Background

Exotropia is a type of strabismus, commonly known as “wall-eyed” or “wandering eye,” characterized by the outward deviation of one eye while the other eye maintains a straight-ahead position. It is the opposite of esotropia, where one eye turns inward. Exotropia can occur intermittently or persistently, and it can affect one or both eyes.

Epidemiology

The epidemiology of exotropia, or the prevalence and distribution of the condition in the population, can vary depending on various factors such as geographical location, age groups studied, and diagnostic criteria used. Here are some general observations regarding the epidemiology of exotropia:

• Prevalence: Exotropia is one of the most common types of strabismus. The reported prevalence rates can range widely, from 0.6% to 4.5% of the population, depending on the study population and diagnostic criteria.
• Age of onset: Exotropia often develops in childhood, typically between the ages of 2 and 4 years, although it can manifest at any age. In some cases, it may present in infancy or early childhood and persist into adulthood.
• Gender differences: Some studies have reported a slightly higher prevalence of exotropia in females, while others have not found a significant gender difference. The exact relationship between gender and exotropia remains unclear and requires further investigation.
• Ethnic and racial differences: There is limited data on the potential variations in exotropia prevalence among different ethnic or racial groups. Studies conducted in specific populations have reported varying rates of exotropia, but no consistent patterns have been observed.
• Association with refractive errors: Exotropia has been found to be more common in individuals with high hyperopia (farsightedness) or astigmatism. The presence of refractive errors can contribute to the development or progression of exotropia.
• Association with other conditions: Exotropia may be associated with certain neurological disorders, such as cerebral palsy, Down syndrome, or developmental delay. It can also occur as a result of trauma or acquired conditions affecting the eye muscles or nerves.

Anatomy

Pathophysiology

The pathophysiology of exotropia involves an imbalance or dysfunction of the extraocular muscles responsible for eye movement and alignment. Several factors contribute to the development of exotropia, including muscular abnormalities, sensory disturbances, and neural control issues. Here are some key aspects of the pathophysiology of exotropia:

• Muscular Imbalance: Exotropia is often associated with a disparity in the strength or coordination of the extraocular muscles that control eye movement. The condition may occur due to weakness or underaction of the medial rectus muscle, which is responsible for inward eye movement, or overaction of the lateral rectus muscle, which causes outward eye movement.
• Sensory Factors: The coordination between the eyes relies on sensory input from both eyes, which is processed in the brain. In exotropia, there may be a disruption in the sensory fusion mechanism that helps maintain binocular vision. Binocular vision allows the brain to fuse the images from both eyes into a single, three-dimensional perception. Sensory disturbances can affect the ability to perceive depth and contribute to the misalignment of the eyes.
• Abnormal Neural Control: The control of eye movements is regulated by a complex interplay between the ocular motor cranial nerves, brainstem nuclei, and higher-level neural centers. Dysfunction in these neural pathways can disrupt the coordination of eye movements and lead to exotropia. Issues with the integration of visual information, motor commands, or the neural feedback loops involved in eye alignment can contribute to the pathophysiology of the condition.
• Accommodative Factors: Accommodation refers to the ability of the eyes to focus on near objects by adjusting the shape of the lens. Excessive accommodative effort or accommodative insufficiency can be associated with exotropia. When the eyes struggle to maintain clear and single vision during near work, such as reading or focusing on close objects, the strain can lead to the deviation of one eye.
• Anatomic Abnormalities: Structural abnormalities or anomalies in the anatomy of the eye muscles, nerves, or surrounding tissues can contribute to the development of exotropia. These abnormalities may affect the normal functioning and alignment of the eye muscles, leading to the outward deviation of one eye.

