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Title: Characteristics of astigmatism as a function of age in a Hong Kong clinical population
Authors: Leung, TW 
Lam, AKC 
Deng, L
Kee, CS 
Issue Date: Jul-2012
Source: Optometry and vision science, July 2012, v. 89, no. 7, p. 984-992
Abstract: Purpose: To characterize astigmatism as a function of age in a Hong Kong clinical population. Methods: All records from new clinical patients at a university optometry clinic in the year 2007 were used for the study. Only data from subjects with corrected visual acuity ≥6/9 in both eyes and with completed subjective refraction were analyzed. The subjects were divided into seven age groups by decade (i.e., 3 to 10 years, 11 to 20 years, ⋯, >60 years). Refractive errors were decomposed into spherical-equivalent refractive error (M), J0, and J45 astigmatic components for analyses. Internal astigmatism was calculated by subtracting corneal astigmatism from refractive astigmatism (RA). Results: Of the 2759 cases that fulfilled our selection criteria, 58.9% had myopia (M ≥-0.75 D) and 28.4% had RA (Cyl ≥ 1.00 D). The prevalence of RA increased from 17.8% in the 3 to 10 years age group to 38.1% in the 21 to 30 years age group. It then dipped to 25.8% in 41 to 50 years age group but increased again to 41.8% in the >60 years age group. Among the astigmats, almost all 3- to 10-year-old children (92.6%) had with-the-rule (WTR) astigmatism, but a majority of the elderly (>60 years) had against-the-rule (ATR) astigmatism (79.7%). For a subset of subjects who had both subjective refraction and keratometric readings (n = 883), RA was more strongly correlated with corneal (r = 0.35 to 0.74) than with internal astigmatism (r = 0.01 to 0.35). More importantly, the magnitudes of both refractive and corneal J0 were consistent with synchronized decrements (-0.15 and -0.14 D per 10 years, respectively) after the age of 30 years, indicating that the shift toward more ATR astigmatism was related to corneal change. Conclusions: In this Hong Kong Chinese clinical population, the prevalence rates of both myopia and astigmatism increased during the first three decades and shared a similar trend before the age of 50 years. The manifest astigmatism was mainly corneal in nature, bilaterally mirror symmetric in axis, and shifted from predominantly WTR to ATR with age.
Keywords: astigmatism
Hong Kong Chinese
myopia
prevalence
refractive errors
Publisher: Lippincott Williams & Wilkins
Journal: Optometry and vision science 
ISSN: 1040-5488
EISSN: 1538-9235
DOI: 10.1097/OPX.0b013e31825da156
Rights: Copyright © 2012 American Academy of Optometry
This is a non-final version of an article published in final form in Optometry and Vision Science: July 2012 - Volume 89 - Issue 7 - p 984-992. The Optometry and Vision Science’s website is available at https://journals.lww.com/optvissci/pages/default.aspx
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