What Is the Corneal Reflex?
A Reflex That Protects Your Eye From Damage
Medically reviewed by Priscilla Vu, MD
The corneal reflex is also sometimes referred to as the eye-blink reflex. This reflex causes you to blink if something touches your eye, and it serves to protect your eye from surface damage.
Corneal reflex testing is often part of a neurological examination. If this reflex is impaired and your eye doesn’t blink when something touches it, you may have nerve, brain, or eye disease.
This article will discuss how to test the corneal reflex, what to expect in testing, what an absent corneal reflex might mean, and when to see a healthcare provider.
Maria Kraynova / EyeEm / Getty Images
How to Test the Corneal Reflex
The corneal reflex test can be done while you are awake. Your healthcare provider might do this during an office medical visit or during an eye appointment by gently placing a clean object (like the soft tip of a cotton swab) on your eye. If you blink, this is a sign that your corneal reflex is working.
The reflex may also be tested in a hospital setting, while a person is asleep, not conscious, and unaware of the test. During a corneal reflex test when a person is not alert, the eyelid is held open, and a clean object—such as the soft head of a cotton swab—is brought to the eye to see if the person will blink.
In this setting, the corneal reflex is important for assessing brain activity, and it can help determine the severity of brain damage.
What Is the Cornea?
The cornea is the clear, protective outer layer that covers the iris, pupil, and anterior chamber of the eye. The corneal reflex is triggered by anything touching the thin top layer of the cornea. The conjunctiva is a thin layer of protective tissue that covers the white part of the eye.
What to Expect
If your healthcare provider is testing your corneal reflex, there is no need for you to do anything. A corneal reflex test is safe and quick.
Your healthcare provider will describe the test briefly and may hold your head gently so you won’t move it—moving your head can cause an eye injury if you move toward the object.
They will bring the object to one eye, and both eyes should blink rapidly. They then will bring the object to your other eye—and, again, both eyes should blink rapidly.
Sometimes people will blink when an object nears the eye. That’s because there is another blink reflex that occurs when something comes near the eye. Relaxing can help prevent this so your healthcare provider can complete your corneal reflex test.
Often, the corneal reflex test will also cause tears to flow from both eyes. That’s because another part of your reflex response to having something in your eyes is a flow of tears, which helps to wash out any material from your eyes.
What Does Absence of Corneal Reflex Indicate?
The corneal reflex is an involuntary (not on purpose) muscle movement. It works because of rapid reflex communication between the trigeminal nerve, which is the fifth cranial nerve, and the facial nerve, which is the seventh cranial nerve. It also relies on sensory nerve endings on your cornea and on your ability to move the muscles of the eyelid.
An absence of the corneal reflex can indicate a problem with either the fifth or seventh cranial nerve, or a problem with the cornea or with the muscles that control the eyelid.
Conditions that can cause a diminished or absent corneal reflex include:
Bell’s palsy: A condition of weakness of one side on the face, which usually resolves on its own
Glaucoma: A group of conditions causing increased pressure in the eye that can damage the optic nerve
Neurotrophic keratopathy: A disease that causes degeneration of the cornea and loss of corneal sensation
Multiple sclerosis: A condition in which the immune system mistakenly attacks the myelin sheath that covers nerve fibers
Stroke: A blockage of blood flow or bleeding in the brain
Brain tumor: An abnormal growth in the brain
Brain swelling
Muscle paralytics: Medications such as those used for surgical anesthesia
These conditions do not always affect the corneal reflex. This test is one part of the diagnostic process that is used along with other diagnostic testing to make a diagnosis.
When to See a Healthcare Professional
Generally, loss of the corneal reflex would not occur on its own—it would be one of several symptoms of a health problem.
You should get medical attention if:
You are having trouble opening or closing one or both of your eyes.
One or both of your eyelids is droopy.
You are not seeing clearly from one or both eyes.
You have noticed one or more blind spots or problems with your peripheral vision.
You have constant or intermittent double vision.
Summary
The corneal reflex is the rapid eye blink that happens when anything touches the surface of your eye.
This involuntary action occurs rapidly because there is a connection between the sensory nerve of the eye (trigeminal nerve, cranial nerve 5) and the nerve that controls motor movement of the eyelid (facial nerve, cranial nerve 7) that does not rely on awareness or deliberate movement.
This reflex protects your eye from the harm that could occur if an object gets on the surface of your eye. An absent corneal reflex can be a sign of eye disease, disease of cranial nerves 5 or 7, or a brain disorder.
Usually, the corneal reflex works without a problem, but serious medical or eye conditions can affect the corneal reflex.
If your healthcare provider has diagnosed you with an impaired corneal reflex, it’s important that you take precautions to protect your eyes. This can include wearing eyeglasses as a shield, even if you don’t need them for vision correction. Make sure you maintain regular eye appointments so that any damage or harm to your eye can be diagnosed and taken care of promptly.
Frequently Asked Questions
What does the corneal reflex test for?
The corneal reflex is part of an eye exam or a neurological exam. It tests how the following function:
Sensory nerve endings on the cornea
Cranial nerve 5
Cranial nerve 7
Muscle movement of the eyelids
These need to be healthy for the corneal reflex to work properly.
What triggers corneal reflex?
The corneal reflex is triggered by having something touch the surface of the cornea.
Why is the corneal reflex important?
This reflex protects your eye from damage. The rapid blinking prevents objects from harming your eye, and the associated tears help to wash out debris from the surface of the eye.
