A sudden blind spot in vision, medically termed a scotoma, is an area of reduced or lost sight within the visual field. The onset of a scotoma is a potentially serious medical symptom that requires immediate attention. While some causes are temporary, others signal a sight-threatening or life-threatening event. Determining the exact cause quickly is paramount, as prompt medical attention can often prevent permanent vision loss or address a systemic health crisis.
Temporary and Neurological Causes
Sudden blind spots often originate in the brain, particularly in cases related to temporary neurological phenomena. The most common transient cause is a migraine aura, which manifests as a scintillating scotoma. This visual disturbance appears as a flickering or shimmering spot that gradually expands into a crescent shape with jagged, zigzag lines. These symptoms generally affect both eyes, last between 5 and 60 minutes, and resolve completely, sometimes preceding a headache.
A less common distinction is the retinal or ocular migraine, which causes temporary vision loss or a blind spot in only one eye. This monocular disturbance is caused by a temporary reduction in blood flow or a spasm in the retinal blood vessels. While migraine-related blind spots are usually temporary, their symptoms can mimic more serious conditions.
A Transient Ischemic Attack (TIA), sometimes called a “mini-stroke,” is a serious non-migraine cause. A TIA can cause temporary loss of vision in one eye, known as amaurosis fugax, often described as a curtain coming down over the vision. This is a warning sign of an impending stroke and requires emergency evaluation for underlying vascular disease.
Causes Related to the Retina and Blood Flow
Conditions affecting the retina and its blood supply are urgent causes of sudden blind spots. Retinal detachment occurs when the light-sensitive tissue pulls away from the underlying blood vessels that provide nourishment. This separation is painless, but symptoms include the sudden appearance of flashes of light, an increase in floaters, and a shadow or curtain moving across the field of vision. Immediate intervention is necessary to reattach the retina and prevent permanent blindness.
Blockages in the retinal blood vessels are often described as an “eye stroke.” A Retinal Artery Occlusion (RAO) is a blockage of the main artery supplying the retina, causing sudden, profound, and painless vision loss due to lack of oxygen. This necessitates emergency treatment to restore blood flow.
A Retinal Vein Occlusion (RVO) is a blockage in the vein draining the retina, leading to blood backup, fluid leakage, and swelling. RVO typically results in blurred vision or blind spots that are less abrupt than an RAO, but still require prompt treatment to manage swelling.
Bleeding within the eye’s vitreous cavity is known as a Vitreous Hemorrhage. The vitreous humor is the clear, gel-like substance filling the eyeball. When blood leaks into this gel, it blocks light from reaching the retina, causing clouding, floaters, or a sudden, painless loss of vision. Common causes include diabetic retinopathy, eye trauma, or a retinal tear. These retinal emergencies require rapid diagnosis and time-sensitive treatment to preserve vision recovery.
Optic Nerve and Inflammatory Conditions
The optic nerve transmits visual signals from the eye to the brain and is susceptible to inflammation and damage from reduced blood flow. Optic Neuritis involves inflammation of the optic nerve, often causing pain that worsens with eye movement and a sudden blind spot in the central field of vision. This condition is associated with autoimmune diseases, such as multiple sclerosis, where the immune system targets the nerve’s myelin sheath.
Ischemic Optic Neuropathy (ION) occurs when blood flow to the optic nerve is reduced or blocked. This oxygen deprivation causes the nerve tissue to fail, resulting in sudden, painless vision loss. The non-arteritic form of ION is linked to conditions like high blood pressure and diabetes.
The arteritic form of ION is caused by Giant Cell Arteritis (GCA), a systemic inflammation of the arteries. GCA requires immediate high-dose steroid treatment to prevent permanent, bilateral vision loss.
Emergency Action and Diagnosis
Any sudden change in vision, including a new blind spot, must be treated as a medical emergency. Time is a factor, as conditions like retinal artery occlusion and retinal detachment can cause irreversible damage within hours. Patients should seek immediate care at an emergency room or from an ophthalmologist.
The diagnostic process begins with a detailed visual acuity and dilated eye examination to inspect the retina and optic nerve. Doctors use specialized tools to aid diagnosis. Optical Coherence Tomography (OCT) views retinal layers for swelling or fluid, and angiography assesses blood flow.
Visual field testing maps the size and location of the scotoma, pointing toward the specific area of damage (retina, optic nerve, or visual cortex). For vascular or neurological concerns, imaging such as MRI or CT scans may be performed to look for signs of stroke or inflammation. Treatment depends on the underlying cause, ranging from immediate surgery for a detached retina to managing systemic risk factors for vascular occlusions.