Depends. The eye (like a camera) has many parts, blindness can result from disease to any of the parts. Some parts can be replaced such as the cornea (with a cornea transplant) or a cataract with a lens implant, so blindness due to corneal or lens conditions can be reversible. When there is severe damage to the retina or optic nerve causing blindness, reversing becomes more difficult or impossible.
Depends on the cause. Reversible blindness occurs when the nerve and film layer of the eye are normally functioning but the window(s) of the eye (cornea and lens) become clouded. If the nerve or retina are damaged there is less chance of vision recovery. Also, if the blindness has been present since birth and is not reversed until later in life, only a small amount of vision may recover.