Exotropia refers to a type of strabismus in which one eye or both of them deviate outwards. It may be constant or intermittent and congenital or acquired. Early detection and treatment of the condition is important in improving vision and preventing complications.
Constant outward drift of the eye in children below 12 months is the most characteristic feature of infantile or congenital exotropia. Craniofacial syndromes may also be seen along with exotropia in most of these cases. After a period of time this may develop into fixation with one eye while the other eye which develops amblyopia. More than half of the patients with congenital exotropia may develop dysfunction of oblique muscles.
In acquired exotropia, patient may complain of eye strain after a prolonged session involving visual work. Some patients may develop diplopia. There are instances where the patient proactively tries to control exodeviation and feels that objects appear closer and smaller. Some patients, particularly children, tend to close one of the eyes in bright light. This usually precedes the actual manifestation of outward drifting of eye. It is considered that closing of one eye helps to avoid diplopia and a confusion in vision. People with intermittent exotropia may also complain of asthenopia, blurred vision, difficulty in reading, and head ache. When left without treatment, intermittent exotropia may deteriorate or remain the same.
Patients with consecutive exotropia may have constant unilateral exotropia while focusing on both distant and near objects. They have high levels of stereopsis and the ability for binocular vision reduces considerably. Diplopia is also common among these patients. Mechanical exotropia is characterized by increased deviation of vision axes. These patients may turn their head as a compensatory habit. Patients with sensory exotropia may show high degrees of anisometropia and also show frequent vertical deviations along with the outward shifts.
A thorough examination and evaluation of eye and vision are the most important steps in the diagnosis of this condition. When needed, a more detailed evaluation of sensory, motor and refractive functions can be included. Detailed patient history with details of nature of onset, frequency of deviation, family history of strabismus, presence of diplopia or any other vision problems, will help in gathering information about the general eye condition. Assessing the health of the eye would help to check for congenital abnormalities and other coexisting conditions.
Visual acuity should be measured for each of the eye to check for the presence of amblyopia. Visual acuity cards help in quantifying the problem in children. For adults, psychometric acuity cards are recommended. Unilateral test when the patient fixes on an object, either placed far or near, helps to establish the frequency and extend of deviation. Prism cover test enables to evaluate the magnitude of vision deviation. For young children, corneal reflex test is preferred. As refractive error is one of the most important cause for developing this condition, it should be accurately measured to decide on the line of treatment. And this measurement should be done in both cycloplegic and non-cycloplegic conditions.
Neurologic defects and craniofacial abnormalities can be detected using imaging studies in congenital exotropia. If any other systemic abnormalities are present, chromosomal studies may be suggested.
Treatment modality for exotropia aims at obtaining normal visual acuity in each eye, improving the alignment of eye and improving fusion. The course of therapy will depend on factors like age of the patient at onset, frequency and size of deviation, or the presence or absence of amblyopia.
For patients who have a good control of deviation, any of the non-surgical measures may be used for optical correction. This will also avoid the risk of surgical overcorrection. Correction of refractive errors like astigmatism and anisometropia will increase fusional ability and help in improving exotropia. Minus lenses are found to be helpful in controlling divergence, particularly in children in the age group of 2-17 years . Progression of exotropia can be limited by patching of the eye, either dominant or alternate, depending on whether the condition is unilateral. This helps to prevent the process of suppression. Small comitant deviations may be controlled by base-in-prisms. Near point of convergence is improved by convergence exercises and this particularly is true for patients who have convergence insufficiency. Botulinum toxin injections are found to be effective in treating secondary exotropia. In patients with bitemporal visual defects, prisms are recommended to avoid diplopia.
Surgery is suggested for those patients who have very poor control of deviation and in those where exotropia is deteriorating. Surgery is also recommended for those who have diplopia and severe asthenopia. Lateral rectus muscle recession, ipsilateral medial rectus muscle resection and bilateral medial rectus muscle resection are some of the surgical measures used for improving different types of exotropia.
Congenital exotropia, if detected and treated early, would help in restoring binocular vision. Even if amblyopia develops, vision can be resolved during the early stages of disease progression. Outcome of acquired exotropia, on the other hand, depends on several factors. Surgical correction of the misalignment before four years of age may help in preventing amblyopia. But care should be taken not to have overcorrection. Surgery may also aid in increased fusional control of vision. It is important to continue treatment of refractive error for better results. Postoperative care should include improvement of motor alignment and sensory functions to resolve the problem completely.
