Exotropia

Last updated
Exotropia
Other namesDivergent squint, wall eyes
David Prowse 2013.jpg
David Prowse displaying exotropia of both eyes
Specialty Ophthalmology

Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia and usually involves more severe axis deviation than exophoria. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision in one eye. Infantile exotropia (sometimes called "congenital exotropia") is seen during the first year of life, and is less common than "essential exotropia" which usually becomes apparent several years later.

Contents

The brain's ability to see three-dimensional objects depends on proper alignment of the eyes. When both eyes are properly aligned and aimed at the same target, the visual portion of the brain fuses the two forms from the two eyes into a single image. When one eye turns inward, outward, upward, or downward, two different pictures are sent to the brain. Thus, the brain can no longer fuse the two images coming from the two eyes. This causes loss of depth perception and binocular vision. The term is from Greek exo meaning "outward" and trope meaning "a turning". [1]

Signs and symptoms

Denzel Washington is one of a number of celebrities with exotropia Denzel Washington cropped 02.jpg
Denzel Washington is one of a number of celebrities with exotropia

The earliest sign of exotropia is usually a noticeable outward deviation of the eye. This sign may at first be intermittent, occurring when a child is daydreaming, not feeling well, or tired. It may also be more noticeable when the child looks at something in the distance. Squinting or frequent rubbing of the eyes is also common with exotropia. The child probably will not mention seeing double, i.e., double vision or diplopia. However, he or she may close one eye to compensate for the problem. In children, the reason for not seeing double is that the brain may ignore the image it receives from the squinting eye. This shutting down is known as 'suppression'.

Generally, exotropia progresses in frequency and duration. As the disorder progresses, the eyes start to turn out when looking at close objects as well as those in the distance. If left untreated, the eye may turn out continually, causing a loss of binocular vision or stereopsis.

In young children with any form of strabismus, the brain may learn to ignore the misaligned eye's image and see only the image from the best-seeing eye. This is called amblyopia, or lazy eye, and results in a loss of binocular vision, impairing depth perception. In adults who develop strabismus, double vision sometimes occurs because the brain has already been trained to receive images from both eyes and cannot ignore the image from the turned eye.

Additionally in adults who have had exotropia since childhood, the brain may adapt to using a "blind-spot", whereby it receives images from both eyes, but no full image from the deviating eye, thus avoiding double vision, and in fact, increasing peripheral vision on the side of the deviating eye.

According to a study published in the American Journal of Ophthalmology, over 90 percent of children with intermittent exotropia become nearsighted by the time they reach 20. [2]

Causes

The causes of exotropia are not fully understood. Six muscles control eye movement, four that move the eye up and down and two that move it left and right. All these muscles must be coordinated and working properly for the brain to see a single image. When one or more of these muscles does not work properly, some form of strabismus may occur. Strabismus is more common in children with disorders that affect the brain such as cerebral palsy, Down syndrome, hydrocephalus, and brain tumors. One study has found that children with exotropia are three times more likely to develop a psychiatric disorder in comparison with the general population. [3] [4] [5]

Treatment

A comprehensive eye examination including an ocular motility (i.e., eye movement) evaluation and an evaluation of the internal ocular structures allows an eye doctor to accurately diagnose exotropia. Although glasses and/or patching therapy, exercises, or prisms may reduce or help control the outward-turning eye in some children, surgery is often required.

A common form of exotropia is known as "convergence insufficiency" that responds well to orthoptic vision therapy including exercises. This disorder is characterized by an inability of the eyes to work together when used for near viewing, such as reading. Instead of the eyes focusing together on the near object, one deviates outward.

Consecutive exotropia arises after an initial esotropia. Most often it results from surgical overcorrection of the initial esotropia. It can be addressed with further surgery or with vision therapy; vision therapy has shown promising results if the consecutive exotropia is intermittent, alternating, and of small magnitude. [6] (Consecutive exotropia may however also spontaneously develop from esotropia, without surgery or botulinum toxin treatment. [7] )

Because of the risks of surgery, and because about 35% of people require at least one more surgery, many people try vision therapy first. This consists of visual exercises. Although vision therapy is generally not covered by American health insurance companies, many large insurers such as Aetna [8] have recently begun offering full or partial coverage in response to recent studies.

