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Yu-Chi Liu, Pesus Chou, Pei-Yu Lin, Shih-Jen Chen, Jorn-Hon Liu, Catherine J. Liu, Wen-Ming Hsu, Ching-Yu Cheng; Power Vector Analysis of Refractive, Corneal and Lenticular Astigmatism in an Elderly Chinese Population: The Shihpai Eye Study. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2514. doi: https://doi.org/.
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To investigate the age-related trends in refractive, corneal and lentiuclar astigmatism and to assess the association between lenticular astigmatism and the severity of lens opacity, using vector methods in an elderly Chinese population in Taiwan.
The Shihpai Eye Study was conducted among 1,360 inhabitants aged ≥65 years in Taipei, Taiwan, who undertook a detailed ocular examination, including measurements of refraction and corneal dioptric power using an autokeratorefractometer, and slit lamp biomicroscopy with lens grading using the modified Lens Opacity Classification System III. Of them, 810 participants were eligible for power vector analysis with the primary astigmatism (J0) and oblique astigmatism (J45) components. Lentiuclar astigmatism was derived as refractive minus corneal power values.
The crude prevalence rate of refractive astigmatism (defined ≤-0.75 diopters) was 73.0%. The vector value in both refractive J0 and corneal J0 tends to be more negative with increasing age (both P <0.001), indicating more "against-the-rule" (ATR) astigmatism. Corneal J0 alone accounted for 58% of variability in refractive J0. Both refractive J45 and corneal J45 also increased with age (P <0.001), with more prominent in refractive J45. There were no age trends in lenticular J0 and J45. Nuclear opacity was associated with lenticular J0 (P =0.006) and J45 (P =0.001). For one grade higher in nuclear opacity, lenticular J0 changed toward ATR by 0.04D, and lenticular J45 decreased by 0.05 D.
Astigmatism affects three quarters of elderly Chinese population in Taiwan. With increasing age, the rates of astigmatism increases and refractive and corneal primary astigmatism shifts towards ATR, but lenticular astigmatism remains constant. Continuous corneal changes may be responsible for the age trends in refractive primary astigmatism. Nuclear lens opacity plays a major role in the change of lenticular astigmatism.
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