The actual biological cause of this condition is not yet fully understood. Structural abnormalities of the muscles are considered to be one of the causes for the misalignment.
Exotropia is classified into different types:
Exotropic anomalies are less common when compared to esotropia, in the ratio of 1:3 . Exotropia is found to be more prevalent among Middle East and subequatorial African population. Latitudes with higher amount of sunlight is reported to have more incidence of this ocular misalignment disorder . About 40% of the cases with exotropia develop this disorder before the second year of their life . It is noted that children who are born with craniofacial abnormalities have an increased risk of developing exotropia. It is also more common among people with neurologic defects. Information on prevalence of this condition among adults is very less. Intermittent exotropia, which often go unnoticed, is the most common form of this condition and is found to affect about 1% of the population . The prevalence of this condition is more among women when compared to men.
Presence of multiple conditions like cerebral palsy, Down’s syndrome and craniofacial dysostosis increases the risk of developing this condition. Premature children are also at a higher risk of exotropia when compared to children born full-term.
Exodeviations are found to run in families and a multifactorial genetic basis is attributed to this . Prevalence of ocular misalignment is found to be more frequent in children whose parents or siblings have this condition. In most of the cases the eyes are aligned straight when open, but shift outward when one is closed. It may later develop into intermittent exotropia. And if the eyes and vision are still developing when this occurs, it may lead to diplopia due to bitemporal suppression. The patient may not be able to perceive two separate images, particularly while focusing on a distant object. One of the eyes may be fixed on the object and the other one may drift outwards. This is a progressive condition and intermittent exotropia leads to constant exotropia. In most of the cases, misalignment of the eye develops in childhood. Metabolic diseases may lead to the development of this condition in adulthood. It may also develop due to decompensation of heterophoria.
Most of the cases of exotropia cannot be prevented, but early detection and correction of the condition may go a long way in improving vision and preventing progression of the condition. Children who are suspected to have exodeviations should be examined as early as possible. Starting the treatment early enough would help in achieving normal binocular vision.
Exotropia, or divergent strabismus, is an ocular misalignment disorder in which one or both eyes deviate outward from normal. Exotropia is more frequent in females than in men and when present, it may be constant or intermittent. If the condition presents itself in the first few months of life, it is categorized as congenital exotropia, and when developing after six months it is referred to as acquired exotropia. Acquired exotropia may be intermittent, acute or mechanical. Exotropia may result from a sensory deficit or as a side effect of a treatment, and this type falls under the category of secondary exotropia. This misalignment disorder may be accompanied by other visual anomalies including double vision, poor vision or a change in the motility of the eye. Early identification and treatment of the condition in children may prevent further complications in vision like amblyopia . If left untreated, these ocular changes may become permanent.
Exotropia refers to a misalignment condition in which one eye or both of tem drift outwards. It may be constant or intermittent and congenital or acquired. It is found in all age groups. Presence of this condition from birth or early stages of infancy is referred to as congenital or infantile exotropia. Acquired exotropia refers to outward deviation that develops after six months of age. The actual cause of the disorder is not known yet. It is suggested that defects of the muscles that control eye movements, or nerve anomalies, lead to exotropia. Some conditions like nerve disorders, thyroid problems, and trauma may all result in exotropia.
The first signs of this condition is mostly seen during childhood. The outward drift of the eye is noticeable when the child is daydreaming or focusing on a distant object. Observing these symptoms is important as most of the children with this condition consider that double vision and nearsightedness are normal. Some of the common symptoms of this condition in children include covering one eye to improve vision, excessive rubbing of eyes, closing of eyes in bright light, squint and double vision. These symptoms if left untreated may lead to constant exotropia and other complications.
In most of the cases, parents are the first ones to notice changes in vision and alignment of the eyes in children. In those who develop it at a later stage, a regular visit to the physician may reveal the presence of this disorder. A thorough eye examination is suggested to find the underlying cause and extent of problem. For mild cases of this condition, eye lenses and exercises are suggested. Both of these help in controlling deviation of the eye. Temporary eye patches are suggested for those who have decreased vision in one of the eyes. Surgical methods are used if the symptoms are severe and if there is an increase in the frequency of deviations.