Your patient’s transient darkening of vision in one eye sounds like amaurosis fugax. ‘Amaurosis’ is Greek for ‘darkening’ and ‘fugax’ is Latin for ‘fleeting’. It describes a temporary loss of vision through one eye for a few seconds which returns to normal after a few minutes. This is often due to a temporary disturbance of the blood flow to the back of the eye.

Amaurosis fugax is not a disease but a sign of disease. One cause is when a blood clot or a piece of plaque blocks an artery in the eye. The blood clot or plaque usually travels from a larger artery, such as the carotid artery in the neck or an artery in the heart, to an artery in the eye.

Plaque is a hard substance that forms when fat, cholesterol and other substances build up in the walls of arteries.

The problem is that amaurosis fugax can also occur because of other disorders:

• Optic neuritis
• Blood vessel disease
• Migraine headaches
• Brain tumour
• Head injury
• Multiple sclerosis
• Systemic lupus erythematosus, an autoimmune disease in which the body’s immune cells attack healthy tissue throughout the body.

It is difficult for an eye specialist to diagnose the cause of the amaurosis fugax and your patient deserves a referral to his general practitioner for blood and other tests to be arranged with the appropriate specialists.