Strabismus surgery is sometimes recommended if the exotropia is present for more than half of each day or if the frequency is increasing over time. It is also indicated if a child has significant exotropia when reading or viewing near objects or if evidence shows that the eyes are losing their ability to work as a single unit (binocular vision). Finally, if there is a complaint of headaches, and no other cause for the headaches can be found, then these headaches could be because the child or adult is trying to control the exotropia. If none of these criteria are met, surgery may be postponed pending simple observation with or without some form of eyeglass and/or patching therapy. In very mild cases, a chance exists that the exotropia will diminish with time. The long-term success of surgical treatment for conditions such as intermittent exotropia is not well proven, and surgery can often result in a worsening of symptoms due to overcorrection. Evidence from systematic reviews of interventions show clinical benefits for patching for children ages 12 months to ten years. [9] There was insufficient evidence related to the benefits conferred by surgical interventions. [9]

The surgical procedure for the correction of exotropia involves making a small incision in the tissue covering the eye to reach the eye muscles. The appropriate muscles are then repositioned to allow the eye to move properly. The procedure is usually done under general anaesthesia. Recovery time is rapid, and most people are able to resume normal activities within a few days. Following surgery, corrective eyeglasses may be needed, and in many cases, further surgery is required later to keep the eyes straight.

When a child requires surgery, the procedure is usually performed before the child attains school age. This is easier for the child and gives the eyes a better chance to work together. As with all surgery, some risks occur. However, strabismus surgery is usually a safe and effective treatment.

Related Research Articles

<span class="mw-page-title-main">Esotropia</span> Form of strabismus

Esotropia is a form of strabismus in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. It is the opposite of exotropia and usually involves more severe axis deviation than esophoria. Esotropia is sometimes erroneously called "lazy eye", which describes the condition of amblyopia; a reduction in vision of one or both eyes that is not the result of any pathology of the eye and cannot be resolved by the use of corrective lenses. Amblyopia can, however, arise as a result of esotropia occurring in childhood: In order to relieve symptoms of diplopia or double vision, the child's brain will ignore or "suppress" the image from the esotropic eye, which when allowed to continue untreated will lead to the development of amblyopia. Treatment options for esotropia include glasses to correct refractive errors, the use of prisms, orthoptic exercises, or eye muscle surgery. The term is from Greek eso meaning "inward" and trope meaning "a turning".

<span class="mw-page-title-main">Binocular vision</span> Type of vision with two eyes facing the same direction

In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an animal has eyes on opposite sides of its head and shares no field of view between them, like in some animals.

Orthoptics is a profession allied to the eye care profession. Orthoptists are the experts in diagnosing and treating defects in eye movements and problems with how the eyes work together, called binocular vision. These can be caused by issues with the muscles around the eyes or defects in the nerves enabling the brain to communicate with the eyes. Orthoptists are responsible for the diagnosis and non-surgical management of strabismus (cross-eyed), amblyopia and eye movement disorders. The word orthoptics comes from the Greek words ὀρθός orthos, "straight" and ὀπτικός optikοs, "relating to sight" and much of the practice of orthoptists concerns disorders of binocular vision and defects of eye movement. Orthoptists are trained professionals who specialize in orthoptic treatment, such as eye patches, eye exercises, prisms or glasses. They commonly work with paediatric patients and also adult patients with neurological conditions such as stroke, brain tumours or multiple sclerosis. With specific training, in some countries orthoptists may be involved in monitoring of some forms of eye disease, such as glaucoma, cataract screening and diabetic retinopathy.

