Pterygium surgery is performed to remove a pterygium (plural pterygia), a benign (non-cancerous) growth of the conjunctiva, the clear, thin tissue that lies over the sclera, the white part of the eye. It may affect one or both eyes, and can be caused by overexposure to bright sunlight. A pterygium usually appears as a painless area of raised white tissue, which may become inflamed and cause burning and irritation. No treatment is needed unless the pterygium starts to affect vision (by expanding onto the cornea), affects wearing contact lenses or causes symptoms that are hard to control, such as irritation and redness. In these cases it is removed with surgery. The preferred procedure is to remove the pterygium and cover the area with a patch of healthy conjunctiva from beneath the upper eyelid. This is sutured (stitched) into place. The procedure is carried out under local anaesthesia and takes about 30 minutes.