Pterygium is like a skin growing across the cornea. They are slow growing, can be unsightly and occasionally have to be surgically removed if they are growing close to the pupil where they could block vision.
They are caused by sun and dust. They start as a small lump with extra blood vessels on the sclera (the white of the eye). Most people in hot climates develop this to some degree. Eventually over many years they start growing across the cornea (the clear covering over the coloured iris).
Prevention is definitely better than cure and it is simply a matter of wearing sunglasses as much as possible and as early in life as possible to cut out the UV light that triggers them. Even later in life wearing sunglasses can halt the progression of the pterygium.
Our retinal camera can also be used to photograph the pterygium so it can be monitored for growth over the years.