Definition

Strabismus, commonly known as crossed eyes, occurs when the eyes are not aligned and look in different directions. One eye may look straight ahead while the other turns inward, outward, upward, or downward. This condition typically affects babies and children, particularly around the age of three, but can also occur in adults.

The eyes can move because muscles control them. There are six eye muscles that control eye movement. One muscle moves the eye to the right while the other one moves it to the left. Four more muscles move the eyeballs up, down, and around each corner. To focus on a single image, all six eye muscles need to work together.

Both eyes must be pointed at the same place to see properly. Therefore, strabismus conditions will result in vision problems. A healthy eye alignment during childhood will result in good vision development. However, amblyopia is a condition that can arise if the eyes are misaligned for an extended period of time. Amblyopia is a condition in which the misaligned eye is weaker and experiences impaired vision compared to the aligned eye.

Causes

All eye muscles must work together to focus both eyes on a single point. Strabismus can arise from issues with the eye muscles, the nerves controlling these muscles, or the brain areas that coordinate eye movement. Consequently, children with strabismus might also have associated brain disorders, such as:

• Cerebral palsy (impaired body movement and coordination)
• Down syndrome
• Hydrocephalus (fluid accumulation in the brain)
• Brain tumors
• Premature birth

Cataracts (cloudy lenses) and eye injuries can also lead to strabismus. In adults, strabismus is often associated with other conditions affecting eye muscles, such as:

• Diabetes
• Thyroid disease
• Myasthenia gravis
• Brain tumors
• Stroke
• Head injuries or traumas
• Eye muscle damage after eye surgery

Risk Factor

Several factors increasing the risk of strabismus include:

• Family history. Individuals with parents or siblings who have strabismus are more likely to develop the condition.
• Refractive disorders. Uncorrected or untreated hyperopia (farsightedness) can lead to strabismus.

Symptoms

In normal vision, both eyes focus on the same point, enabling the brain to merge the two images from each eye into a single, three-dimensional image. This integration allows us to perceive the distance of objects accurately.

When the eyes are not properly aligned, the brain receives two disparate images, initially causing double vision for the affected individuals. Over time, the brain may adapt by ignoring the image from the misaligned eye. If left untreated, this misalignment can weaken the affected eye, resulting in amblyopia, commonly known as lazy eye.

Signs of strabismus in children include the eyes pointing in different directions simultaneously, the inability of both eyes to move together, the child closing one eye or tilting the head when focusing on an object, squinting one eye in bright sunlight, and poor perception of three-dimensional image.

Strabismus can be classified based on the direction of the misalignment:

• Esotropia: the eyes turn inward (toward the nose)
• Exotropia: the eyes turn outward (away from the nose)
• Hypertropia: the eyes turn upward
• Hypotropia: the eyes turn downward

In adults, the signs and symptoms of strabismus are similar to those in children. The most prominent sign is misaligned eyes. Other symptoms include:

• A sensation of something pulling around the eyes
• Visual disturbances, such as double vision, blurred vision, reading difficulty, or loss of three-dimensional image perception
• Frequent tilting or turning of the head to see properly

A condition similar to strabismus is pseudostrabismus, or false crossed eyes, where a child's eyes appear crossed despite being properly aligned. This condition often occurs in children under one year old, particularly if they have a broad, flat nose or folds of skin on the inner eyelids. The appearance of crossed eyes typically diminishes as the child's facial structure develops.

To distinguish strabismus from pseudostrabismus, a light can be shone into the child's eyes. If the reflection of light is centered on both pupils, the child has pseudostrabismus. If the reflection is off-center in one eye, the child has strabismus. Children with pseudostrabismus have normal vision, unlike those with strabismus

Diagnosis

An ophthalmologist diagnoses strabismus with various examinations:

• Patient medical history: The doctor will inquire about the patient's symptoms, other related medical issues, medications taken by patients, and potential risk factors.
• Visual acuity: The doctor measures how much the vision is impaired.
• Refraction: The appropriate lens to correct refractive errors is determined.
• Alignment and focus tests: The doctor assesses how well the eyes focus, move, and work together.
• Comprehensive eye condition test: This includes checking the eye from the outside to the inside to rule out other related eye problems.

Management

The doctor may recommend one or more types of strabismus treatments based on the child's age and eye alignment. For infants and very young children with esotropia, treatment options include surgery or corrective glasses. Surgical intervention on the eye muscles can help align the eyes, thereby enhancing vision.

Children over two years old with esotropia are typically prescribed special glasses designed to help focus and straighten the eyes. In some cases, prism lenses are utilized to aid in focusing to see. A prism, a clear wedge-shaped lens, refracts light rays. Prisms can be attached to glasses or integrated into the lens. A prism with a thicker side refracts light in a manner that prevents the eye from misaligning when focusing on an object.

To strengthen the misaligned, weaker eye, covering or obscuring the stronger eye might be recommended. This can be achieved with an eye patch or by using eye drops to blur the vision in the stronger eye, thereby forcing the use of the weaker eye and gradually strengthening it.

Children may also be taught specific eye muscle exercises to improve the coordination of both eyes. If glasses, prisms, eye patches, or exercises are insufficient, surgery may be considered.

Strabismus Surgery

Surgery aims to correct the alignment of the child's eyes. Under general anesthesia, a small incision is made in the tissue covering the eye to access the eye muscles. These muscles are then repositioned to align the eyes. This procedure can be done to one or both eyes, and in some cases, a second surgery may be required. After the surgery, most children can resume their activities within a few days.

Strabismus surgery is a safe and effective method for treating eye misalignment. However, it does not replace other treatments, such as glasses or eye patches, if also recommended by the doctor. Multiple types of eye care can be combined to strengthen the eye muscles and maintain proper alignment. In adults, treatment for strabismus is similar to that in children, involving eye muscle exercises, prism glasses, and surgery.

Complications

Untreated strabismus can lead to amblyopia, where the misaligned eye becomes weaker and experiences vision loss.

Prevention

Strabismus itself cannot be prevented, but complications can be avoided with early detection. Children should undergo eye health screenings at a minimum age of 6 months and again at 3-5 years.

When to See a Doctor?

Consult an ophthalmologist for a complete eye examination if you notice signs and symptoms of strabismus in your child or family. Early diagnosis and treatment are crucial for preventing complications and ensuring proper vision development.

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