Something always causes the eye to go blind. And there is a difference between bad vision, legal blindness and total blindness. Most of the things that cause sudden legal and total blindness occure due to diseases that are common in aging.
A partial list of such problems: central retinal artery occlusion, central retinal vein occlussion, angle closure glaucoma, arteritic anterior ischemic optic neuropathy, severe bilateral eye trauma, hereditary optic nueropathy, retinitis pigmentosa (severe) etc.
The best way to prevent this is an annual examination with an eye physician and surgeon (Ophthalmologist = Eye MD) and eye protection for activities with high chance of eye injury.
JCH MD Eye Physician and Surgeon