【摘要】 翼状胬肉为常见的一种眼表疾病，其病因及病理遗传学机制不明。国内外文献关于翼状胬肉的流行病学研究显示患病率由0.3% 到37.46%不等。翼状胬肉发病与地理位置、阳光及紫外线的照射、年龄、性别及经济条件、干眼症等相关。本文就翼状胬肉的流行病学研究现状做一综述，重点在其患病率与危险因素的调查研究方面。
【关键词】 翼状胬肉 流行病学研究 险因素
INTRODUCTION
Pterygium is a common disorder of ocular surface in many parts of the world, affecting one eye or both eyes, described as an “ophthalmic enigma”[1,2]. The exact etiology and pathogenesis of pterygium remains unclear. It is a fibrovascular growth of the conjunctiva, commonly encroaching onto the cornea. It is usually triangular or wing shaped. It not only affects beautiful outlook of the patient, but also affects refractive astigmatism, and is a potentially blinding disease in the advanced stage due to invasion of the visual axis, which can have a significant impact on vision, and may require surgery for visual rehabilitation[3] . The purpose of this review is to present a summary of the more recent literature about the epidemiological study of pterygium.
PREVALENCE
Previouslyreported prevalence rates of pterygium vary widely with geography, race, age, and gender. The epidemiological studies around the world have shown that the prevalence rates range from 0.3% to 37.46%[4, 5]. The earliest estimate was from a survey in New South Wales, Australia, which reported 9.6% prevalence [6]. Moran et al[4] in 1984 reported the prevalence of pterygium was only 0.3%. The prevalence of pterygium obtained from a number of populations in urban Caucasians in Victoria, Australia was 1.2%[7]. The 5.2% prevalence of pterygium in people aged 50 and older in Wardha, India has been reported[8]. In the Blue Mountains Eye Study, Panchapakesan et al[9] found 266 subjects had pterygium (or had a history of pterygium surgery); the prevalence was 7.4% for 3564 participants aged 49 years or older. For 838 Chesapeake Bay watermen, 140 had pterygium, a prevalence of 16.7% in those participants aged 30 years or older in Maryland[10]. The prevalence of pterygium among 477 residents on a tropical island in Indonesia was as high as 17.0%[11], and the black population of the Barbados Eye Study was even higher, 23.4% of 2617 participants aged 40 to 84 years[12] . The highest prevalence rate of pterygium, to our knowledge, was in Aravak and Tukano in indigenous population of the Brazilian Amazon rain forest, 36.6%(97/265) in a survey of prevalence of pterygium and cataract study[13], and in the rural area of Doumen county, China, 37.46%[5].
Wong et al[14] reported a prevalence of 6.9% in a sample of 1717 Chinese aged 40 and older in the Tanjong Pagar survey[14]. In the mainland of China, the prevalence rates of pterygium were also widely associated with geography and race. The prevalence in subjects aged 50 years or above in a rural area of southern China was 33.01%[15]. In two counties of Hainan Province, China, a 7.86% prevalence in 7990 participants aged 12 to 88 was reported[16]. For the older participants in Dagang district, Tianjin, the prevalence of pterygium was 9.02% [17], and there was 20.7% of prevalence of pterygium in 8757 fishermen in littoral of Rongcheng, Shandong Province[18]. Lu et al[19] found an overall prevalence of 14.49% (95% confidence interval [CI]: 13.0315.95) in 2229 native Tibetans at high altitude area in China[19]. The prevalence of pterygium in elderly Mongolians at high altitude was 17.9% (95% CI: 16.319.5) [20].
RISK FACTORS OF PTERYGIUM
Geographic Setting Epidemiological studies suggest an association with chronic exposure to sunlight, with an increased geographical prevalence within a periequatorial pterygium belt of latitudes of 37 north and south of the equator[4, 21]. Due to the strong sunlight, the prevalence of pterygium at the area near equator and low latitude is higher than the area of high latitude. In the south of China, the prevalence is high, which is one of the important factors of vision loss, especially at the rural area[22]. In the rural area of Doumen county, Guangdong Province, (northern latitude of 22°2″, east longitude of 113°5″), the prevalence of pterygium was 37.46%[5].
