Vision changes may indicate a serious problem with the tissue that lines the back of the eyeball (retina), optic nerve, or blood vessels in the eye camera.gif. Evaluation by a health professional is needed right away for sudden vision changes, such as:

Flashes of light (photopsia). Photopsia is brief but recurrent streaks, sparks, or flickers of light, particularly when you move your eyes or head. The flashes of light may be easier to see when you look toward a dark background. -- The brief flashes may occur with retinal detachment.
-- New floaters-shadows or dark objects that float across your visual field. Sudden development of floaters may be a sign of a retinal tear.
-- A dark curtain or veil across part of your visual field. This may occur with retinal detachment.
-- Partial or complete vision loss in one or both eyes. This may occur with retinal detachment.
-- Pain in the eye. Things like sunburn, injury, or infection may cause pain in the eye.
-- Painful sensitivity to light (photophobia). This may be a sign of a problem such as glaucoma or iritis.