Temporary vision loss, often described as vision “going black” for a few seconds, refers to a brief period where sight diminishes or disappears. This experience can be unsettling. While such episodes are often harmless, they can sometimes signal an underlying health concern. Understanding the potential reasons behind these fleeting visual disturbances can help determine appropriate next steps.
Common Causes of Fleeting Darkness
One frequent cause of momentary vision loss is orthostatic hypotension, often perceived as a “head rush” when standing up quickly. This occurs because gravity pulls blood into the legs, leading to a temporary reduction in blood flow to the brain and eyes as the body adjusts. This delay can result in momentary dimming or blacking out of vision.
Dehydration can also contribute to these episodes by reducing overall blood volume, which lowers blood pressure and diminishes blood reaching the brain. Similarly, a significant drop in blood sugar levels, known as hypoglycemia, can deprive brain cells of their primary energy source, leading to vision loss. This might occur if someone skips meals or engages in strenuous activity without adequate glucose intake.
Hyperventilation, or rapid, shallow breathing, can cause vision to go black by altering blood gas levels. When too much carbon dioxide is exhaled, blood vessels in the brain can constrict, temporarily reducing blood flow and oxygen supply to the visual centers. Straining, such as during a bowel movement, heavy lifting, or even a strong cough, can also temporarily increase pressure in the chest and abdomen. This pressure can impede venous return to the heart, leading to a transient decrease in blood flow to the brain and eyes.
Serious Conditions Linked to Temporary Vision Loss
Temporary vision loss can occasionally point to more serious medical conditions, although these instances are less common. Transient ischemic attacks (TIAs), often referred to as “mini-strokes,” involve a temporary blockage of blood flow to the brain, which can manifest as sudden, fleeting vision loss in one eye. This specific type of vision loss, called amaurosis fugax, typically appears as a curtain descending or rising across the visual field.
Certain types of migraines, particularly ocular migraines, can also cause temporary visual disturbances, including blind spots or zigzag patterns, which may precede or accompany a headache. Cardiac issues, such as arrhythmias or heart valve problems, can impair the heart’s ability to pump blood effectively, leading to insufficient blood flow to the brain and eyes. Conditions like severe anemia, characterized by a low red blood cell count, reduce the blood’s oxygen-carrying capacity, potentially causing a temporary reduction in oxygen supply to the visual pathways.
Narrowing of the carotid arteries in the neck, known as carotid artery stenosis, can restrict blood flow to the brain and eyes. Small pieces of plaque or clots can break off from these narrowed arteries and travel to the retinal artery, causing transient monocular vision loss.
When to Consult a Doctor
Seeking medical advice for temporary vision loss is advisable, particularly if the episodes are recurrent or occur without an obvious benign trigger like standing up quickly. It is important to consult a doctor if the vision loss is accompanied by other symptoms. These might include dizziness, weakness or numbness on one side of the body, speech changes, confusion, or severe headache.
Immediate medical attention is warranted if temporary vision loss occurs following a head injury. If these episodes happen frequently, even without other alarming symptoms, a doctor’s evaluation can help identify any underlying causes. A doctor can determine if the vision loss is benign or indicative of a more significant health issue.
Immediate Steps During an Episode
If you experience your vision going black for a few seconds, the immediate priority is to ensure your safety. Sit or lie down quickly to prevent a fall, especially if you feel lightheaded or unsteady. Remaining calm during the episode is beneficial, as panic can exacerbate symptoms or lead to further discomfort.
Avoid making sudden movements while your vision is impaired, and wait patiently for your sight to return completely before attempting to stand or move around. If you are prone to such episodes, it is recommended to avoid activities like driving or operating heavy machinery. This precaution helps prevent potential accidents until the cause of the temporary vision loss is understood.