<span class="mw-page-title-main">Strabismus</span> Eyes not aligning when looking at something

Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is pointed at an object can alternate. The condition may be present occasionally or constantly. If present during a large part of childhood, it may result in amblyopia, or lazy eyes, and loss of depth perception. If onset is during adulthood, it is more likely to result in double vision.

<span class="mw-page-title-main">Amblyopia</span> Failure of the brain to process input from one eye

Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amblyopia is the most common cause of decreased vision in a single eye among children and younger adults.

Anisometropia is a condition in which a person's eyes have substantially differing refractive power. Generally, a difference in power of one diopter (1D) is the threshold for diagnosis of the condition. Patients may have up to 3D of anisometropia before the condition becomes clinically significant due to headache, eye strain, double vision or photophobia.

<span class="mw-page-title-main">Diplopia</span> Double vision

Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results in impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. Problems with these muscles may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves that innervate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.

Vision therapy (VT), or behavioral optometry, is an umbrella term for alternative medicine treatments using eye exercises, based around the pseudoscientific claim that vision problems are the true underlying cause of learning difficulties, particularly in children. Vision therapy has not been shown to be effective using scientific studies, except for helping with convergence insufficiency. Most claims—for example that the therapy can address neurological, educational, and spatial difficulties—lack supporting evidence. Neither the American Academy of Pediatrics nor the American Academy of Ophthalmology support the use of vision therapy.

<span class="mw-page-title-main">Vergence</span> Simultaneous movement of eyes in binocular vision

A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision.

<span class="mw-page-title-main">Sixth nerve palsy</span> Medical condition

Sixth nerve palsy, or abducens nerve palsy, is a disorder associated with dysfunction of cranial nerve VI, which is responsible for causing contraction of the lateral rectus muscle to abduct the eye. The inability of an eye to turn outward, results in a convergent strabismus or esotropia of which the primary symptom is diplopia in which the two images appear side-by-side. Thus, the diplopia is horizontal and worse in the distance. Diplopia is also increased on looking to the affected side and is partly caused by overaction of the medial rectus on the unaffected side as it tries to provide the extra innervation to the affected lateral rectus. These two muscles are synergists or "yoke muscles" as both attempt to move the eye over to the left or right. The condition is commonly unilateral but can also occur bilaterally.

Suppression of an eye is a subconscious adaptation by a person's brain to eliminate the symptoms of disorders of binocular vision such as strabismus, convergence insufficiency and aniseikonia. The brain can eliminate double vision by ignoring all or part of the image of one of the eyes. The area of a person's visual field that is suppressed is called the suppression scotoma. Suppression can lead to amblyopia.

<span class="mw-page-title-main">Hypertropia</span> Condition of misalignment of the eyes

Hypertropia is a condition of misalignment of the eyes (strabismus), whereby the visual axis of one eye is higher than the fellow fixating eye. Hypotropia is the similar condition, focus being on the eye with the visual axis lower than the fellow fixating eye. Dissociated vertical deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive.

<span class="mw-page-title-main">Strabismus surgery</span> Surgery to correct strabismus

Strabismus surgery is surgery on the extraocular muscles to correct strabismus, the misalignment of the eyes. Strabismus surgery is a one-day procedure that is usually performed under general anesthesia most commonly by either a neuro- or pediatric ophthalmologist. The patient spends only a few hours in the hospital with minimal preoperative preparation. After surgery, the patient should expect soreness and redness but is generally free to return home.

Infantile esotropia is an ocular condition of early onset in which one or either eye turns inward. It is a specific sub-type of esotropia and has been a subject of much debate amongst ophthalmologists with regard to its naming, diagnostic features, and treatment.

Dissociated vertical deviation (DVD) is an eye condition which occurs in association with a squint, typically infantile esotropia. The exact cause is unknown, although it is logical to assume it is from faulty innervation of eye muscles.

<span class="mw-page-title-main">Stereopsis recovery</span>

Stereopsis recovery, also recovery from stereoblindness, is the phenomenon of a stereoblind person gaining partial or full ability of stereo vision (stereopsis).

