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What is Pterygium?

A pterygium (wing) is a triangular-shaped mass of blood vessels and scar tissue that grow onto the cornea’s surface. Pterygia typically start on the nasal aspect of the cornea (near the nose), and they can grow large enough to cover the pupil, leading to severe astigmatism and even blindness. While both eyes are usually involved, unilateral cases are also possible.

Pterygium formation has been proven to be directly linked to long-term exposure to UV light and dust, though genetic factors also appear to be involved. The frequency of the condition varies from 1% to 33% in various regions of the world. It occurs more commonly among males than females and people living closer to the equator. The risk also increases with age.

Preventing pterygia may include wearing sunglasses and a hat in an area with strong sunlight. Among those with the condition, an eye lubricant can help with symptoms. Pterygia never improves, and artificial tears, anti-inflammatory drops, and corticosteroids are ineffective in resolving the condition. As such, there’s no effective treatment available. Some symptoms, such as dry eyes and irritation, can be addressed with artificial tears, but surgery may be considered for unmanageable symptoms and/or for cosmetic reasons.

Patient Burden

The symptoms of pterygium include redness, ocular irritation/inflammation, foreign body sensation, tearing, and dry and itchy eyes. In advanced cases, pterygia can affect vision as they invade the cornea. Pterygia can eventually obscure the optical center of the cornea, leading to astigmatism and corneal scarring.

Many people are bothered by the cosmetic appearance of the eye and the stigma of having red, discolored eyes. As it is associated with excessive sun exposure, wearing protective sunglasses with side shields and/or wide-brimmed hats and using artificial tears throughout the day may help prevent their formation or stop further growth.

Surfers and other water-sport athletes should wear eye protection that blocks 100% of the UV rays from the water, as often used by snow-sport athletes. Many of those at the greatest risk of pterygium due to sun exposure do not understand the importance of protection.

Prevalence of Pterygium

A recent (2018) systemic review and meta-analysis of 3255 articles and 415,911 participants from 24 countries studying the prevalence and risk factors of pterygium formation concluded that the prevalence of pterygium in the total population was 12% (95% confidence interval). The lowest and highest prevalence rates were, respectively, 3% (95% CI) in the 10- to 20-year-age group and 19.5% in those over 80 years. The prevalence was 13% in men and 12% in women.

The odds were 1.24 for sunlight exposure over 5 hours and 1.46 for outdoor occupations. Pterygium risk factors fall into 3 categories: demographic, environmental, and lifestyle factors. Older age, male gender, outdoor occupation, and living in rural environments are the leading demographic risk factors for developing pterygium. Exposure to sunlight was found to be the most common environmental risk factor.

The incidence of pterygium within the United States varies with geographical location. In the continental United States, prevalence rates vary from less than 2% above the 40th parallel to 5-15% in latitudes between 28-36°. Worldwide, Pterygium prevalence is high in the “pterygium belt” between 30 degrees north and 30 degrees south of the equator.

The prevalence of pterygium is reported to be 3% in Australians, 23% in blacks in the United States, 15% in Tibetans in China, 18% in Mongolians in China, 30% in Japanese, and 7% in Singaporean Chinese and Indians. In a population-based study from rural central India, the prevalence of pterygium increased from 6.7±0.8% in the age group from 30–39 years to 25.3±2.1% in the age group of 70–79 years.

Three population-based studies have described the incidence of pterygium. Barbados eye study has described the nine-year incidence of pterygium to be 11.6% (95% CI, 10.1–13.1), the Beijing Eye Study described the 10-year incidence of pterygium in the adult Chinese population to be 4.9%, and the five-year cumulative incidence in Bai Chinese population in a rural community was 6.8% (95% CI, 5.2–8.4).

Depending on the population studies, the prevalence of pterygium lies within the range of 1% to more than 30%. According to a meta-analysis of 20 studies published in 2015, the pooled prevalence of pterygium is around 10%. The maximum prevalence rate for pterygium has been reported in a Chinese study on a rural population, where a rate of 33% was yielded.

In a North American study, the prevalence of pterygium was 2.5-3 times higher in the Black population compared with Whites.

Global Information:

  • The prevalence of pterygium was 10.2% worldwide, with the highest prevalence in low-altitude regions (Liu et al, 2013).
  • Increased incidence of pterygium is noted in the tropics and in an equatorial zone between 30° north and south latitudes (Liu et al, 2013).
  • Higher incidence is associated with chronic sun exposure (ultraviolet light), older age, male sex, and outdoor activity (Liu et al, 2013).

Regional Information:

  • One study among a Latino population in Tucson, Arizona, United States, found the prevalence of pterygium to be 16% (West et al, 2009).
  • A hospital-based study in Lima, Peru, reported the prevalence of pterygium to be 31%, with a significant increase in prevalence with increasing age (Rojas et al, 1986).
  • In a population-based sample in Botucatu City, Sao Paulo State, Brazil, the reported prevalence was 8.12%, affecting primarily 40–50-year-old males (Shiratori et al, 2010).