(Squint; Cross-Eye; Wandering Eye)
Strabismus is an intermittent or constant misalignment of an eye so that its line of vision is not pointed at the same object as the other eye. If untreated, strabismus can cause amblyopia (a decrease in vision) and permanent loss of vision. Treatment of strabismus includes correction of any refractive error, a patch or eye drops to treat amblyopia, and in some cases surgery.
Strabismus is misalignment of the eyes.
Causes include focusing (refractive) error and imbalance of muscles that control eye movement.
Symptoms include double vision and loss of vision.
The diagnosis is based on an eye examination.
Strabismus sometimes resolves on its own, but in most cases eyeglasses, contact lenses, or surgery is needed.
Strabismus occurs in about 3% of children. It may appear in the first few months of life or later in childhood, depending on the cause. If left untreated, about 50% of children with strabismus have some vision loss due to amblyopia.
Most strabismus is caused by a refractive error (nearsightedness, farsightedness, or astigmatism) or an imbalance in the pull of muscles that control the position of the eyes. Severe vision loss in one eye (due to refractive error or less common disorders such as cataracts) can cause strabismus because it interferes with the brain’s ability to maintain the alignment of the eyes.
Less common causes include paralysis or weakness of one of the cranial nerves that control eye movement (the 3rd, 4th, or 6th nerve), which impairs the ability to move the eyes and keep them aligned properly (see Palsies of Cranial Nerves That Control Eye Movement) and retinoblastoma (a type of eye cancer). Sometimes a fracture of the eye socket can block movement of the eye and cause strabismus.
There are several types of strabismus. Some types are characterized by inward turning of the eye (esotropia or cross-eye) and some by outward turning of the eye (exotropia or walleye). Other types are characterized by upward turning of the eye (hypertropia) or downward turning of the eye (hypotropia). The defect in alignment may be constant or intermittent and may be mild or severe.
A phoria is an unseen, minor misalignment of the eyes. This misalignment is easily corrected by the brain to maintain apparent alignment of the eyes and allow fusion of the images from both eyes. Thus, phorias usually do not cause symptoms and do not need treatment unless they are large and decompensate, causing double vision (diplopia).
A tropia is a constant, visible deviation or misalignment of one eye or both eyes. An intermittent eye deviation that is frequent and poorly controlled by the brain is termed intermittent tropia.
Parents sometimes notice strabismus because the child squints or covers one eye. The defect may be detected by observing that the child's eyes appear to be positioned abnormally or do not move in unison. Unless severe, phorias rarely cause symptoms. If symptomatic, phorias typically cause eye strain. Tropias sometimes cause symptoms. Younger children frequently lose vision in one eye (amblyopia) because their brain suppresses the image from the misaligned eye to avoid confusion and double vision. Older children may have double vision or they may have twisting or spasm of the neck (torticollis) to compensate for the misaligned eyes.
Children should be examined periodically to measure vision and to detect strabismus starting at a few months of age. To examine an infant, a doctor shines a light into the eyes to see whether the light reflects back from the same location on each pupil.
Older children can be examined more thoroughly. Children may be asked to recognize objects or letters with one eye covered and to participate in tests to assess alignment of the eyes. All children with strabismus require examination by an eye doctor (ophthalmologist).
Doctors may do imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI—see Imaging Tests), of the brain or spinal cord in children with cranial nerve palsies.
Strabismus should not be ignored or watched on the assumption that it will be outgrown. Permanent vision loss can occur if amblyopia occurs and is not treated before age 4 to 6 years. Children treated at a later age can improve with treatment, but once the visual system has matured (typically by age 8), response to treatment is minimal. As a result, all children should have formal vision screening in the preschool years.
Success rates with surgical repair of strabismus can be greater than 80%.
If the defect is minor or intermittent, treatment may not be needed. However, if strabismus is severe or is progressing, treatment is required.
Treatment depends on the characteristics and cause of the strabismus. Treatment aims to equalize vision and then align the eyes. For children with amblyopia, doctors "handicap" the normal, stronger eye by putting a patch over it or using eye drops to blur its vision. Patching is not, however, a treatment for strabismus. For children with significant focusing error, doctors usually prescribe eyeglasses or contact lenses. Sometimes eye exercises can help correct intermittent exotropia.
To treat strabismus, the eyes are aligned surgically when nonsurgical methods are unsuccessful in aligning the eyes satisfactorily. Surgical repair consists of loosening (recession) and tightening (resection) of the eye muscles. Children usually are not hospitalized for this surgical procedure. However, the procedure can cause complications, the most common of which are correction beyond what is needed (overcorrection) or correction below what is needed (undercorrection) and strabismus that recurs later in life. Rarely, children may develop an infection, excessive bleeding, or vision loss.