Understanding Strabismus (Crossed Eyes): Types, Causes, Symptoms & Modern Treatment Options

What Is Strabismus?

Strabismus, commonly known as crossed eyes or squint, is an eye condition in which both eyes do not point in the same direction at the same time. One eye may turn inward, outward, upward, or downward while the other eye remains properly aligned.

Because the eyes fail to work together, strabismus can interfere with binocular vision, depth perception, and overall visual clarity. This condition can affect infants, children, and adults, and without treatment, it may lead to long-term vision problems.

Globally, strabismus affects a significant portion of the population—occurring in up to 5–6% of children and around 4% of adults, with higher prevalence in people over 60 years of age.

How Normal Eye Alignment Supports 3D Vision

For clear and accurate vision, both eyes must align precisely on the same object. Light entering the eyes is focused through the cornea and lens onto the retina, which then sends signals to the brain. The brain combines these two images into a single, three-dimensional view.

When eye alignment is disrupted:

• Children’s brains may suppress the image from one eye, leading to reduced vision

• Adults may experience double vision (diplopia)

• Depth perception (stereopsis) becomes impaired

Types of Strabismus

Strabismus is classified based on eye direction, frequency, and age of onset.

1. Classification by Eye Direction

Horizontal Strabismus

Esotropia (Inward Turning Eye)

• Alternating esotropia: Eyes take turns deviating inward

• Accommodative esotropia: Linked to farsightedness and often corrected with glasses

• Non-accommodative esotropia: Eye deviation remains unchanged despite glasses

• Near esotropia: Occurs only when focusing on close objects

Exotropia (Outward Turning Eye)

• Sensory exotropia: Develops in an eye with poorer vision

• Alternating exotropia: Both eyes drift outward at different times

• Unilateral exotropia: One eye consistently turns outward

• Consecutive exotropia: Occurs after surgery for esotropia

Vertical Strabismus

• Hypertropia: One eye turns upward

• Hypotropia: One eye turns downward

These forms are more commonly diagnosed in childhood.

2. Classification by Frequency

• Constant strabismus: Eye misalignment is present all the time

• Intermittent strabismus: Misalignment occurs occasionally

3. Classification by Age of Onset

• Congenital (Infantile) Strabismus: Appears before 6 months of age

• Acquired Strabismus: Develops after infancy due to medical or visual causes

What Causes Strabismus?

Strabismus can develop due to a variety of factors, including:

• Imbalance or weakness of eye muscles

• Uncorrected refractive errors (farsightedness, nearsightedness, astigmatism)

• Hyperopia (farsightedness) causing excessive focusing effort

• Neurological conditions such as stroke or brain tumors

• Systemic diseases like diabetes or thyroid disorders

• Increased eye pressure, sometimes after eye surgery

• Retinoblastoma, a rare childhood eye cancer

Why Does Strabismus Occur in Newborns?

In infants, strabismus may result from:

• Genetic inheritance

• Congenital syndromes (e.g., Down syndrome, cerebral palsy)

• Delayed neuromuscular eye control

Early evaluation is essential to prevent vision loss.

Common Symptoms of Strabismus

Signs and symptoms may include:

• Crossed or wandering eyes

• Double or blurred vision

• Eye strain and frequent headaches

• Head tilting or squinting

• Difficulty judging distances

Symptoms often appear before age 6, but adults may develop strabismus later in life.

Strabismus vs. Pseudostrabismus

Some children appear cross-eyed but actually have pseudostrabismus, a harmless condition caused by facial features such as:

• Wide nasal bridge

• Prominent epicanthal folds

An eye specialist can differentiate the two using light reflex tests and cover tests. In pseudostrabismus, eye alignment is normal.

Possible Complications of Untreated Strabismus

If not treated early, strabismus can lead to:

• Amblyopia (lazy eye) — permanent vision loss in one eye

• Poor depth perception

• Learning difficulties in children

• Driving and coordination problems in adults

• Low self-confidence, anxiety, or depression

How Is Strabismus Diagnosed?

An ophthalmologist may perform:

• Corneal light reflex (Hirschberg) test

• Cover and uncover tests

• Cycloplegic refraction to detect hidden refractive errors

• Visual acuity testing

• Ocular motility evaluation to assess eye movement coordination

Treatment Options for Strabismus

Treatment depends on age, cause, and severity.

Non-Surgical Treatments

• Prescription glasses or contact lenses

• Prism lenses (especially helpful for adults with double vision)

• Vision therapy and eye exercises

• Eye patching for amblyopia in children

• Botulinum toxin injections to temporarily weaken overactive muscles

• Orthoptic exercises before or after surgery

Strabismus Surgery

Surgery is recommended when non-surgical treatments are insufficient. It involves adjusting eye muscle position to restore alignment and improve binocular vision.

Recovery and Aftercare

• Healing may take up to 12 weeks

• Eye drops and mild pain relief are prescribed

• Avoid driving, swimming, and hot tubs for at least 2 weeks

Potential Surgical Risks

• Infection or bleeding

• Recurrence of misalignment

• Temporary or persistent double vision

• Drooping eyelids or scarring

Advances in Strabismus Treatment

Modern innovations include:

• 3D computer-assisted surgical planning

• Adjustable sutures for precise post-operative correction

• Virtual reality-based vision therapy

• Computer-guided eye coordination programs

Living Well With Strabismus

Daily coping strategies include:

• Regular eye examinations

• Consistent use of prescribed treatments

• Home-based eye exercises like pencil push-ups

• Psychological support when needed

Reliable educational resources are also available through organizations such as the American Association for Pediatric Ophthalmology and Strabismus, which offers guidance for patients and families.