Eye Deviation: Causes and When to Worry

What eye deviation means

Six muscles move each eye. The brain coordinates them through three cranial nerves (the third, fourth and sixth) so both eyes point at the same object. When the muscles, the nerves, the brain's control centers or the eye socket are affected, one eye drifts. Doctors describe it by direction:

A tropia is visible all or much of the time. A phoria is a hidden tendency that the brain normally controls and that shows only when one eye is covered or you are tired.

Gaze deviation is different: both eyes turn together to one side, as in a stroke or seizure. It is always an emergency.

Eye deviation in babies and children

• Normal newborn wandering: brief crossing or drifting is common in the first 3 to 4 months while coordination develops.
• Pseudostrabismus: a wide, flat nasal bridge and skin folds make the eyes look crossed when they are actually straight. An eye doctor can confirm this with a light-reflex test.
• Infantile esotropia: a large inward turn starting before 6 months.
• Accommodative esotropia: inward turning from about age 2 to 3 because of farsightedness. Glasses often straighten the eyes.
• Intermittent exotropia: an eye drifts out when tired, ill or looking far away, and often squints closed in sunlight.
• Serious but rare causes: a cataract, retinoblastoma (an eye cancer that may show as a white pupil in photos), or raised pressure inside the head.

Children rarely complain of double vision, because the brain ignores the image from the turned eye. That eye then fails to develop full vision, causing amblyopia (lazy eye). Treatment is most effective before about age 7 to 8, so a constant turn at any age, or any turn after 4 months, should be checked.

Causes of eye deviation in adults

Adults usually notice double vision, which goes away when either eye is covered.

Cranial nerve palsies

A cranial nerve palsy weakens specific eye muscles:

• Third nerve palsy: the eye turns down and out, the eyelid droops and the pupil may be large. With a large pupil and headache, an expanding brain aneurysm must be ruled out the same day.
• Fourth nerve palsy: one eye sits higher. Often after head injury, or present from birth and noticed later. People tilt their head to compensate.
• Sixth nerve palsy: the eye cannot turn outward, so it crosses in, with double vision worse at distance. Causes include raised intracranial pressure, as well as diabetes.

In people over 50 with diabetes or high blood pressure, small-vessel damage to the nerve is the commonest cause, and it usually recovers within 3 months.

Other adult causes

• Thyroid eye disease: swollen, stiff eye muscles cause bulging eyes and deviation, most often limiting upward gaze.
• Myasthenia gravis: variable deviation and drooping eyelids that worsen through the day.
• Stroke, multiple sclerosis and brain tumors: affect the brainstem pathways.
• Orbital fracture: a blow to the eye can trap a muscle, especially limiting upward gaze.
• Decompensated childhood squint: a lifelong phoria that the brain can no longer control.
• After eye surgery: cataract or retinal surgery occasionally disturbs alignment.

How doctors assess eye deviation

An eye doctor (ophthalmologist or optometrist) will:

1. Ask when it started, whether it is constant, and whether there is double vision, headache or other symptoms.
2. Look at old photos to see how long the deviation has been present.
3. Perform the cover test, covering each eye in turn and watching whether the other moves to refocus.
4. Measure the angle of deviation with prisms.
5. Check eye movements in all directions, eyelids and pupils.
6. Check vision and glasses prescription, and examine the back of the eye.

New adult cases may need an urgent MRI or CT scan, blood sugar, thyroid tests and antibody tests for myasthenia gravis.

Treatment

• Glasses: correct farsightedness and can fully straighten accommodative esotropia.
• Patching or atropine eye drops: force a child to use the weaker eye to treat amblyopia.
• Prism glasses: shift images to relieve double vision in adults.
• Eye muscle surgery: tightens or loosens muscles to realign the eyes. It is usually a day procedure with a high success rate, though some people need more than one operation.
• Botulinum toxin injection: temporarily weakens an overacting muscle.
• Treating the cause: controlling diabetes or thyroid disease, myasthenia treatment, or neurosurgery for an aneurysm.

Many nerve palsies from small-vessel disease improve by themselves. Surgery is usually delayed for 6 months or more until the deviation is stable.

Frequently asked questions

What is eye deviation?

Eye deviation is when one or both eyes point in a different direction from the target, turning in, out, up or down. The medical term for misaligned eyes is strabismus. When both eyes turn together to one side, doctors call it gaze deviation, which suggests a stroke or seizure.

Is it normal for a baby's eyes to deviate?

Brief wandering or crossing is normal in the first 3 to 4 months. After 4 months, or if the eye turn is constant at any age, see a pediatrician or eye doctor. Early treatment prevents lazy eye and permanent loss of vision in the turned eye.

Can eye deviation in adults be serious?

Yes. A new eye deviation in an adult usually causes double vision and needs prompt assessment. With a severe headache, a drooping eyelid, a large pupil or stroke symptoms, call 911, because it may be an aneurysm or stroke.

Can strabismus be fixed in adults?

Yes. Adults can have prism glasses, Botox injections or eye muscle surgery at any age. Surgery improves alignment, relieves double vision in most people, and can help depth perception and confidence. It does not restore vision lost to childhood amblyopia.

Why do eyes deviate to one side during a stroke or seizure?

Both eyes are controlled by gaze centers in the brain. A stroke usually makes the eyes look toward the damaged side of the brain, while a seizure can drive them away from it. Either is an emergency.