Sudden vision loss (SLVL) is a rapid decrease in vision occurring over minutes to hours, often affecting only one eye. This symptom signals a serious event along the visual pathway, from the eye to the optic nerve. Because the underlying causes can lead to permanent blindness or indicate a systemic stroke, SLVL is always considered a medical emergency. Immediate attention at an emergency department or by calling 911 is necessary to maximize the chance of preserving sight and diagnosing potentially life-threatening conditions.
Vascular Blockages Affecting the Eye
Interruption of blood flow to the retina, often termed an “eye stroke,” is a major cause of abrupt vision loss. The retina requires a constant supply of oxygenated blood, and any blockage causes rapid tissue death.
Central Retinal Artery Occlusion (CRAO) is the most devastating vascular event, resulting from a clot blocking the main artery supplying the retina. This blockage causes sudden, severe, and usually painless loss of vision in one eye, often dropping to counting fingers or worse within minutes. Since the retina cannot survive without oxygen for long, the window for intervention to salvage vision is very narrow, typically only a few hours.
A Central Retinal Vein Occlusion (CRVO) occurs when the main vein draining blood from the retina becomes blocked. This blockage causes blood and fluid to back up, leading to retinal hemorrhage and swelling (macular edema). Vision loss from CRVO is often less sudden and less profound than CRAO, developing over hours or days, and may present as blurry or distorted vision.
Transient Vision Loss, or Amaurosis Fugax, is temporary vision loss in one eye, often described as a curtain passing over the visual field, which resolves within minutes. This temporary darkening is a transient ischemic attack (TIA) of the eye, caused by a small embolus temporarily blocking the retinal artery. Although vision returns, this symptom is a warning sign of underlying vascular disease, such as carotid artery stenosis, and signals an increased risk of a permanent brain stroke.
Structural Emergencies of the Retina
Structural failure within the eye can cause a sudden collapse of vision, often accompanied by distinct visual phenomena. The retina is a thin, light-sensitive layer that must remain attached to the underlying tissue for nourishment.
Retinal Detachment occurs when the retina peels away from the supportive tissue beneath it, separating it from its blood supply and causing the affected area to cease functioning. This separation often begins with a tear, allowing fluid from the vitreous gel to seep underneath and push the retina away. Early symptoms include a sudden increase in floaters (specks or cobwebs) and flashing lights (photopsias). As the detachment progresses, patients report a dark shadow or curtain moving across their field of vision, signaling severe vision loss.
Vitreous Hemorrhage is bleeding into the vitreous humor, the clear, gel-like substance that fills the main cavity of the eyeball. The presence of blood obstructs the passage of light to the retina, causing a sudden, diffuse clouding of vision, often described as a shower of cobwebs or a heavy mist. Common causes include abnormal blood vessel growth due to advanced diabetic retinopathy, or the tearing of a retinal vessel during a posterior vitreous detachment or eye trauma.
Inflammatory and Nerve-Related Causes
Sudden vision loss can also originate in the optic nerve, the cable that transmits visual information from the retina to the brain. Inflammation or lack of blood flow to this nerve can severely compromise sight.
Optic Neuritis involves inflammation and swelling of the optic nerve, often linked to autoimmune conditions like Multiple Sclerosis (MS). This condition causes vision loss that develops over several days, not instantly, and is frequently accompanied by pain, especially when moving the eye. Patients may also notice a reduction in color vision, where colors appear washed out or dull.
Giant Cell Arteritis (GCA) is a particularly urgent nerve-related cause, involving systemic inflammation of the blood vessels. This inflammation can cut off the blood supply to the optic nerve, resulting in Arteritic Ischemic Optic Neuropathy (AION). Vision loss from GCA is severe, profound, and often permanent, requiring immediate, high-dose steroid treatment to prevent vision loss in the other eye. GCA is frequently preceded by systemic symptoms, such as a new, severe headache, jaw pain when chewing, or tenderness of the scalp.
Acute Pressure Changes in the Eye
A rapid, severe increase in the fluid pressure inside the eye can cause an acute ophthalmic emergency. This high pressure quickly damages the optic nerve, leading to vision loss.
Acute Angle-Closure Glaucoma occurs when the eye’s natural drainage system, located between the iris and the cornea, becomes abruptly blocked. This blockage prevents the aqueous humor fluid from draining, causing intraocular pressure to spike dramatically, often exceeding 40 mm Hg. The resulting pressure on the optic nerve and cornea leads to a painful, sudden vision loss. Accompanying symptoms include severe eye pain, a throbbing headache, nausea, vomiting, and the perception of rainbow-colored halos around lights.
Immediate Steps and What to Expect
Any sudden loss of vision demands immediate medical attention; go to the nearest emergency department or call emergency services without delay. Do not attempt to drive yourself or wait for a routine appointment. The speed of treatment is directly linked to the final visual outcome for many conditions, such as vascular blockages and retinal detachment.
Upon arrival, the emergency team will assess your visual acuity, check pupil responsiveness, and measure intraocular pressure. An ophthalmologist will perform a dilated eye exam to visualize the retina and optic nerve for signs of detachment, hemorrhage, or vascular occlusion. Further tests may include blood work to check for inflammatory markers (like those seen in GCA) or imaging studies such as an ultrasound of the eye or a carotid artery scan.
The prognosis for recovery varies widely. For conditions like CRAO, vision loss is often permanent despite immediate treatment, while a quickly treated retinal detachment or acute glaucoma attack may have a better outcome. The goal of emergency treatment is to prevent further damage and, if possible, to restore blood flow or reattach the retina. Immediate, aggressive care maximizes the chance of preserving eyesight and addresses any underlying systemic causes that could threaten life.