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Y. Yamashiro, R. Honda, M. Kojima, Y. Sakamoto, Y. Kawakami, J. Qu, K. Sasaki, H. Sasaki; Does Corneal Curvature Radius Contribute to Pathogenesis of Pterygium? - A Report From Chinese Ophtalmic Surveys in Hainan and Shanxi. Invest. Ophthalmol. Vis. Sci. 2008;49(13):6034.
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It was reported that a steeper cornea might focus more incident light at the temporal side of the nasal limbus. To elucidate this assumption, the correlation between corneal curvature radius (CR) and pterygium in Chinese farmers was evaluated.
Subjects comprised 558 participants of an ophthalmic survey in Hainan (March, 2006) and 690 in Shanxi (July, 2006) province in China. All of them lived in rural areas and were aged 50 ≥ yrs. Diagnosis of pterygium where conjunctival tissue encroached onto the cornea, was performed by the same observer in both studies. Subjects with corneal opacity, trauma, past history of pterygium surgery, aphakia and pseudophakia were excluded from the study. CR was measured by Auto Kerato-Refractmeter (KR 8000P, TOPCON). CR of the cases with unilateral pterygium (111 cases, 61.7±10.3 yrs in Hainan, 77 cases, 63.6±8.6 yrs in Shanxi) and without pterygium (149 cases, 57.4±9.6 yrs in Hainan, 558 cases, 60.1±8.8 yrs in Shanxi) was compared. Since the CR changed when pterygium developed, cases with unilateral pterygium were enrolled and CR of same case eyes without pterygium was also measured. In cases without pterygium, CR in right eye were measured. CR was assigned to four groups; A (<7.25mm), B (7.25-7.5 mm), C (7.5-7.75 mm), D (>7.5mm). For the statistical analysis, logistic regression adjusting age and gender was applied.
Prevalence of pterygium was 71.7% in Hainan and 18.8% in Shanxi. The rates of pterygium in A, B, C and D groups were 29.4, 42.6, 48.0, and 33.8 % in Hainan, and 8.2, 12.3, 13.8, 10.6 % in Shanxi. For both provinces, prevalence of pterygium was the lowest in A group and highest in C group. However, no significant difference was observed between A and C. After adjusting for age and gender, there was some tendency of increased risk of pterygium in C group in both areas.
Prevalence of pterygium was not higher in steeper CR cases of Chinese famers. For the cause of risk-elevation-tendency in medium degree corneal curvature radius group, there may be something else which influences ocular UV exposure such as individual behavior, palpebral configuration or kerato-conjunctiva exposed area.
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