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T. Leung, A.-C. Lam, C.-S. Kee; Characteristics of Astigmatism as a Function of Age in a Hong Kong Chinese Clinical Population. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1709.
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Astigmatism is a very common refractive error constantly affecting unaided vision regardless of changing in viewing distance or accommodation. While a few studies have reported the prevalence of astigmatism in Hong Kong Chinese populations, they were either small in scale or focused only on a limited age cohorts. This study aims to characterize astigmatism as a function of age in a Hong Kong Chinese clinical population.
All clinical records during 2007 at the Optometry Clinic of The Hong Kong Polytechnic University were used. Only subjects with aided visual acuity better than 6/9 in both eyes and completed subjective refraction were analyzed. The data was subdivided into seven cohorts by age (i.e., ≤10 yrs, 11-20yrs, …, >60yrs). For statistical analyses, refractive errors were decomposed into spherical-equivalent refractive error (SE), J0 and J45 astigmatic components using Fourier analyses. Internal astigmatism was calculated by subtracting corneal astigmatism from refractive astigmatism.
Of the 1474 cases that fulfilled our selection criteria, 60.5% and 28.0% had myopia (SE≤-0.75D) and refractive astigmatism (Cyl≥1.00D), respectively. The prevalence of myopia increased from 22.1% in children (≤10 yrs) to 78.3% in young adults (21-30 yrs), and dipped to 32.8% in the elderly (>60 yrs). Likewise, the prevalence of astigmatism increased from 20.8% in children to 36.8% in young adults but remained high in elderly (38.4%). Among the astigmats, 92.1% of children had WTR but 83.8% of the elderly had ATR astigmatism. As a group, refractive astigmatism was more strongly correlated with corneal (Cyl: r2=0.42; J0: r2=0.62; J45: r2=0.31; all ps<0.001) than with internal astigmatism (Cyl: r2=0.20; J0: r2=0.14; J45: r2=0.17; all ps<0.001). More importantly, unlike the J0 component of internal astigmatism, which was fairly stable across the age groups, the J0 components of both corneal and refractive astigmatism reduced with age.
In this Hong Kong Chinese clinical population, the changes in astigmatism as a function of age were mainly corneal in nature. Further studies are needed to characterize the corneal biometric properties in relation to the genesis of astigmatism with age.
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