Strabismus (Crossed Eyes): Symptoms, Causes, & Treatments

Strabismus (squint eye or crossed eyes) is a type of eye misalignment in which both eyes point in different directions or do not align (line up) with each other. 

In healthy people, six muscles control eye movement and keep the eyes looking in the same direction. Strabismus occurs due to a problem with the nerve signals that control eye movement and these muscles. It causes one eye to turn in, out, up, or down (in a different direction from the other eye). 

The eye turning can be present all the time or only during periods of stress, such as eye strain, generalized fatigue, or illnesses.

Common Terms Associated with Strabismus 

Various terms are used to describe strabismus, including squint eye, cross eyes, cross eyed, crossed eyes, and cross-eyedness.  

Types of Strabismus

Strabismus is categorized in various ways, including:

Direction of Eye Turning: 

• Horizontal strabismus

  • Esotropia: Inward turning

  • Exotropia: Outward turning

• Vertical strabismus

  • Hypertropia: Upward turning

  • Hypotropia: Downward turning

Frequency of Eye Turning:

• Constant: Eye turning is present all the time

• Transient or intermittent strabismus: Eye turning occurs when the person has done a lot of reading or is tired or ill

Eye Involved:

• Unilateral: Eye turning always involves the same eye

• Alternating: Eye turning involves the right eye at times and the left eye at other times

Cranial Nerve Involved:

• Third nerve (III) palsy 

• Superior oblique (IV) palsy

• Abducens nerve (VI) palsy

Type of Strabismus:

• Accommodative esotropia: This type of strabismus develops due to uncorrected farsightedness (there is extra effort required to focus on distant objects and the eye points in as a result). Other risk factors include a family history of esotropia (eyes that turn in). 

• Intermittent exotropia: One eye fixates on an object while the other alternates between pointing outward and looking straight.

• Infantile esotropia: Babies under 6 months of age have significant turning in both eyes. This is intermittent at first but later becomes constant. Glasses do not correct the eye crossing. Strabismus surgery can correct eye misalignment.

Prevalence and Demographics

According to the American Association for Pediatric Ophthalmology and Strabismus, almost 1 in 20 kids and approximately 4% of the U.S. population (around 13 million people) have strabismus. This eye condition usually occurs in children, but can also occur in adults. 

Age at Onset and When to See an Ophthalmologist

Newborn babies often have wandering eyes, but this is temporary. Most babies can focus on small objects by the time they are 3-4 months old. By age 6 months, a baby with normal vision should be able to focus light with his or her eyes straight and with the eyes aligned.

When strabismus is present, it usually appears before age 3 in children. In more than half the cases, strabismus is present at or shortly after birth - this is called congenital strabismus.

Sudden development of strabismus (especially with double vision) in an older child or adult can be a sign of a serious neurological disorder and should be evaluated by a healthcare professional without delay. 

Pseudostrabismus (False Strabismus)

Pseudostrabismus (false strabismus) is a condition that makes a baby look cross-eyed even though there are no problems with the eye muscles. It occurs because of extra skin at the inner corners of the eyes or a flat or wide nasal bridge. Pseudostrabismus usually disappears on its own as the baby’s face grows. 

Symptoms and Diagnosis  

Recognizing the Signs of Strabismus  

• Diplopia (double vision)

• Closing or covering one eye when looking at close objects

• Closing or covering one eye when looking at distant objects 

• Frequent blinking in bright sunlight or bright light

• Tilting or turning the head

• Ptosis (droopy eyelid)

• Eye strain

• Headache

• Difficulty reading

Diagnostic Procedures and Tools: How is Strabismus Diagnosed?

Any child above the age of 4 months who appears to have cross eyes (strabismus) should be seen by a pediatric ophthalmologist for a complete eye examination. The eye doctor will obtain a medical history, family history, and medication history. They will also do the following eye tests to diagnose strabismus: 

• Visual acuity (by having a young child read letters and numbers on an eye chart).

• Refraction (by using a series of corrective lenses to see effects on focusing).

• Eye coordination, focusing, and alignment tests.

• Dilated eye exam (instilling eye drops to widen the pupils) to see the internal eye structures in more detail.

Before the eye doctor appointment for strabismus symptoms, it will help to note down the following information: 

• How long have the cross eyes been present?

• Did cross eyes develop suddenly or slowly over time?

• Is the child cross-eyed in one eye, or do the crossed eyes alternate?

• How severe is the cross-eyedness (mild, moderate, or severe eye turning)?

• Are the crossed eyes always present or only at times?

• Do other people in the family have a history of crossed eyes?

Importance of Early Detection

The symptoms of strabismus do not go away on their own without treatment and can get worse over time. 

It’s important to get a proper diagnosis and strabismus treatment because left untreated, this eye condition can cause serious complications. Also, sometimes, cross eyes are due to an underlying condition such as a brain tumor or eye tumor (for example, retinoblastoma), which may go undiagnosed and untreated if strabismus is not evaluated by a healthcare professional.

What Are The Long-Term Effects of Strabismus?

Some of the problems that can occur if you don’t treat strabismus include:

• Amblyopia or lazy eye (permanent decreased vision in the turned eye). This happens because the brain receives two separate images from the left and right eye. To prevent double vision, the brain starts ignoring the image from the turned eye. Over time, it results in poor vision development in that eye. 

• Double vision (seeing two images of a single object). This can make tasks like reading, writing, and driving difficult.

• Blurred vision, which can increase the risk of injuries and accidents. Blurry vision can also affect school and work performance and the ability to enjoy hobbies and leisure activities.

• Poor stereopsis (depth perception, three-dimensional (3D) vision, or binocular vision).

• Eye strain.

• Tiredness.

