Common causes for sudden blurry vision include retinal detachment and retinal vein occlusion. According to MedicineNet.com, sudden blurred vision may be sometimes caused by conditions not related to the eyes, such as a stroke or a migraine.
A detached retina is a medical emergency that has several symptoms, including sudden blurred vision, sudden blindness, and flashes or floaters. Retinal detachment may be caused by a retinal tear. Retinal vein occlusion happens due to a blockage of the blood vessels feeding the retina. Common conditions such as astigmatism and short sightedness may cause blurry vision as well but, in most cases, the blurriness is not sudden.