Sudden changes in vision can be a sign of a serious eye or brain problem and often need urgent care to save sight or prevent lasting damage. Seek emergency assessment for sudden loss of vision in one or both eyes, a curtain or shadow spreading across your field of view, a sudden burst of new floaters or flashing lights (which can mean a retinal detachment), or sudden double vision.
Severe eye pain with redness, a fixed cloudy pupil, headache, nausea, and seeing halos around lights can indicate acute glaucoma, a sight-threatening emergency. Vision changes accompanied by stroke signs, such as facial droop, weakness, slurred speech, or a severe headache, should be treated as a possible stroke, call your local emergency number.
Gradual blurring, mild dryness, or a slowly changing prescription can be addressed through a routine optician or doctor visit. But any sudden, painful, or one-sided vision change, or vision loss with neurological symptoms, needs same-day emergency care.