Etiology

The etiology, or underlying causes, of exotropia can vary and may involve a combination of genetic, environmental, and anatomical factors. While the exact cause of exotropia is not always known, several factors have been identified as potential contributors. Here are some common etiological factors associated with exotropia:

• Genetics: There is evidence to suggest a genetic predisposition to exotropia. Family history and the presence of exotropia in close relatives can increase the risk of developing the condition. However, the specific genes involved and the mode of inheritance are not well understood and require further research.
• Refractive Errors: Refractive errors, such as hyperopia (farsightedness), astigmatism, or anisometropia (significant difference in refractive error between the two eyes), are commonly associated with exotropia. These visual abnormalities can create an imbalance in the focusing of light on the retina, leading to eye strain and misalignment.
• Sensory Factors: Disorders or disruptions in binocular vision and sensory fusion mechanisms can contribute to exotropia. Sensory factors involve the coordination of visual information from both eyes to create a single, three-dimensional image. Any impairment in this process can lead to misalignment of the eyes.
• Muscle Imbalance and Weakness: Exotropia can occur due to a muscular imbalance or weakness in the extraocular muscles that control eye movement. Weakness or underaction of the medial rectus muscle (responsible for inward eye movement) or overaction of the lateral rectus muscle (causing outward eye movement) can result in the deviation of the eye.
• Neurological Disorders: Certain neurological conditions, such as cerebral palsy, Down syndrome, hydrocephalus, or brain tumors, can be associated with exotropia. These conditions may affect the neurological control of eye movements or result in muscle weakness, leading to misalignment.
• Trauma or Injury: Exotropia can develop as a result of trauma or injury to the eye muscles or nerves involved in eye movement. Damage to the muscles or disruption of the neural pathways that control eye alignment can cause the outward deviation of the eye.

Genetics

Prognostic Factors

The prognosis of exotropia can vary depending on several factors, including the severity of the condition, age of onset, underlying causes, and treatment interventions. Here are some considerations regarding the prognosis of exotropia:

• Early Detection and Intervention: Early detection and timely intervention can have a positive impact on the prognosis of exotropia. Prompt diagnosis and appropriate treatment during childhood can potentially improve eye alignment, promote binocular vision development, and minimize the risk of long-term complications.
• Severity of Exotropia: The severity of the exotropia can influence the prognosis. Mild or intermittent exotropia may have a better prognosis compared to constant and larger deviations. Mild cases of exotropia often have a higher likelihood of responding to non-surgical interventions, such as corrective lenses, vision therapy, or prism glasses.
• Compliance with Treatment: Patient compliance with prescribed treatments, such as wearing corrective lenses, patching, or engaging in vision therapy exercises, can significantly impact the prognosis. Consistent adherence to treatment recommendations can improve eye alignment, strengthen eye muscles, and enhance binocular vision.
• Underlying Causes and Associated Conditions: Exotropia associated with refractive errors, convergence insufficiency, or certain neurological conditions may have a more favorable prognosis when the underlying causes are appropriately addressed. Treatment of associated conditions, such as correcting refractive errors or managing convergence insufficiency, can contribute to better outcomes.
• Surgical Intervention: Eye muscle surgery is often considered for cases of persistent or cosmetically significant exotropia. The prognosis following surgery can be favorable, with improved eye alignment and cosmesis. However, it is important to note that the extent of correction and the long-term stability of the surgical outcomes can vary among individuals.
• Long-Term Follow-up: Regular and long-term follow-up is crucial to monitor the progression of exotropia, assess treatment outcomes, and address any potential complications or recurrences. Ongoing evaluation allows for appropriate adjustments in treatment if needed.

Clinical History

Clinical history

When taking a clinical history of a patient with exotropia, healthcare professionals should gather relevant information to understand the characteristics, progression, and impact of the condition. Here are some key elements to consider when obtaining a clinical history of a patient with exotropia:

• Onset and Duration: Inquire about the age at which the exotropia was first noticed and whether it has been present since childhood or developed later in life. Determine if the deviation is constant or intermittent, and if there have been any changes in the frequency or severity of the exotropia over time.
• Symptoms: Ask about any accompanying symptoms or complaints associated with the exotropia. Common symptoms include double vision (diplopia), difficulty with depth perception, eye strain, eye fatigue, or headaches, especially after prolonged visual tasks or in certain gaze positions.
• Visual Function: Assess the patient’s visual acuity, both with and without corrective lenses, to identify any refractive errors or visual impairments. Determine if there is a history of wearing glasses or contact lenses. Inquire about any difficulty with near vision tasks, such as reading or focusing on close objects.
• Family History: Determine if there is a family history of strabismus or any other eye conditions, as there may be a genetic component to exotropia. Ask about the presence of strabismus, amblyopia (lazy eye), or other eye disorders in parents, siblings, or other close relatives.
• Previous Treatments: Inquire about any prior treatments or interventions for exotropia. Ask if the patient has undergone patching, vision therapy, prescription eyeglasses, or eye muscle surgery in the past. It is important to understand the effectiveness and outcomes of previous interventions.
• Impact on Daily Life: Assess how exotropia affects the patient’s daily activities, including school, work, sports, and social interactions. Inquire about any difficulties with eye contact, self-esteem, or psychological well-being due to the appearance or functional impact of the exotropia.
• Medical History: Obtain a comprehensive medical history to identify any underlying conditions or factors that may contribute to exotropia. Inquire about any history of neurological disorders, developmental delay, trauma to the eyes or head, or any other significant medical conditions.
• Medications: Ask about any current medications the patient is taking, as certain medications can have ocular side effects or contribute to eye muscle dysfunction.

Physical Examination

Physical examination

During the physical examination of a patient with exotropia, healthcare professionals assess various aspects of eye alignment, visual function, and associated findings. Here are key components of the physical examination for exotropia:

• Visual Acuity: Measure visual acuity in each eye using an eye chart, both with and without corrective lenses if applicable. This helps identify any refractive errors or visual impairments that may contribute to or accompany the exotropia.
• Cover-Uncover Test: Perform the cover-uncover test to assess the deviation and presence of any latent or intermittent exotropia. Covering one eye and then quickly uncovering it can reveal the presence and magnitude of the eye deviation.
• Alternate Cover Test: Use the alternate cover test to measure the degree of eye deviation. By covering and uncovering each eye alternately, the examiner can determine the magnitude and direction of the exotropia in different gaze positions.
• Ocular Motility Evaluation: Assess the range of eye movements, including horizontal, vertical, and torsional (rotational) movements. Observe for any limitations, restrictions, or abnormalities in eye movements, especially in adduction and abduction.
• Stereopsis and Binocular Vision: Evaluate the patient’s ability to perceive depth and appreciate stereoscopic vision using tests such as the Titmus or Randot stereopsis tests. Assess binocular vision and fusion ability to determine if the patient has developed suppression (ignoring one eye) or anomalous retinal correspondence (misalignment of corresponding retinal points).
• Near Point of Convergence: Evaluate the near point of convergence (NPC) to assess the patient’s ability to maintain binocular vision while focusing on a near target. The examiner observes for any convergence insufficiency, which can be associated with exotropia.
• Fundus Examination: Perform a fundus examination to assess the health of the optic nerve, retina, and other ocular structures. This helps identify any associated abnormalities or potential causes of the exotropia.
• General Examination: Conduct a general examination, including assessment of facial symmetry, cranial nerve function, and any signs of underlying neurological or systemic disorders that may be associated with exotropia.
• Cycloplegic Refraction: In some cases, cycloplegic refraction may be performed to accurately assess refractive errors, especially in younger patients who may have accommodative factors contributing to the exotropia.

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

Differential diagnosis

When evaluating a patient with exotropia, it is important to consider other conditions that can cause similar signs or symptoms. The following are some of the differential diagnoses that may be considered when assessing a case of exotropia:

• Divergence Insufficiency: Divergence insufficiency is a condition characterized by an outward deviation of the eyes that is more pronounced at distance fixation. Unlike exotropia, divergence insufficiency is typically not present at near fixation and may be associated with age-related changes in the ability to maintain eye alignment.
• Duane Syndrome: Duane syndrome is a congenital eye movement disorder characterized by limited horizontal eye movement, particularly inward gaze, due to abnormal innervation of the extraocular muscles. It can sometimes present with an exotropic appearance, but the limitation of eye movement and associated features can help differentiate it from primary exotropia.
• Sensory Exotropia: Sensory exotropia can occur in the presence of significant visual impairment in one eye, resulting in an outward deviation of the eye. This deviation is an adaptive response to reduce diplopia (double vision) caused by the visual impairment. It is important to identify and address the underlying cause of sensory impairment in these cases.
• Monocular Elevation Deficiency (Double Elevator Palsy): Monocular elevation deficiency is a congenital disorder characterized by limited elevation of one eye in adduction and elevation. This condition may present with an exotropic appearance due to the affected eye appearing lower than the fellow eye. Limitation of eye movement and associated features can aid in distinguishing it from primary exotropia.
• Cranial Nerve Palsy: Cranial nerve palsies, particularly involving the sixth cranial nerve (abducens nerve), can result in an outward deviation of the eye. However, in cranial nerve palsies, there is usually limited eye movement in the direction controlled by the affected muscle, along with associated neurological signs.
• Brown Syndrome: Brown syndrome is a limited elevation of the eye in adduction due to a mechanical restriction of the superior oblique muscle. It can sometimes present with an exotropic appearance but is characterized by limited elevation of the eye, particularly in adduction.
• Convergence Insufficiency: Convergence insufficiency is a common binocular vision disorder characterized by difficulty converging the eyes when looking at near objects. While convergence insufficiency primarily affects near vision, it can occasionally present with exotropia.

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

The treatment of exotropia aims to improve eye alignment, promote binocular vision, and address any associated visual impairments. The appropriate treatment approach depends on factors such as the severity of the exotropia, age of the patient, presence of underlying conditions, and individual patient preferences. Here are some common treatment options for exotropia:

• Observation and Monitoring: In cases of mild, intermittent exotropia, observation and periodic monitoring may be appropriate, especially if the deviation is not causing significant symptoms or functional limitations. Regular follow-up visits allow the healthcare provider to assess the stability of the condition and intervene if needed.
• Correction of Refractive Errors: Addressing any underlying refractive errors, such as hyperopia (farsightedness), astigmatism, or anisometropia (unequal refractive error between the two eyes), is an important step in the management of exotropia. Prescription eyeglasses or contact lenses can help optimize visual acuity and potentially improve eye alignment.
• Patching and Vision Therapy: For patients with certain types of exotropia, particularly those with accommodative factors or convergence insufficiency, patching the dominant eye or engaging in vision therapy exercises may be beneficial. These interventions can help strengthen eye muscles, improve convergence ability, and enhance binocular vision.
• Prism Glasses: Prism glasses can be prescribed to help reduce the deviation and improve binocular vision. The prismatic effect of the glasses shifts the visual image, allowing the eyes to align more naturally. Prism glasses are often used in cases of small to moderate exotropia or as a temporary measure before considering surgical intervention.
• Botulinum Toxin Injection: In some cases, botulinum toxin (Botox) injections may be used to treat exotropia, particularly in patients who are not suitable candidates for surgery or who prefer a temporary solution. The toxin weakens the overacting muscles responsible for the exotropic deviation, helping to realign the eyes temporarily.
• Surgical Intervention: Eye muscle surgery, also known as strabismus surgery, may be considered for patients with persistent or cosmetically bothersome exotropia. The surgical procedure involves adjusting the tension and positioning of the eye muscles to align the eyes properly. Surgery can improve eye alignment, enhance binocular vision, and address associated visual symptoms. However, it is important to note that surgery may not fully restore normal eye movement or eliminate the need for corrective lenses.

The choice of treatment depends on the specific needs and characteristics of each patient. The healthcare provider will consider factors such as the severity of the exotropia, presence of refractive errors or convergence insufficiency, patient age, and individual goals when formulating a treatment plan. A multidisciplinary approach involving ophthalmologists, optometrists, and orthoptists is often employed to provide comprehensive care and maximize treatment outcomes.

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

Medication

Future Trends

Media Gallary

References

https://www.ncbi.nlm.nih.gov/books/NBK578185/