• Headaches.

• Lack of confidence and low self-esteem due to embarrassment about the appearance of cross eyes.

Causes and Risk Factors  

What is the Main Cause of Strabismus?

In most cases, strabismus develops due to neuromuscular problems with controlling eye movement that originate in the brain. However, sometimes cross eyes are due to problems with the eye muscles themselves. 

Certain risk factors can increase the chances of developing strabismus, including:

Eye Conditions

• Uncorrected refractive errors (nearsightedness, farsightedness)

• Poor vision in one eye

Other Medical Conditions

• Cerebral palsy

• Down syndrome (20% to 60% of people with Down syndrome have cross eyes)

• Hydrocephalus (fluid buildup in the brain) 

• Brain tumors

• Eye tumors

Maternal and Pregnancy Risk Factors for Cross Eyes in Babies

• Maternal smoking during pregnancy

• Exposure to drugs during pregnancy

• Low birth weight

• Prematurity

• Connatal infections

• Neurologic diseases

• Advanced maternal age

Causes of Adult Strabismus

• Stroke (this is the leading cause of adult strabismus)

• Head injury

• Vascular problems

• Neurological disorders

• Thyroid eye disease (Graves’ disease)

• Untreated childhood strabismus 

• Cross eyes that were treated in childhood but came back

Genetic Influences

A family history of strabismus increases the risk that a child will develop strabismus. Approximately one-third of children with strabismus have a family member who also had the problem.

Treatment Options: How is Strabismus Treated?

Non-Surgical Treatments: Can Strabismus Be Corrected Without Surgery?  

Non-surgical treatment options for strabismus (misaligned eyes) include: 

• Eyeglasses or contact lenses to treat refractive errors. This helps to reduce the effort required to make the eyes focus.

• Prism lenses (special lenses) to bend light rays entering the eye and avoid double vision.

• Patching to treat lazy eye (amblyopia) that is present alongside strabismus. This helps to improve vision by forcing the brain to use the other eye (weaker eye). It may also improve eye misalignment.

• Orthoptics (eye exercises) for certain types of strabismus such as exotropia or convergence insufficiency. 

• Medications (ointments, eye drops) to relieve symptoms of strabismus.

• Injections such as botulinum toxin type A (Botox) to weaken overactive eye muscles. 

• Vision therapy to improve visual skills, eye comfort, and eye function by changing visual signal processing and understanding of visual information. A vision therapy program typically consists of monitored in-office and at-home eye exercises for several weeks or months. In addition to the exercises, devices such as training glasses (lenses), prisms, patches, and filters may be used. 

Surgical Treatment Options  

Eye muscle surgery or strabismus surgery is a surgical procedure in which the surgeon aligns the misaligned eye by changing the length and position of the eye muscles. This surgery is done under general anesthesia. Dissolvable stitches are typically used.

Note: Eye muscle surgery does not fix the poor vision related to amblyopia (lazy eye). The surgery will fail if amblyopia has not been treated. The child may still need to wear glasses after eye muscle surgery.

Advances in Medical Treatments and Therapies

Some recent advances in treating symptoms of strabismus include:

• Adjustable sutures: This technique allows more precise and customized correction of strabismus. It is done using temporary stitches that can be adjusted after the surgery to fine-tune eye alignment. 

• Lancaster Red-Green (LRG) test: This test helps doctors understand a patient’s eye misalignment better and plan surgery accordingly. It allows the eye surgeon to identify if a patient's straight-ahead vision has good alignment and if they can perform surgery without interfering with it. 

• AmblyGo: This at-home treatment for amblyopia (lazy eye) uses video game therapy to stimulate the weaker eye and ensure both eyes work together. It can be an engaging amblyopia treatment for children. 

• High-resolution MRI (magnetic resonance imaging): This imaging technique can provide important details about orbital anatomy and help in surgical planning. 

• Transposition procedures: New surgical techniques are being developed to correct complex strabismus.

Living with Strabismus  

Impact on Quality of Life 

Untreated strabismus can have a significant impact on daily life in a number of ways, including:

• Vision problems: Strabismus can cause double vision and blurred vision, which can make doing daily activities and completing school work challenging. 

• Psychosocial and emotional problems: Strabismus can cause problems such as low self-esteem, social anxiety, and relationship difficulties. Adults and children with strabismus may experience prejudice, bullying, and loss of job opportunities. 

• Risk of injuries: People with strabismus are at an increased risk of injuries and accidents due to vision problems. 

• Irreversible vision loss: Untreated strabismus can increase the risk of irreversible vision loss.

Long-Term Effects and Prognosis

Strabismus surgery has a high success rate and is considered a safe procedure. The long-term effects and prognosis (outcomes) from strabismus treatment depend on the age at which the condition is treated, the type of strabismus, and the complexity of the surgery. 

Children treated early for strabismus typically have an excellent outcome. Eye muscle surgery is also more successful in young children. If left untreated, amblyopia (lazy eye) can lead to permanent vision loss in one eye. Response to treatment is minimal after age 8, when the visual system has fully matured.

Coping Strategies and Support Groups  

• Tips on living with strabismus

• Vision therapy success stories

Common Questions and Concerns  

Is Strabismus Considered a Visual Disability?  

Strabismus isn't usually considered a disability unless it significantly affects daily functions and leads to reduced quality of life.

How to Find a Treatment Center?

Your primary care provider can refer you to an ophthalmologist (eye doctor) or strabismologist (specialist in strabismus diagnosis and treatment). 

How to Prevent Strabismus?

You cannot prevent strabismus, but you can improve outcomes by seeking treatment early for any eye symptoms. It’s also important to get regular eye checkups to monitor eye health in children and adults.