Crossed Eyes (Squint)

WHAT IS IT?

Crossed-eyes, also called squint or strabismus, occurs when the eyes appear to be misaligned and point in different directions. Strabismus can occur at any age, but is most common in infants and young children.

Strabismus can occur part of the time (intermittent) or all of the time (constant). Intermittent strabismus may worsen when the eye muscles are tired -- late in the day, for example, or during the course of an illness. Parents may notice their infant's eyes wandering from time to time during the first few months of life, especially when the infant is tired. This occurs because the infants are still learning to focus their eyes and to move them in a coordinated fashion. Most babies outgrow this intermittent strabismus by the age of 3 months.

Strabismus may be caused by problems with the eye muscles, with the nerves that control the eye muscles or with the brain where the signals for vision are processed. Strabismus can accompany some systemic illnesses like diabetes, high blood pressure, multiple sclerosis, myasthenia gravis or thyroid disorders.

Strabismus is classified according to the direction of misalignment. When one eye is looking straight ahead, the other eye may turn inward toward the nose (esotropia or convergent), outward toward the ear (exotropia or divergent), downward (hypotropia), or upward (hypertropia).

Esotropia is the most common type of strabismus.

Infantile esotropia is present at birth or develops within the first six months of life. The child often has a family history of strabismus.

Many infants appear to have strabismus but do not. Rather, they have a condition known as pseudostrabismus (or pseudoesotropia), in which a widened nasal bridge or an extra fold of skin makes the white sclera less visible on the nose side of the eye. This gives the appearance that the eyes are crossed. This usually resolves as the infant grows and the facial structures change.

Accommodative esotropia is seen in children who are very farsighted. Their eyes cross because of difficulty focusing on nearby objects. Parents notice the child's eyes intermittently turning in, usually when he or she is concentrating on something up close. Accommodative esotropia is typically diagnosed between ages 2 and 3 years. A family history of this condition is common.

Strabismus has mistakenly been called lazy eye or amblyopia, which refers to diminished vision in one or both otherwise anatomically normal eyes. However, strabismus can lead to amblyopia. When the eyes are not aligned, the brain receives two different images, resulting in double vision. In young children the visual system has not reached full maturity and the brain is able to suppress the image from one eye to avoid double vision. Amblyopia results if vision from one eye is consistently suppressed and the other eye becomes dominant. If a lazy eye is uncorrected by the age of 9 years, the functional capacity of that eye remains permanently poor.

Symptoms of strabismus include:

1.    Eyes that look misaligned 2.    Eyes that do not appear to move together 3.    Frequent blinking or squinting, especially in bright sunlight 4.    Tilting head to look at things 5.    Faulty depth perception 6.    Double vision 7.    Poor vision in one or both eyes

DIAGNOSIS

The evaluation for suspected strabismus usually includes a medical and visual history and a test for visual acuity (how well one sees with each eye). The diagnosis of strabismus is best made with a careful eye exam. The examiner evaluates the alignment of the eyes, looking for evidence of uncoordinated eye movements. In infants and young children with limited ability to cooperate, comparing the position of a light reflecting off each eye usually assesses alignment. However, this test may not detect intermittent strabismus unless it is present at the time of testing. In patients who are able to cooperate, both intermittent and constant strabismus can be detected using the cover-uncover and alternating cover tests. To perform these tests, the patient stares at an object and the examiner watches the response of each of the patient's eyes when the other is covered and uncovered.

EXPECTED DURATION

The intermittent strabismus seen in infants is associated with normal development and typically resolves before 3 months of age. Other types of strabismus do not resolve unless treated.

PREVENTION

Children should be monitored closely during infancy and the preschool years to detect potential eye problems, particularly if a relative has strabismus. Early detection, accurate diagnosis, and proper treatment can cure strabismus. It is recommended that all children be screened for eye health before age 6 months and again between 3 and 5 years of age by a pediatrician or an ophthalmologist.

Routine vision screening for young children includes testing for strabismus, usually using the light reflex for infants, and cover testing for preschool-age children.

TREATMENT

The primary goal of treatment is to preserve or restore as much visual function as possible. Treatments vary, depending on the type and cause of strabismus. Glasses are used to correct vision in the weaker eye. Patches are worn over the preferred eye to force the use of the weaker or suppressed eye. Eye drops are used to temporarily blur the vision of the preferred eye. Exercises may be prescribed to strengthen specific eye muscles.

Forcing a child to use the weaker eye can improve sight by reinforcing the connection between the eye and the brain.

Surgery to tighten or loosen specific eye muscles is usually required to realign the eyes. This operation is typically done under general anesthesia and may involve one or both eyes. Occasionally alignment is not achieved with the first surgery and additional surgery is needed.

Any concerns about a child's ability to see or about the alignment of his or her eyes should be raised with your ophthalmologist as soon as possible. Constant strabismus at any age or intermittent strabismus that persists beyond 3 months of age usually needs prompt referral to an ophthalmologist.

Adults who develop double vision or other signs of strabismus should contact their ophthalmologist for further evaluation.

PROGNOSIS

With early detection, accurate diagnosis and proper treatment, the prognosis with strabismus is excellent. Treatment before age 8-9 years and especially by 6 years of age gives the best results.