increasing popularity of large diameter rigid lenses such as orthokeratology lenses, characterizing peripheral corneal shape in relation to the central cornea has become very important. We investigated the association between central and peripheral corneal astigmatism using Fourier analysis.
Three composite corneal topography maps were obtained from 55 healthy participants (26M, 31F; 21±2 years) using the Medmont E300 corneal topographer (V 7.12, Melbourne, Australia). To generate composite maps, topography was captured in the primary, nasal, temporal, inferior and superior gazes. The topographer’s inbuilt software then combined these maps into one single composite map. Right eye axial power maps from the topographer were imported into a custom written MATLAB program (V 8.5 Mathworks Inc., USA). Fast Fourier Transformation was applied to the axial power data to decompose astigmatism into regular and irregular components in the central (2.5 to 4 mm diameter) and peripheral (9 to 10 mm diameter) annular zones. The root mean square (RMS) for regular, irregular and total astigmatism was determined. Based on normality, the Wilcoxon signed rank test and Spearman rank correlations were used to investigate differences and associations between the two regions.
The mean Sim K astigmatism was 1.19±0.83D. The mean RMS for central regular, irregular and total astigmatism was 0.37±0.26D, 0.07±0.04D and 0.13±0.08D respectively. The mean RMS for peripheral regular, irregular and total astigmatism was 0.70±0.43D, 0.46±0.25D and 0.52±0.27D respectively; these were all significantly greater than in the central region (all p<0.001). There was a strong correlation between SimK and RMS central total astigmatism (r=0.89, p<0.001). A strong correlation was also noted between RMS central irregular and central total astigmatism (r=0.67, p<0.001), and between RMS peripheral irregular and peripheral total astigmatism (r=0.96, p<0.001).
Corneal astigmatism is significantly greater in the peripheral than central region. Eyes with higher amounts of astigmatism tend to have higher amounts of irregular astigmatism in the central and peripheral regions. The influence of these differences in corneal shape in central and peripheral regions on large diameter contact lens fitting is yet to be investigated.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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