Vision going black when you stand is due to a brief drop in blood pressure (orthostatic hypotension). Stand slowly and drink fluids, and see a doctor if it keeps happening.
Why
Standing makes blood pool in the legs. If pressure falls briefly, less blood reaches the brain, which causes a gray or black vision. This is called orthostatic hypotension.
Causes
- Dehydration.
- Medicines such as diuretics.
- Anemia.
- Standing quickly.
- Heart or nerve conditions.
What helps
Stand slowly, drink water and add salt if told to by a doctor.
See a doctor
If it is frequent, or if you faint.
Orthostatic changes
When you stand, gravity pulls about 500 to 800 milliliters of blood into the legs and abdomen. The body normally compensates within seconds by tightening blood vessels and speeding the heart. If this response is slow, blood pressure briefly drops, and the brain and eyes get less blood, which can cause vision to gray out or go black.
Orthostatic hypotension
This is defined as a drop in systolic blood pressure of at least 20 mm Hg or diastolic of at least 10 mm Hg within 3 minutes of standing. It affects about 5% of adults overall and up to 30% of those over 70.
Causes
- Dehydration and heat.
- Medications: blood pressure drugs, diuretics, antidepressants, alpha blockers, drugs for Parkinson’s disease and erectile dysfunction drugs.
- Alcohol.
- Prolonged bed rest.
- Pregnancy.
- Anemia.
- Heart problems such as arrhythmias, heart valve problems and heart failure.
- Endocrine issues: low cortisol (Addison’s disease), diabetes.
- Neurological conditions such as Parkinson’s disease and autonomic neuropathy.
- Postural orthostatic tachycardia syndrome (POTS), which mostly affects young women.
What helps
- Stand up slowly. Sit on the edge of the bed for a minute first.
- Drink water, aiming for 2 to 3 liters per day if advised by your doctor.
- Add salt only if your doctor approves.
- Wear compression stockings.
- Avoid standing still for long periods.
- Eat smaller meals.
- Cross your legs or tense your muscles when feeling faint.
See a doctor if
It happens often, leads to falls, or comes with chest pain, shortness of breath, palpitations or confusion. Fainting while exercising or with a family history of sudden death needs urgent evaluation.
Mechanism of a gray out
When you stand, gravity pulls about 500 to 800 ml of blood into the legs and abdomen, and blood pressure sensors in the neck and chest trigger the heart to beat faster and vessels to tighten. If this baroreflex is slow, less blood reaches the brain and the eyes, causing tunnel vision, graying or blacking out, and lightheadedness, called presyncope. It usually lasts seconds. Dehydration, heat, alcohol, standing from a hot bath, certain medicines and pregnancy increase the chance.
POTS and prevention
Postural orthostatic tachycardia syndrome (POTS) causes a heart rate rise of at least 30 beats per minute (40 for teens) on standing without a big pressure drop, and affects an estimated 1 to 3 million Americans, mostly women. Rise slowly, drink 2 to 3 liters of fluid a day if your doctor agrees, add salt only on medical advice, use compression stockings and do leg muscle tensing or crossing the legs. See a doctor if you faint, have chest pain, palpitations, or symptoms several times a week. Call 911 for fainting with chest pain or head injury.
Based on data from the American Autonomic Society and the Mayo Clinic
