Sudden vision loss is a rapid, unexpected decrease in the ability to see, typically occurring over minutes or hours. This abrupt change is a medical emergency because the visual system, which includes the eye, optic nerve, and brain, relies on continuous function. When any part of this complex pathway fails, the delicate light-sensing structures and nerve tissues can quickly suffer irreversible damage. Understanding the mechanism behind the loss is the first step in seeking time-sensitive medical intervention to preserve vision.
Vision Loss Due to Interrupted Blood Flow
The most urgent causes of sudden vision loss involve a lack of blood supply, known as ischemia. The retina, a layer of tissue at the back of the eye, requires a constant supply of oxygenated blood to function. Blockage of the main artery supplying the retina causes Central Retinal Artery Occlusion (CRAO), commonly referred to as an “eye stroke.”
CRAO is an immediate emergency where a clot or cholesterol plaque, often originating from the carotid arteries or the heart, lodges in the central retinal artery. This blockage starves the inner retina of oxygen, causing rapid, profound, and typically painless vision loss. If not treated within a few hours, the loss is often permanent. Because the underlying cause is often systemic, CRAO is considered a stroke equivalent, signaling a high risk for a future brain stroke.
A related event is Central Retinal Vein Occlusion (CRVO), where the main vein draining blood from the retina becomes blocked. This venous blockage causes blood to back up, leading to hemorrhage and swelling within the retina. This often results in blurred or hazy vision that can be sudden or develop gradually. Patients may also experience Amaurosis Fugax, a transient loss of vision described as a curtain momentarily dropping over the eye, which warns of impending vascular occlusion or stroke.
Vision Loss Due to Physical Eye Damage
Some forms of sudden vision loss are caused by mechanical failure or structural changes within the eye. Retinal Detachment is a physically disruptive event where the neurosensory retina separates from the underlying retinal pigment epithelium (RPE). This separation is often caused by fluid leaking through a small tear, commonly due to age-related shrinking of the vitreous gel pulling on the retinal tissue. Once detached, the photoreceptor cells are cut off from the RPE’s metabolic and vascular support, leading to rapid vision loss in the corresponding visual field.
Vitreous Hemorrhage occurs when blood leaks into the vitreous humor, the clear, jelly-like substance that fills the eye’s main cavity. This bleeding can be caused by abnormal, fragile blood vessels associated with conditions like advanced diabetic retinopathy, or by a sudden tear in a normal retinal vessel. The presence of blood obstructs the passage of light to the retina, clouding the visual pathway and causing a sudden decrease in vision.
Acute Angle-Closure Glaucoma (AACG) is a severe mechanical emergency resulting from a sudden spike in pressure inside the eye. This occurs when the iris physically blocks the eye’s primary drainage system, the trabecular meshwork. The inability of the aqueous humor fluid to drain causes intraocular pressure to rise rapidly. This pressure can quickly damage the optic nerve and cause vision loss, often accompanied by intense eye pain, redness, and headache.
Vision Loss Due to Inflammation and Nerve Issues
Disruption of the optic nerve, which transmits visual signals to the brain, is a primary category of sudden vision loss. Optic Neuritis involves inflammation of this nerve, often associated with systemic conditions like multiple sclerosis or viral infections. The inflammation damages the myelin sheath, the protective coating surrounding the nerve fibers, impairing the speed and efficiency of signal transmission. This disruption results in sudden vision loss, typically accompanied by pain when moving the eye.
A dangerous inflammatory cause is Giant Cell Arteritis (GCA), also known as temporal arteritis, which is a systemic inflammation of medium- and large-sized arteries. GCA can affect the ophthalmic artery, reducing blood flow to the optic nerve head and causing ischemic optic neuropathy. This condition requires urgency because the inflammation can progress to involve the artery of the other eye within days, causing permanent and bilateral vision loss. GCA is most common in individuals over 50 and may be preceded by symptoms such as a new headache, scalp tenderness, or jaw pain while chewing.
What to Do Immediately
Sudden vision loss, whether painful or painless, must be treated as an immediate medical emergency. The first step is to call for emergency medical services or go to the nearest emergency room immediately; time is the most significant factor in preserving sight. Patients should not attempt to drive themselves to the hospital.
When reporting symptoms, note exactly when the vision loss began and whether it affects one eye or both, as this information guides diagnosis. Emergency evaluation focuses on quickly determining the underlying cause, often involving an eye examination, blood tests (such as those for GCA inflammation markers), and imaging for vascular blockages or signs of stroke. Rapid treatment, such as high-dose steroids for GCA or procedures to address arterial occlusion, is often the only way to prevent permanent damage to the visual pathway.