Strabismus (Crossed Eyes)

What is Strabismus?

Strabismus, also known as tropia or crossed eyes, is a condition that causes eye misalignment. The eyes point in different directions and do not line up.⁴

In some cases of crossed eyes, one eye looks straight out while the other eye turns in or out, up or down. In other cases, both eyes turn in or out, up or down.

With normal vision, both eyes look in the same direction. The brain combines the views from both eyes into a single image with depth perception.

All six eye muscles must move together to focus on an image.^{1, 6} With strabismus, they don’t. But the brain needs both eyes to see correctly. Therefore, strabismus takes a toll on vision.

Types of Strabismus

There are four main types of strabismus:²

1. Esotropia (when the eyes turn inward)
2. Exotropia (when the eyes turn outward)
3. Hypertropia (when the eyes turn upward)
4. Hypotropia (when the eyes turn downward)

The two most common forms of strabismus are:²

1. Accommodative esotropia. This tends to happen when farsightedness is left untreated. It may also be genetic.
2. Intermittent exotropia. This is when one eye fixates on an object, while the other eye points outward. The eye turn is only present sometimes.

For most children with strabismus, the cause is unknown. More than half of strabismus cases in children are present at or right after birth. This is known as congenital strabismus.

What are the Symptoms of Strabismus?

Some people with strabismus may not experience any symptoms. Others experience all or some of the following:²

• Eye position changes (upward or downward turning)
• Blurry vision
• Difficulty seeing close-up objects
• Difficulty seeing far-away objects
• Trouble seeing visual images at any distance
• Double vision
• Headaches
• Squinting to see
• Eyestrain
• Using just one eye to see
• Tilting or turning the head to see
• Struggling to control eye movement
• Sensitivity to bright sunlight in the misaligned eye
• Poor vision development in infancy

What Causes Strabismus? 

Here are a few causes of strabismus in adults:^{1, 6}

• Medical conditions like diabetes or thyroid disease
• Brain tumors
• Stroke
• Trauma that affects the head or damages the eyes
• Eye surgery
• Botulism
• Graves disease
• Guillain-Barre syndrome
• Family history
• Eye disease

Some other disorders are also associated with crossed eyes in children. These include:^{5, 6}

• Cerebral palsy
• Down syndrome
• Congenital rubella
• Prader-Willi syndrome (PWS)
• Incontinentia pigmenti syndrome (causes skin, hair, eye, teeth, and central nervous system (CNS) abnormalities)
• Apert syndrome (causes skull, hand, feet, and face abnormalities)
• Retinopathy of prematurity (ROP)
• Retinoblastoma (retina cancer)
• Trisomy 18 (Edward’s syndrome)
• Hemangioma close to the eye
• Noonan syndrome

Potential Risks of Strabismus

If strabismus is left untreated, it can cause more severe vision problems.

For example, strabismus can cause a lazy eye (amblyopia). A lazy eye has weaker muscles. The brain uses the stronger eye more, worsening the weaker eye over time.

Strabismus can also cause health issues related to poor vision. This includes headaches or injury from difficulty seeing.

When to See a Doctor

Visit a doctor if you are having trouble seeing clearly. You should also see a doctor if the worsening vision issues are not improving with treatment. 

If you are worried about your child’s eyesight, reach out to your doctor right away. If your child is at least 3 months old, and their eyes are misaligned, schedule an eye exam. Even if their eyes only appear misaligned at times, get them checked.⁴

Most children who develop strabismus are diagnosed between the ages of 1 and 4 years old. Some children develop strabismus after age 6 due to other health conditions.³

Diagnosis

Your doctor will perform an eye exam to diagnose you or your child with strabismus. During an eye exam, the doctor will assess visual acuity. This includes depth perception and how well you can see letters or numbers at different distances.

They will also perform a retinal exam and a neurological exam.⁴

Treatment

Treatment for strabismus varies depending on the cause, the price, and your candidacy, among other factors.

Here are some treatment options that your doctor may recommend:

• Eyeglasses or contact lenses can treat refractive errors that cause strabismus. If you are struggling to see far-away objects, which can cause intermittent exotropia, prescription lenses can help.⁷
• Your doctor may recommend prism lenses. These are special lenses that can help bend light to reduce how much the eye turns to view objects.

• Certain medications like eye drops, as well as botulinum toxin type A (Botox), can treat strabismus. These medications weaken overactive muscles in the eye. 
• Orthoptics are eye muscle exercises. Vision therapy exercises can strengthen certain eye muscles and improve control of eye misalignments.² 
• Eye muscle surgery changes the length or position of the eye muscles to align them. Strabismus surgery is done under general anesthesia.⁷ 
• Eye patches can treat lazy eyes caused by strabismus. Eye patches cover the stronger eye to strengthen the muscles in the weaker eye. This also improves eye movement control.⁷

Outlook

The outlook for strabismus is positive if it is treated early. Treatment can improve symptoms like double vision, difficulty understanding depth perception, and vision loss.

If strabismus is left untreated, it can lead to more vision issues down the line.²

Strabismus can cause amblyopia when the brain starts to ignore the affected eye and favors the healthy eye. Amblyopia can also cause strabismus.⁶

Summary

Crossed eyes are a common eye problem that can affect vision. If you or someone you know is struggling with strabismus, talk to an eye doctor.

Your eye doctor will run tests to diagnose any vision issues and treat them accordingly. Leaving strabismus untreated can cause more sight issues later on.