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For the similar condition, where the eyes deviate inward (rather than outward), see esotropia.

Exotropia (from Greek εξοτρὀπια, εξο "exo" meaning "to exit" or "move out of" and τρὀπειν "tropein" meaning "to turn") is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision. 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.

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 forms into a single image. When one eye turns inward, outward, upward, or downward, two different pictures are sent to the brain. This causes loss of depth perception and binocular vision.

Causes

The causes of exotropia are not fully understood. There are six muscles that control eye movement, four that move the eye up and down and two that move it side to side. All these muscles must be coordinated and working properly in order for the brain to see a single image. When one or more of these muscles doesn't 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.^[1]^[2]^[3]

Signs and symptoms

Queen Elizabeth II's granddaughter Lady Louise Windsor was born with esotropia.^[4]^[5]

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. However, he or she may close one eye to compensate for the problem.

Generally, exotropia progresses in frequency and duration. As the disorder progresses, the eyes will 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.

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.

Treatment

A comprehensive eye examination including an ocular motility (eye movement) evaluation and an evaluation of the internal ocular structures will allow an eye doctor to accurately diagnose the 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.

There is a common form of exotropia 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 (exotropia resulting from surgical overcorrection of an initial esotropia) 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]

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^[7] have recently begun offering full or partial coverage in response to recent studies.

Surgery is sometimes recommended if the exotropia is present for more than half of each day or if the frequency is increasing over time. Surgery is also indicated if a child has significant exotropia when reading or viewing near objects or if there is evidence that the eyes are losing their ability to work as a single unit (binocular vision). 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, there is a chance 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.

The surgical procedure for the correction of exotropia involves making a small incision in the tissue covering the eye in order to reach the eye muscles. The appropriate muscles are then repositioned in order to allow the eye to move properly. The procedure is usually done under general anesthesia. 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, there are some risks. However, strabismus surgery is usually a safe and effective treatment.

References

Notes

^ 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.
^ Mayo Clinic. "Eye Divergence In Children Triples Risk Of Mental Illness." ScienceDaily 28 November 2008. 30 November 2008
^ 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.[1]
^ English, Rebecca; Knight, Kathryn (10 July 2007). "How Sophie's become the Queen's favourite". Daily Mail. Retrieved 15 October 2011.
^ Elizabeth Sanderson (13 February 2011). "Sophie’s little Lady Louise picked as royal bridesmaid". Daily Mail. Retrieved 15 October 2011.
^ 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) 18 (6). (abstract, full text)
^ Clinical policy bulletins: Vision therapy, Number 0489, 4 June 2013, for review 13 June 2013 (downloaded 21 July 2013)

UpToDate Contents

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1. 小児における水平斜視の原因 causes of horizontal strabismus in children
2. 小児における斜視の評価およびマネージメント evaluation and management of strabismus in children
3. 複視の概要 overview of diplopia
4. 小児における第3脳神経（動眼神経）麻痺 third cranial nerve oculomotor nerve palsy in children
5. 視覚変化が認められた小児患者に対するアプローチ approach to the pediatric patient with vision change

English Journal

Squinting and photophobia in intermittent exotropia.

Oh BL1, Suh SY, Choung HK, Kim SJ.Author information 1*MD Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Republic of Korea (all authors); and Seoul Artificial Eye Center, Seoul National University Hospital Clinical Research Institute, Seoul, Republic of Korea (all authors).AbstractPURPOSE: To report factors associated with preoperative squinting, defined as transient eye closure in bright light, and photophobia and the factors affecting improvement of these symptoms postoperatively in intermittent exotropia.
Optometry and vision science : official publication of the American Academy of Optometry.Optom Vis Sci.2014 May;91(5):533-9. doi: 10.1097/OPX.0000000000000251.
PURPOSE: To report factors associated with preoperative squinting, defined as transient eye closure in bright light, and photophobia and the factors affecting improvement of these symptoms postoperatively in intermittent exotropia.METHODS: In this retrospective study, patients (N = 99) were divided
PMID 24727823

Visual function and compensatory mechanisms for hemianopia after hemispherectomy in children.

Koenraads Y1, van der Linden DC, van Schooneveld MM, Imhof SM, Gosselaar PH, Porro GL, Braun KP.Author information 1Department of Ophthalmology, University Medical Center Utrecht, Utrecht, The Netherlands.AbstractOBJECTIVE: Little is known about the functional visual outcome of children after hemispherectomy. Several case reports have described an anomalous head posture (AHP) and exotropia (XT) contralateral to the side of early brain damage, as possible compensatory mechanisms (CMs) for homonymous hemianopia (HH). The aim of this study was to determine visual outcome and the prevalence of such CMs in hemispherectomized children.
Epilepsia.Epilepsia.2014 Apr 22. doi: 10.1111/epi.12615. [Epub ahead of print]
OBJECTIVE: Little is known about the functional visual outcome of children after hemispherectomy. Several case reports have described an anomalous head posture (AHP) and exotropia (XT) contralateral to the side of early brain damage, as possible compensatory mechanisms (CMs) for homonymous hemianopi
PMID 24754334

Age-related distance esotropia - fusional amplitudes and clinical course.

Oatts JT1, Salchow DJ.Author information 1Yale University School of Medicine, Department of Ophthalmology and Visual Science , New Haven , United States and.AbstractAbstract Background: Age-related distance esotropia (ARDET) is a form of acquired strabismus that affects elderly patients and manifests as an esotropia greater with distance fixation. Limited information exists regarding fusional amplitudes and deficient divergence in this disorder. Methods: In this retrospective study, patient characteristics, ocular alignment and motility, and clinical course of patients with ARDET were recorded. Fusional amplitudes were analyzed to assess whether deficient divergence was present in patients with ARDET. Results: Twenty patients with ARDET were identified. Median age was 77.5 years (range, 59 to 89 years) and median best-corrected visual acuity was 20/25. Median esotropia angle with distance fixation was 5.5Δ (range, 2 to 18Δ); median angle with near fixation was esotropia 2.5Δ (range, exotropia 3Δ to esotropia 13Δ). Fusional divergence amplitudes were decreased in all but two patients. The median amplitude with distance fixation was 4.5Δ for break (range, 1 to 11Δ) and 2Δ for recovery (range, 0 to 9Δ). In 5 patients, the fusional divergence amplitude was as large or larger than the esotropia angle. Most patients remained stable throughout a mean follow-up of 18 months (range, 3 to 37 months). Nineteen patients were managed with prisms. Strabismus surgery was performed in one patient. Conclusions: Fusional divergence amplitude was deficient in most but not all patients with ARDET. In this study, most patients with ARDET remained stable and free of diplopia with prism treatment.
Strabismus.Strabismus.2014 Apr 22. [Epub ahead of print]
Abstract Background: Age-related distance esotropia (ARDET) is a form of acquired strabismus that affects elderly patients and manifests as an esotropia greater with distance fixation. Limited information exists regarding fusional amplitudes and deficient divergence in this disorder. Methods: In thi
PMID 24754801