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B. Tan, Y.-L. Chen, L. Shi, J. W. L. Lewis, M. Wang, P. Hull; Ametropic Cornea Biometry. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1321.
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To gain the knowledge of population-based statistics of cornea biometry and examine the correlation between ocular refractive error and the cornea shape.
We reviewed recently published research studies that included measurements of both refractive errors and cornea shape factors, viz the radius of vertex curvature (RVC) and/or the asphericity or cornea conic constant (CCC). Using the available data of young adults’, we have established the statistical description of the average corneal RVC and the CCC as functions of refractive error. Using these results, the distributions (standard variation) were determined for a range of different refractive groups. The result of each research study are compared with overall population distribution to determine the statistical variation due to age, gender, and race.Results &
The RVC review was performed using 20 studies: Over the refractive range of -14 to +5 diopter, the average adult RVC for 440 subjects is obtained by linear regression to be: RVC=7.748+0.0155K (mm); where K is the refractive error in diopter, p<0.0001, and r2=0.0432. The results of the RVC were assumed to be normally distributed, and the standard deviation of these data (from the fitted equation) is 0.264 mm. No significant disparity in this deviation from emmetropic was found for the myopic and hyperopic groups. Only one paper describes children’s (9-15 year old) RVC (Garner 1992, Maylay) in both myopic and hyperopic subjects. The RVC result is within the average adult distribution. A study in infants (Cook 2003) also shows that the cornea radius of curvature develops to nearly the adult size from 33 to 53 weeks of age. On the subject of gender difference, many studies show that at the same refraction males exhibit a flatter cornea than females by about 0.1 mm. There is no significant evidence to present the RVC difference in race at any specified refraction.Cornea asphericity review is made from 10 papers. CCC= -0.2654 -0.0145K, n=236 adults, p=0.0029, r2=0.0373, RMS deviation=0.22. Only 1 paper studied CCC in children (Homer 2000, 11-13 year old children). The children tend to have a larger conic value compared to adults, indicating a less flat periphery. Although some studies were performed on gender difference, no significant differentiation is found.
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