A pterygium (silent p, singular) is an invasive patch of tissue on white of the eye that grows onto the clear cornea and looks like the photo below.
Generally, pterygia (plural) begin on the nasal aspect of the eye and grow toward the pupil. Occasionally, they grow from the temporal or outer side of the eye toward the pupil. Just as any tissue needs blood to grow, a pterygium reddens when irritated and growing.
Pterygia are irritated by dryness and sun exposure and should be managed with frequent use of artificial tears and sunglasses. A recent study by Kwok and others revealed that sunlight from the side and behind actually focuses on the nasal area even when wearing sunglasses. Good sunglasses should incorporate antireflective coatings on the back surface of the lenses with as much wrapping protection as possible. Management of pterygia may also include topical medications to control inflammation and redness.
As pterygia grow, they distort the surface of the eye and can change vision. Before a pterygium encroaches on the pupil area it should be surgically removed so that vision can be restored with minimal scarring. If a pterygium is too large, even its surgical removal can result in permanently blurred vision.
If you have a pterygium, have it checked regularly and take take the proper steps to protect your eyes from dryness and sun exposure. Remember, if it's red, it's growing.