Exotropia refers to a type of strabismus where the eye(s) turn outward. The outward turn may occur constantly or once in a while and affect one or both eyes. It is the opposite of esotropia where the eyes turn inward. Some children can develop infantile exotropia before six months of life. Those with this type may continue to be affected by exotropia beyond that period. Exotropia affects eyesight when the child loses the three-dimensional vision or depth perception. In some newborns, the eyes may straighten on their own by the time they reach two or three months old. Exotropia is not as common among newborns as esotropia.
Exotropia affecting children may be classified into:
- Primary infantile exotropia where it develops without eye or systemic diseases. This condition may be an autosomal inheritance disorder or may develop sporadically
- Secondary infantile exotropia which is caused by certain ocular disorders such as cataract, ptosis, nystagmus, retinoblastoma, albinism, and other strabismus disorders such as Duane syndrome. Systemic diseases like cerebral palsy and craniofacial syndrome can lead to this type of esotropia
Others classify exotropia as:
- Congenital exotropia where it is present at birth
- Acquired exotropia where exotropia develops secondary to other factors. Subcategories of this type include sensory exotropia (poor vision in the affected eye and which begins in children over five years), consecutive exotropia (which develops after eye muscle surgery), and intermittent exotropia
Exotropia can also be classified as:
- Constant, which in infants could be an indication of other medical conditions such as cerebral palsy. In constant exotropia, the eyes are misaligned throughout. Congenital esotropia is also classified as constant
- Intermittent, where the eyes are aligned one time and not at other times. It is easily noticeable when the child is daydreaming, tired, or looking into the distance. This type begins in children around the age of two
Causes & Risk Factors
Exotropia appears to be a hereditary disease that runs in families even though the family members may not have similar types or share in disease severity. It is also believed that a disorder involving a 3rd cranial nerve palsy is responsible. Previous strabismus or eye muscle surgery may cause exotropia. The cause of intermittent childhood exotropia remains unknown. There are no known risk factors for childhood exotropia. However, pediatric cataracts, pediatric glaucoma, genetic disorders of the eye, and family history of childhood cataracts and amblyopia should encourage further investigation.
Signs & Symptoms
Signs and symptoms may include:
- Double vision
- Rubbing one of the eyes
- Blurry or decreased vision
- Squinting in bright sunlight
- A reduced depth of perception
- Outward turning of the eye when the child is ill, tired, or daydreaming in intermittent exotropia
The following methods can be used to diagnose exotropia:
- Genetic testing
- Retinal examination
- Visual acuity test to check a child’s vision
- An age-appropriate comprehensive eye exam
- Slit lamp examination to check for signs of strabismus
- Cycloplegic refraction using dilating eye drops to check for refractive errors
- Family and patient medical history to check for signs like strabismus, cataract, amblyopia, etc.
- Imaging tests such as MRI to check if nerves and not muscles cause the eye alignment problems
- During well-baby clinics, the child can be screened for eye alignment where exotropia can be diagnosed early
- Physical examination where a baby’s fixation preferences are examined, for example, if the baby prefers to look with one eye
- Strabismus evaluation using specific tests such as alternate prism cover test, passive forced duction tests, etc. In uncooperative infants, the Krimsky test is used
Treatment is aimed at correcting the misalignment and improving vision.
Eyeglasses can correct refractive errors such as astigmatism, hyperopia (farsightedness), and myopia (nearsightedness). In case of amblyopia or lazy eye, the better-seeing eye can be patched to improve vision in the weaker eye. Should a child have a small angle of exotropia, prisms can assist in relieving double vision. However, prisms do not treat the misalignment of the eye.
Surgery can be performed on the eye muscles to aid in realigning the eyes. However, surgery is recommended with constant exotropia. The patient has significant symptoms such as squinting, double vision, or eye strain. Surgery is also indicated in patients showing evidence of losing binocular vision (the two eyes focusing on a single object simultaneously). If glasses or other methods can control exotropia, there is no need for surgery.
Eye exercises can help improve vision in the weaker eye.
Prognosis & Long-Term Outlook
With proper treatment, children with exotropia enjoy excellent vision.
Prevention & Follow Up
While it is not possible to prevent congenital exotropia, other types can be controlled. Children need to get the recommended hours of sleep and keep healthy. Sickness in a child can cause temporary, intermittent exotropia. Such children need to see an ophthalmologist frequently to ensure the visual system is good. If not, appropriate glasses can be used to fine-tune the optical system.