The white of the eye is covered by a transparent loose skin known as conjunctiva. Just as skin of the hands and feet can become thickened with use over the years, so can the conjunctiva. Thickening of the conjunctiva is more common in hot and dry environments, or in patients with dry eyes.
A pterygium is a flap of thickened conjunctiva on the nasal side of the eye that grows abnormally over the surface or the cornea (clear window of the eye). When a pterygiom is small it causes minor irritation and redness. As it enlarges over the years it can become more irritating and more cosmetically noticeable. Eventually it can grow right across the central cornea and permanently damage the vision. Pterygia are best treated before they get close to the central cornea to prevent long term complications. They require surgical excision with a conjunctival graft to prevent recurrence.
A small pterygium growing over the nasal cornea.
A pingueculum is a thickened area of conjunctiva that can develop on the outside edges of the eye. Unlike a pterygium, which grows over the cornea, a pingueculum remains only on the conjunctiva. It too can cause minor irritation, or become occasionally inflamed, red and gritty. Pinguecula will never damage the vision and can be either left untreated, or treated with simple lubricant eye drops.
An inflamed pingueculum highlighted with a yellow dye.