Botulinum toxin therapy of strabismus is a medical technique used sometimes in the management of strabismus, in which botulinum toxin is injected into selected extraocular muscles in order to reduce the misalignment of the eyes. The injection of the toxin to treat strabismus, reported upon in 1981, is considered to be the first ever use of botulinum toxin for therapeutic purposes. Today, the injection of botulinum toxin into the muscles that surround the eyes is one of the available options in the management of strabismus. Other options for strabismus management are vision therapy and occlusion therapy, corrective glasses and prism glasses, and strabismus surgery.

Bagolini striated glasses test, or BSGT, is a subjective clinical test to detect the presence or extent of binocular functions and is generally performed by an optometrist or orthoptist or ophthalmologist. It is mainly used in strabismus clinics. Through this test, suppression, microtropia, diplopia and manifest deviations can be noted. However this test should always be used in conjunction with other clinical tests, such as Worth 4 dot test, Cover test, Prism cover test and Maddox rod to come to a diagnosis.

<span class="mw-page-title-main">Muscle imbalance</span> Medical condition

Muscle balance is necessary for muscles to perform their customary roles and move normally; muscle imbalance occurs when there is a lack of parity between corresponding agonist and antagonist muscles. Muscular imbalance can also arise when a muscle performs outside of its normal physiological muscle function.

The management of strabismus may include the use of drugs or surgery to correct the strabismus. Agents used include paralytic agents such as botox used on extraocular muscles, topical autonomic nervous system agents to alter the refractive index in the eyes, and agents that act in the central nervous system to correct amblyopia.

References

  1. ↑ "Exotropia Origin". dictionary.com . Retrieved 21 July 2015.
  2. ↑ Ekdawi, Noha S.; Nusz, Kevin J.; Diehl, Nancy N.; Mohney, Brian G. (2010). "The Development of Myopia Among Children with Intermittent Exotropia". American Journal of Ophthalmology. 149 (3): 503–507. doi:10.1016/j.ajo.2009.10.009. PMC   3926435 . PMID   20172074.
  3. ↑ Mohney BG, McKenzie JA, Capo JA, Nusz KJ, Mrazek D, Diehl NN (November 2008). "Mental illness in young adults who had strabismus as children". Pediatrics . 122 (5): 1033–8. doi:10.1542/peds.2007-3484. PMC   2762944 . PMID   18977984.
  4. ↑ Mayo Clinic. "Eye Divergence In Children Triples Risk Of Mental Illness." ScienceDaily 28 November 2008. 30 November 2008
  5. ↑ McKenzie J, et al "Prevalence and sex differences of psychiatric disorders in young adults who had intermittent exotropia as children" Arch Ophthalmol 2009; 127:743-47.
  6. ↑ B. Chorn; A. Steiner. "Optometric Vision Therapy in the Management of Consecutive Intermittent Exotropia with Dissociated Vertical Deviation and Anomalous Correspondence - A Case Study". Journal of Behavioral Optometry (JBO). Vol. 18, no. 6. (abstract Archived 2014-09-07 at the Wayback Machine , full text Archived 2014-09-07 at the Wayback Machine )
  7. ↑ J.D. Senior; A. Chandna; A.R. O'Connor (2009). "Spontaneous consecutive exotropia in childhood". Strabismus. 17 (1): 33–6. doi:10.1080/09273970802678818. PMID   19301191. S2CID   7513855.
  8. ↑ Clinical policy bulletins: Vision therapy, Number 0489, 4 June 2013, for review 13 June 2013 (downloaded 21 July 2013)
  9. 1 2 Pang, Yi; Gnanaraj, Lawrence; Gayleard, Jessica; Han, Genie; Hatt, Sarah R. (2021-09-13). "Interventions for intermittent exotropia". The Cochrane Database of Systematic Reviews. 2021 (9): CD003737. doi:10.1002/14651858.CD003737.pub4. ISSN   1469-493X. PMC   8437222 . PMID   34516656.
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