The prevalence and risk factors for pterygium in an adult Chinese population in Singapore: the Tanjong Pagar survey

doi:10.1016/S0002-9394(00)00703-0

American Journal of Ophthalmology

Volume 131, Issue 2, February 2001, Pages 176-183

https://doi.org/10.1016/S0002-9394(00)00703-0 Get rights and content

Abstract

PURPOSE: To determine the prevalence and risk factors for pterygium in the Chinese population of Singapore.

METHODS: A population-based survey was conducted in Singapore, an island located 1 degree north of the equator with a stable tropical climate. A disproportionate, stratified, clustered, random sampling procedure was used to select the names of 2000 Chinese people aged 40 to 79 years from the 1996 electoral register in the Tanjong Pagar district of Singapore. Selected subjects underwent a comprehensive interview and ocular examination. Pterygium was diagnosed and graded clinically as grade 1 (transparent), 2 (intermediate), and 3 (opaque). Risks factors associated with pterygium and grade 3 pterygium were evaluated with logistic regression models.

RESULTS: From a total of 1717 eligible subjects, 1232 (71.8%) were examined. There were 120 people with either unilateral (n = 70) or bilateral (n = 50) pterygium, equivalent to an overall prevalence of 6.9% (95% confidence interval [CI], 5.2, 8.8) in the Chinese population aged 40 and older. The prevalence increased linearly with age (chi-square test of trend P < .001) and was higher among men than women (age-adjusted odds ratio [OR], 4.2; 95% CI, 2.5, 6.9). Men aged 70 and above had the highest overall prevalence of 25.4% (95% CI, 18.2, 19.4), but pterygium was not seen in women aged 40 to –49 years. In multivariate analysis, ptergyium was independently associated with increasing age (OR, 7.8; 95% CI, 3.2, 18.8 for persons 70 to 81 years, compared with 40 to 49 years), male sex (OR, 5.1; 95% CI, 2.9, 9.3) and certain occupations; factory workers, production workers and machine operators (OR, 3.1; 95% CI, 1.5, 6.3), as well as laborers and agricultural workers (OR, 3.3; 95% CI, 1.6, 7.0) had higher risks, compared with professionals and office workers. Grade 3 pterygium (n = 36) was also independently associated with male sex (OR, 11.6; 95% CI, 3.5, 38.6) and similar occupations but was not related to age.

CONCLUSIONS: The prevalence of pterygium in Singapore is 7% among Chinese aged 40 years and older. Independent associations with increasing age, male sex, and occupations linked to outdoor work and other exposures suggest a multifactorial cause of this condition.

Section snippets

Methods

Singapore is a city-state located at the tip of the Malaysian peninsula in South East Asia. The country has a constant tropical climate with a monthly mean temperature of 27.4 degrees Celsius, daily mean sunshine of 5.6 hours, and daily mean total global radiation of 463.3 mW/cm² (Meterological Service, Ministry of Environment, Singapore). This investigation was part of a population-based, cross-sectional study of ocular disorders among Chinese people living in the Tanjong Pagar district of

Results

Among the 2000 names initially selected, 46 had died and 235 had moved to addresses outside Tanjong Pagar district before or during the study period. Two persons were considered unfit for examination, leaving 1717 subjects who were eligible to participate in this study. Of this number 1072 were examined in a clinic setting, and an additional 160 subjects were examined at home, with 18 subsequently examined in the clinic as well. The total number of subjects examined in this study was 1232, and

Discussion

We found that 7% of ethnic Chinese older than 40 years in Singapore had pterygium in either eye, with 3% having pterygium in both eyes. There are few population-based studies to compare our rates.4 In the Solomon Islands (located 6 degrees south of the equator), the prevalence was 0.3%.7 On the other hand, in the Blue Mountains Eye Study, a similar overall prevalence of 7.3% was observed in white people aged 49 years and above in a suburb of Sydney, Australia (located 33 degrees south of the

Acknowledgements

We would like to thank David Machin, MSc, PhD, and Tze-Pin Ng, MFPHM, MD, for their statistical help and advice. We would also like to thank Judy Hall, COT, for training technical staff and providing quality assurance services and Rachel Ng, Bernie Poh, and the Clinical Audit department, Singapore National Eye Centre, for their data collection and analysis.

