Pterygium is a common eye condition characterized by a non-cancerous growth on the white part of the eye. This fleshy, often triangular, tissue can extend from the conjunctiva onto the cornea. While generally benign, it is prevalent globally, affecting an estimated 10-12% of the population.
Understanding Pterygium
A pterygium appears as a raised, fleshy, and often pinkish or reddish growth on the eye’s surface, frequently exhibiting visible blood vessels. It most commonly originates from the inner corner of the eye, near the nose, but can also appear on the outer side. If it grows large enough, it can extend across the cornea, potentially affecting vision by distorting its shape or obstructing the pupil. This differs from a pinguecula, a yellowish, raised bump on the conjunctiva that does not grow onto the cornea and does not impact vision.
Environmental Triggers
Prolonged exposure to ultraviolet (UV) radiation, particularly UVB rays, is a primary environmental factor linked to pterygium formation. This chronic sun exposure can damage the delicate tissues of the conjunctiva, the clear membrane covering the white part of the eye. Beyond UV light, continuous irritation from environmental elements like wind, dust, and sand also contributes to its development. These airborne particles and dry conditions can further irritate the eye’s surface, leading to inflammation and increased susceptibility.
Predisposing Elements
Certain factors increase an individual’s likelihood of developing pterygium. Geographic location plays a role, with higher incidence rates observed in regions closer to the equator (between 30° north and south latitudes) due to more intense UV exposure. Occupations involving significant outdoor time, such as farming, fishing, or construction work, are also associated with increased risk.
Pterygium is more commonly diagnosed in older adults, reflecting cumulative environmental exposure. A genetic predisposition can exist, as familial occurrences suggest heredity may influence the conjunctiva’s response to environmental stimuli. Chronic dry eye is another contributing factor, as persistent irritation can heighten susceptibility.
How Pterygium Develops
Pterygium development begins with chronic exposure to UV light and environmental irritants, which damage the eye’s surface. This damage particularly affects the limbal stem cells, crucial for maintaining the barrier between the cornea and conjunctiva. The breakdown of this protective limbal barrier triggers an abnormal healing response, leading to elastotic degeneration of collagen and elastic fibers within the conjunctiva.
This degeneration results in an uncontrolled proliferation of fibrovascular tissue, an abnormal growth of fibrous tissue and blood vessels. This process involves inflammation and oxidative stress, which further drive tissue remodeling. The expanding conjunctival tissue then invades the clear cornea, forming the characteristic triangular growth.