Oculocardiac reflex

How it works

Pressure on the eyeball, or a pull on one of the muscles that turn the eye, slows the heart¹. The signal starts in the ciliary nerves of the eye. It travels along the trigeminal nerve, the main nerve of feeling in the face, to the brainstem. The brainstem answers through the vagus nerve, which acts as a brake on the heart¹.

Doctors count it as the reflex when the heart rate drops by more than 20%¹. Usually it does no harm¹. In rare cases the heart pauses completely, or its rhythm goes wrong¹². The reflex also tires. A second pull soon after the first gives a smaller drop¹².

It belongs to the trigeminovagal reflexes, a family that also includes the diving reflex². In a study of 30 healthy people, a measured press on the eye lowered heart rate by 10% on average. Setting off the diving reflex lowered it by 23%, but more slowly².

How common it is

Healthy people have it too². The numbers come from eye surgery, where heart rate is watched closely. The main example is strabismus surgery, an operation on the eye muscles to straighten a squint. Studies find the reflex in 14–90% of these operations¹³. The range is wide because studies define and measure it differently³. One study of 99 patients found it in 65%³. A study in Alaska, with no preventive drug, found a drop of more than 20% in 41% of patients². The reflex is stronger in children and weakens with age¹².

Is it a problem?

No, not in daily life. It matters during eye surgery. Do not press on your eyes to slow your heart.

Without a preventive drug, the heart slows a lot in almost 10% of squint operations². A drug such as atropine, given before the operation, makes the reflex much less likely¹².

Pressing on the eyeball to slow the heart is dangerous. It can injure the eye⁴. In a few cases it has caused a fatal heart rhythm⁵. The gentle, brief press in the phosphenes entry is not a way to slow the heart. Hard or long pressure is what carries the risk.

History and culture

Two doctors, Aschner and Dagnini, described the reflex separately in 1908¹². The title of Aschner’s paper describes the pulse at the wrist disappearing when the eye is pressed².

Doctors once pressed on the eyes to stop a sudden racing heart, called supraventricular tachycardia⁴⁶. They now avoid it because it can injure the eye⁴. In one reported case, eye pressure turned a man’s fast heart rhythm into a more dangerous one. He needed an electric shock⁶.