At the definite area of Beijing City (latitude of 40°), the participants aged 40 and above have an prevalence of pterygium of 3.01%, much lower than the prevalence of 7.86% in participants aged 11 and more in Hainan Province [ 16,23]. Cameron M[24] believed that the prevalence of pterygium is 2.0%4.9% at the latitude of 30°40°. Liu et al[25] reported at the northern latitude of 36°, the prevalence was 8.91%[25]. In Tibet was 22.79% among the people aged 4080 years [26],and 13.88% in Daliyaboyi,Xinjiang Uygur Autonomous Region[27].
Sunlight and Ultraviolet Exposure Many ophthalmologists regard pterygium to be a consequence of ultravioletinduced damage with subsequent elastoid degeneration of the subepithelial connective tissue[2831]. Studies have shown that spending longer periods of time outdoors has led to an increased risk of pterygium, with cumulative exposure to ultraviolet (UV) radiation playing a significant role; it is therefore strongly related to ocular sun exposure[32,33]. A casecontrol study of 278 patients working in outside environment was shown to be 4 to 11 times more likely to have pterygium than those working indoors[34]. The UV type B light in solar radiation has been found to be the most significant environmental factor in pterygium pathogenesis[4, 21].
McCarty et al[7] found the lifetime ocular sun exposure was an independent risk factor of pterygium (odds ratio [OR], 1.63) and the attributable risk of sunlight and pterygium was 43.6%. They also found that rural residence is a risk factor for pterygium (OR, 5.28) and made a conclusion that pterygium is a significant public health problem in rural areas, primarily due to ocular sun exposure. At QinghaiTibet Plateau, at the mean altitude of 3450m and 3750m, the prevalence rates of pterygium were 17.9% (95%CI: 16.319.5) and 14.49% (95% CI: 13.0315.95) respectively[19,20] . The unique environment of this high altitude area includes low air pressure, hypoxia, dry and cold weather, long periods or sunshine, strong solar infrared light and ultraviolet radiation, which all have an effect on pterygium. The prevalence of pterygium was high (8.6%) in Eskimo in the south of Greenland. They believed it may be because of the ultraviolet reflection of covered snow[35]. This conclusion was consistent with ZES and HES in China[19, 20]. The ZES found use of sunglasses/crystal spectacles was a protective factor for pterygium (OR, 0.31; 95%CI: 0.120.77) as was the use of a wide brimmed hat (OR, 0.30; 95%CI: 0.200.46). The subjects who seldom used glasses and/or wore a hat had a strong positive correlation with presence of pterygium (OR, 4.6; 95%CI: 1.911.3 and OR, 3.6; 95%CI: 2.45.4 respectively). Lu et al[19] believed the protective mechanism is related to the ability of glasses and a hat to block UVB wavelengths of sunlight or to shield the eye from other harmful environmental exposures, since hazardous environmental factors play a very important role in pterygium formation. The HES found the participants who seldom use sunglasses and/or wear a hat when they are outside had a positive association with pterygium (OR, 1.5; 95%CI: 1.21.9 and OR, 1.3; 95%CI: 1.11.7 respectively). These results were similar to the Barbados Eye Study and Rosenthal et al[9, 36].
The people with pterygium has a much higher prevalence of cataract than the people without pterygium. It has shown cataract and pterygium might have common etiological factor[24],and it was confirmed by the studies of Taylor et al[21] and Lim et al [37]. Taylor et al believed the development of cataract and pterygium is related to the exploration of blue light(400500nm) and visible light (400700nm).
Age Studies that were based on adult population confirm the higher prevalence of pterygium with increasing age. A prevalence study in 5147 residents of Victoria over the age of 40 (range 40 to 101 years) found a weighted rate of pterygium of 2.83%, which tended to increase with age, with 6.4% of those aged 80 to 89 years found to have pterygium[7].
In ZES, pterygium was independently associated with increasing age for persons aged 7079 years, compared with those aged 4049 years (OR, 2.0; 95% CI: 1.42.8)[19]. In HES, the prevalence increased with older age (chisquare test of trend P<0.01). The prevalence of pterygium was 13.5% (95%CI: 11.215.9) in participants aged 40 to 49, but 27.5% (95%CI: 15.239.7) for those aged 80 and above[20].
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