Sometimes when I hold my breath I lose vision in my left eye—is that normal?

Losing vision in one eye, even temporarily, is never normal. Amarosis fugax, or fleeting blindness, requires an immediate full eye exam, and usually a neurological and cardiac evaluation. Ophthalmologists often see patients who have nothing wrong with the eye itself, but have ocular symptoms of brain or heart disease.

You didn't mention your age. In older people, temporary loss of vision in one eye can be a symptom of atherosclerotic disease (narrowing of the carotid artery) or inflammation of the blood vessels (temporal arteritis), which can lead to stroke. Immediate diagnosis, work-up, and treatment is important to prevent permanent loss of vision.

In all age groups, transient loss of vision can be caused by hyperviscosity (increased thickness) of the blood, multiple sclerosis (a disease that disrupts the flow of information within the brain, and between the brain and the body), complex migraine, lupus (when the body attacks its own tissues), heart valve abnormalities, brain tumors, and heart arrhythmias (irregular heartbeat). High pressure inside the skull (pseudotumor cerebri) can occur in anyone, but is often seen in young, obese women. Malignant hypertension (high blood pressure) and lupus can occur at any age.

Your ophthalmologist is a medical doctor who has a complete understanding of cardiac and neurological disease that can cause ocular symptoms. Schedule an appointment immediately with your ophthalmologist, who will want more detail about your symptoms—when they started, when they occur, how long the symptoms last—and also a complete past medical history, and a complete eye exam looking at your vision, visual field, color vision, and if there is any abnormality of the eye such as retinal detachment or swelling of your optic nerve (papillema) which can mean high pressure inside the skull.

Depending on your eye exam, you might need further testing of your brain (MRI/spinal tap with opening pressure), or carotid arteries (carotid ultrasound), or of your heart valves (cardiac ultrasound) or heart rhythms (Holter Monitor, EKG), and blood testing for inflammation and hypercoagulability.