Eye Alignment Disorder (Strabismus)

How the eyes stay aligned

Each eye is moved by six muscles controlled by three cranial nerves. The brain coordinates them so both eyes look at the same point, then fuses the two images into one 3D picture. Strabismus happens when the muscles, the nerves controlling them, or the brain's coordination system do not work properly.

Types of strabismus

Strabismus can be constant or intermittent, and can affect one eye or alternate between eyes.

Strabismus in children

Causes and risk factors

• farsightedness (hyperopia): focusing effort drives the eyes inward (accommodative esotropia), typically starting between 1 and 4 years
• family history
• prematurity and low birth weight
• neurological conditions: cerebral palsy, Down syndrome, hydrocephalus
• eye problems that reduce vision in one eye: cataract, retinal disease, and rarely retinoblastoma

Why early treatment matters

A child's brain may ignore the image from the turned eye to avoid double vision. Over time, that eye's vision fails to develop, causing amblyopia (lazy eye). It is most treatable before about age 7 to 8. Children also lose depth perception if alignment is not restored early.

Newborns' eyes may wander intermittently until about 4 months of age. A constant turn at any age, or any turn after 4 months, should be checked.

Strabismus in adults

New misalignment in adults usually causes double vision, because the adult brain cannot suppress the second image. Causes include:

• cranial nerve palsies: from diabetes, high blood pressure, head injury, aneurysm or tumor. A third nerve palsy with a large pupil and droopy eyelid is an emergency
• thyroid eye disease: swollen eye muscles restrict movement
• myasthenia gravis: variable double vision and droopy eyelids, worse with tiredness
• stroke and multiple sclerosis
• orbital fractures and eye surgery
• childhood strabismus that returns or worsens with age

Symptoms

• eyes visibly pointing in different directions
• double vision (mainly adults)
• squinting or closing one eye, especially in bright light
• tilting or turning the head to see better
• eye strain, headaches and tiredness when reading
• poor depth perception

Diagnosis

An eye examination by an ophthalmologist or optometrist includes:

• cover tests: covering each eye in turn to see whether the other moves to refocus
• corneal light reflex test: checking whether light reflects in the same spot in both pupils
• measuring the angle of misalignment with prisms
• refraction with dilating drops to detect farsightedness in children
• checking each eye's vision for amblyopia
• a full eye health exam

Adults with sudden onset may need blood tests, myasthenia gravis antibody tests, thyroid tests, and brain MRI or CT angiography.

Treatment

Glasses

Glasses that correct farsightedness can fully straighten accommodative esotropia.

Treating amblyopia

• patching the stronger eye for some hours each day
• atropine drops to blur the stronger eye
• digital and binocular therapy in some cases

Prism glasses

Prisms bend light so both eyes see a single image. They help small, stable deviations and double vision in adults.

Eye muscle surgery

Surgery loosens or tightens specific eye muscles to realign the eyes. It is a common, usually outpatient procedure, and more than one operation is sometimes needed. Adults with long-standing strabismus benefit too: surgery improves appearance, comfort, and often depth perception and field of view.

Other options

• Botulinum toxin injections into an eye muscle to weaken it, mainly for some esotropias and nerve palsies
• Vision therapy and convergence exercises for convergence insufficiency
• Treating the cause in adults: managing diabetes or thyroid disease, or treating myasthenia gravis. Many nerve palsies from diabetes recover within 3 to 6 months

Frequently asked questions

What is an eye alignment disorder?

An eye alignment disorder, or strabismus, is a condition in which the eyes do not look in the same direction at the same time. One eye may turn in, out, up or down. It can be constant or come and go, and can occur in children or adults.

What causes strabismus in adults?

In adults, new strabismus is often caused by nerve damage from diabetes or high blood pressure, thyroid eye disease, stroke, head injury, myasthenia gravis, or the return of childhood strabismus. Sudden onset with double vision needs prompt medical evaluation.

Can strabismus be corrected without surgery?

Sometimes. Glasses can fully correct strabismus caused by farsightedness, prisms can help small deviations, convergence exercises help some outward turns, and Botox injections can be used for certain types. Larger or persistent misalignments often need surgery.

Is strabismus the same as lazy eye?

No, though they are linked. Strabismus is misalignment of the eyes. Lazy eye (amblyopia) is reduced vision in one eye because the brain favors the other. Strabismus is a common cause of amblyopia in children, which is why early treatment is important.

When should I worry about my baby's eyes crossing?

Occasional crossing or wandering is normal in the first 4 months. See a doctor if the eyes cross or drift constantly at any age, or at all after 4 months, or if you notice a white reflection in the pupil in photos.