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Human papilloma virus presence and its physical status in primary pterygium
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Pterygium is one of the most frequent pathologies in ophthalmology, and is a benign, overgrowth of fibrovascular tissue, often with a wing-like appearance, from the conjunctiva over the cornea. It is composed of an epithelium and highly vascular, sub-epithelial, loose connective tissue. There is much debate surround the pathogenesis of pterygium and a number of theories have been put forward including genetic instability, cellular proliferation, inflammatory influence, and degeneration of connective tissue, angiogenesis, aberrant apoptosis and viral infection. At present, the involvement of human papillomavirus (HPV) in the genesis of pterygium is controversial, as have reported that HPV is present in 58% of cases, while others have failed to detect HPV in pterygium. In this study, we evaluated the presence and viral genotype of HPV DNA in pterygia and healthy conjunctiva sample, and virus integration into the cellular genome.
Forty primary pterygia samples and 12 healthy conjunctiva samples were analyzed to HPV DNA presence by polymerase chain reaction, using MY09/MY11 primers of HPV-L1 gene. Viral genotype was identified by DNA sequence analysis of this amplicon. HPV integration into the cellular genome was analyzed by western blot detecting HPV-L1 capsid protein.
Presence of HPV was observed in 19 of the 40 pterygia samples. In contrast, healthy conjunctiva samples were negative. To determine virus type, sequence analyses were performed. Interestingly, 11 out of the 19-pterygium samples were identified as HPV-11 type, meanwhile, the remaining 8 pterygium samples were identified as HPV-18. HPV-L1 capsid protein were found only in 3 out of the 10 samples studied.
In conclusion, our study identified the presence of HPV DNA exclusively in pterygium samples and described HPV-11 and -18 genotypes. Our results suggest that HPV may be involved in the pathogenesis of pterygium. On the other hand, the expression of the L1-HPV protein suggests viral integration into the cellular genome.
Pterygium Prevalence and Its Associations in a Russian Population: The Ural Eye and Medical Study
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To assess the prevalence of pterygia and its associations in a population in Russia.
Population-based cross-sectional study.
The Ural Eye and Medical Study was performed in a rural and urban area in Ufa/Bashkortostan 1300 km east of Moscow. Out of 7328 eligible individuals aged 40+ years, 5899 (80.5%) individuals participated and underwent an ocular and systemic examination. Pterygia, defined as conjunctival extensions onto the clear cornea, were diagnosed upon slit-lamp examination and on corneal photographs.
Mean pterygium prevalence (per individual) was 138/5888 (2.3%; 95% confidence intervals [CI]:2.0, 2.7), with bilateral occurrence in 45 individuals (32.6% of patients with pterygium; 0.8% of study population). Pterygium prevalence increased from 0.8% (95% CI: 0.02, 1.6) in the age group from 40 to <45 years to 3.6% (95% CI: 2.1, 5.1) in the age group of 75+ years. In multivariable analysis, higher pterygium prevalence was associated with older age (P = .006; odds ratio [OR]: 1.03; 95% CI: 1.01, 1.04), rural vs urban region of habitation (P < .001; OR: 2.33; 95% CI: 1.57, 3.46), and lower level of education (P = .03; OR: 0.89; 95% CI: 0.81, 0.99), while the pterygium prevalence was statistically independent of sex (P = .34), Russian vs non-Russian ethnicity (P = .59), presence of diabetes mellitus (P = 1.00), arterial hypertension (P = .86), vegetarian vs mixed diet (P = 1.00), blood lipid concentration (P > .30), history of cardiovascular disease (P = .49), or axial length (P = .52).
In this rural and urban, typically multiethnic Russian study population aged 40+ years, a higher pterygium prevalence (mean: 2.3%) was correlated with older age, rural region of habitation, and lower educational level, while it was statistically independent of most other systemic or ocular parameters. A pterygium was not a biomarker for an internal medical disease.
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The present study was conducted to determine the global prevalence and risk factors for pterygium. Three thousand two hundred fifty-five articles were identified, of which 68 articles with a total of 415,911 participants from 24 countries were included in the final analysis. The prevalence of pterygium in the total population was 12% (95% confidence interval [CI] 11–14%). The lowest and highest prevalence rates were, respectively, 3% (95% CI 0.0–9%) in the 10- to 20-year-age group and 19.5% (95% CI 14.3–24.8%) in those over 80 years. The prevalence was 13% (95% CI 11–15%) in men and 12% (95% CI 9–13%) in women. The odds ratio for men was 1.30 (95% CI 1.14–1.45). The lowest prevalence of pterygium was reported in a clinic-based study in Saudi Arabia (0.07%) and the highest prevalence was in China (53%). The odds were 1.24 (95% CI 1.11–1.36) for sunlight exposure over 5 hours, 0.84 (95% CI 0.74–0.94) for smoking, 1.45 (95% CI 1.33–1.57) for living in rural areas, 1.17 (95% CI 1.03–1.32) for alcohol consumption, 1.46 (95% CI 1.36–1.55) for outdoor occupations, and 0.47 (95% CI 0.19–0.57) for use of sunglasses. This is the second meta-analysis arriving at an estimate of 12% for the prevalence of pterygium. According to our results, pterygium risk factors fall in 3 categories: demographic, environmental, and lifestyle factors. Older age, male gender, outdoors occupation, and living in rural environments are the leading demographic risk factors for the development of pterygium. Exposure to sunlight is the most common environmental risk factor, and the results of this study provide a more exact and reliable value of the effect of sunlight exposure. The use of sunglasses and cigarette smoking are protective factors, and the significant effect of alcohol consumption is related to lifestyle factors.
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^☆: The National Medical Research Council, Singapore, funded this work through a grant to the Singapore Eye Research Institute. The British Council for the Prevention of Blindness, London, England, provided additional financial support.

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The prevalence and risk factors for pterygium in an adult Chinese population in Singapore: the Tanjong Pagar survey☆

Abstract

Section snippets

Methods

Results

Discussion

Acknowledgements

Surv Ophthalmol

Am J Ophthalmol

Am J Ophthalmol

Ophthalmology

Am J Ophthalmol

Am J Ophthalmol

Am J Ophthalmol

Ophthalmology

Pterygium—an ophthalmic enigma

Br J Ophthalmol

Aetiology of climatic droplet keratopathy and pterygium

Br J Ophthalmol

Pterygiumprevalence, demography and risk factors

Ophthalmic Epidemiol

Prevalence of pinguecula in Greenland and in Copenhagen, and its relation to pterygium and spheroid degeneration

Acta Ophthalmol (Copenh)

Spheroidal degeneration, keratopathy, pinguecula, and pterygiumin Japan (Kyoto)

Acta Ophthal Scand

Pterygium and ultraviolet radiationa positive correlation

Br J Ophthalmol

Prevalence of pterygium and pingueculathe Blue Mountains Eye Study

Aust N Z J Ophthalmol

Pterygium throughout the world

Pterygium among veterans

Arch Ophthalmol

A pterygium map

Acta Ophthalmol (Copen)

Pterygium. A geographical study

Arch Ophthalmol

Pterygium as an early indicator of ultraviolet insolationa hypothesis

Br J Ophthalmol