Strabismus

What is Strabismus?

Strabismus is a common and treatable eye condition in which one or both eyes are misaligned, often causing double vision, loss of depth perception, and other issues. Although Strabismus can occur at any age, it’s most frequently seen in infants and children. In children, Strabismus may not cause double vision, but the brain may turn off vision in one eye, which can impact the brain/vision connection.

Sometimes called “crossed eyes,” or “squint,” Strabismus is classified according to the direction the eyes turn: inward turning is esotropia, outward turning is exotropia, upward is hypertropia, and downward is hypotropia. According to the American Association for Pediatric Ophthalmology and Strabismus (aapos.org), 4% of people living in the US have Strabismus, and the Mayo Clinic (mayoclinic.org) reports nearly one in twenty children in the US have Strabismus.

What causes Strabismus?

Strabismus is caused by faulty or weak eye muscles, a defect in the nerves that control them, and/or miscommunication between the muscles and the brain, causing a failure of the eyes to work in unison to focus on the same thing at the same time. The result is crossed eyes and double vision. Strabismus is often the cause of Amblyopia (“lazy eye”). Watch this Strabismus video from Johns Hopkins Medicine.

There is a genetic factor, so Strabismus sometimes runs in families. It can also be caused by refractive errors (nearsightedness, farsightedness, astigmatism, and anisometropia), premature birth, autism, Down syndrome, and neurological anomalies, including cerebral palsy. While Strabismus is one of the most common childhood eye diseases, adults can develop it due to conditions including thyroid eye disease (TED), stroke, vascular and neurological disorders, and head trauma. Untreated Strabismus can lead to vision loss.

Symptoms of Strabismus

Symptoms of Strabismus include eyes that do not move together, eyes that focus on two different points, poor depth perception, blurred vision, squinting or frequent blinking (especially in bright light), headaches, head tilting, and sensitivity to light.  When the eyes are misaligned, the brain receives mixed messages and gradually begins to ignore the misaligned eye, which then becomes weaker. In children, the brain may ignore input from one eye entirely.

How to Avoid Strabismus

Strabismus cannot be prevented, but complications, including vision loss, can be reduced with early diagnosis and treatment. Eye exams are a crucial way to check eye health, diagnose any diseases or conditions, and protect sight. Eye exam recommendations vary by age, any existing eye conditions, genetic predisposition, and other factors. The American Academy of Ophthalmology (AAO) provides comprehensive recommendations on the timing and frequency of vision screening and eye exams. Check these recommendations and discuss the ideal eye exam schedule with your doctor.

Types of Strabismus

There are many Strabismus variations, but of the estimated 13 million people in the US who have this eye alignment disorder, most have one of the following types, occurring intermittently or consistently:

• Esotropia: One or both eyes turn inward towards the nose. This condition can present at any age but is most frequently seen in infants. Sometimes, infants may appear to have esotropia, though their vision is fine (pseudostrabismus, more commonly seen in infants of East Asian and Native American descent). By about six months, as the baby’s skull continues to grow, the appearance of pseudostrabismus may disappear.
• Exotropia: One or both eyes turn outward towards the ears. This can happen at birth (congenital exotropia) or at any age and be constant or occasional (intermittent exotropia). Exotropia sometimes occurs following surgery to fix crossed eyes.
• Hypertropia: Also known as vertical Strabismus, hypertropia causes one eye to move higher than the other. Untreated hypertropia sometimes leads to Amblyopia (lazy eye).

Amblyopia Versus Strabismus

How are Amblyopia (lazy eye) and Strabismus related? While Strabismus is often the cause of Amblyopia, and the two often occur together, their causes are different. With Strabismus, the eyes are misaligned due to dysfunction among one or more of the six eye muscles, while Amblyopia is typically an early childhood development issue that results in weak visual acuity in one eye. Without treatment, over time, the brain may ignore the weak eye and focus on the stronger eye. The result may be blurry vision and faulty depth perception. Enjoy this Amblyopia video from Johns Hopkins Medicine.

How to Test for Strabismus

During a comprehensive eye examination, your optometrist or ophthalmologist will discuss patient history, check visual acuity (how well you see up close and at a distance) with the Snellen eye test (letter) chart, and assess the general health of your eyes using a variety of tools, which may include drops to dilate the pupils. To test for Strabismus, the eye doctor will conduct the light reflex test (also known as the Hirschberg test), the cover/uncover test, and the prism cover test (PCT) to diagnose the presence, type, and degree of misalignment.

Treatment for Strabismus

Treatment can often successfully correct Strabismus without surgery, aligning the eyes to improve both appearance and function. Several treatments can repair or minimize Strabismus, especially when diagnosed early, including:

• Eye exercises (orthoptic therapy), monitored in an optometrist’s office and continued at home for weeks or months, have proven effective in treating some forms of Strabismus.
• Eye drops or injections of botulinum toxin type A (i.e., Botox®) can be used to reduce the pull of hyperactive eye muscles.
• Prism eyeglasses are used to create a corrective refraction, bending incoming light to pull the unaligned eye into alignment.

Ongoing self-care for people who have Strabismus, or any eye condition, includes eye exercises, limiting screen time, getting adequate sleep, exposure to natural sunlight, staying physically active, and a diet rich in Vitamins A, C, E, and lutein.

Surgery for Strabismus

If treatments fail to correct misalignment, an ophthalmologist may recommend Strabismus surgery (also called eye muscle surgery), a common eye surgery in the US. In this outpatient surgery, the ophthalmologist adjusts the eye muscles, folding over those that are too slack and shifting those that are displaced or too short so that both eyes line up and focus on the same spot at the same time. Strabismus surgery is performed under local or general anesthesia in a hospital or surgery center. Surgery typically takes up to two hours and has a high success rate. Recovery time is generally a few days, and success includes improved vision and corrected physical alignment. In some cases, surgery may improve the physical alignment of the eyes without improving vision.

In summary, Strabismus is a prevalent and treatable eye condition that affects both children and adults. It can lead to misaligned vision, depth perception issues, and potential long-term complications if left untreated. Early diagnosis through comprehensive eye exams is key to preventing vision loss caused by Strabismus.  Once diagnosed there are a range of treatments, including eye exercises, corrective lenses and surgery that can effectively correct Strabismus, helping individuals maintain healthy vision.