Background

Esotropia is a type of strabismus, commonly known as “crossed eyes,” characterized by the inward deviation of one or both eyes. In esotropia, one eye may turn inward towards the nose, while the other eye maintains a straight or relatively normal alignment. This misalignment can be intermittent or constant and can occur in varying degrees of severity.

Epidemiology

Esotropia is a relatively common form of strabismus, particularly in childhood. The epidemiology of esotropia can vary depending on factors such as age, geographic location, and specific subtypes of esotropia. Here are some key points regarding the epidemiology of esotropia:

• Prevalence: Esotropia is estimated to occur in approximately 1-2% of the general population. It is one of the most prevalent types of strabismus.
• Age of Onset: Esotropia often develops during early childhood, with a peak onset between 1 and 4 years of age. However, it can occur at any age, including infancy (infantile esotropia) and adulthood (acquired or secondary esotropia).
• Sex Distribution: Esotropia appears to affect both males and females equally, without a significant gender predominance.
• Ethnic and Geographic Variations: The prevalence of esotropia may vary among different ethnic and geographic populations. Some studies have suggested higher rates of esotropia in populations of Asian descent, while others have reported similar rates across different ethnic groups.
• Subtypes of Esotropia: Esotropia can be classified into various subtypes, each with its own epidemiological characteristics. For example, infantile esotropia is more commonly observed in early infancy, while accommodative esotropia is often associated with hyperopia (farsightedness) and typically presents in older children.
• Association with Refractive Errors: Esotropia is frequently associated with refractive errors, particularly hyperopia (farsightedness). Uncorrected hyperopia can contribute to the development or worsening of esotropia.
• Family History: There is a higher prevalence of esotropia in individuals with a family history of strabismus. The genetic component and inheritance patterns of esotropia are still being studied.
• Amblyopia: Esotropia can lead to amblyopia (lazy eye), which is a significant visual impairment in the affected eye. Amblyopia is more likely to occur when esotropia develops at an earlier age and is left untreated.

Anatomy

Pathophysiology

The pathophysiology of esotropia, a form of strabismus characterized by inward deviation of one or both eyes, involves an imbalance in the control and coordination of the extraocular muscles responsible for eye movements. This imbalance disrupts the normal alignment and coordination between the eyes, leading to the characteristic crossed appearance of esotropia. Here are the key components of the pathophysiology of esotropia:

• Extraocular Muscle Imbalance: Esotropia results from an imbalance in the functioning of the extraocular muscles, which control the movements of the eyes. The two primary muscles involved in esotropia are the medial rectus muscle, responsible for inward eye movement (adduction), and the lateral rectus muscle, responsible for outward eye movement (abduction). In esotropia, the medial rectus muscles are either overactive or stronger relative to the lateral rectus muscles, causing the eye(s) to turn inward.
• Fusional Control and Binocular Vision: The normal alignment and coordination of the eyes are necessary for binocular vision, which provides depth perception and optimal visual processing. In individuals with esotropia, there is a disruption in the fusional control, which is the ability of the eyes to maintain binocular alignment. The brain attempts to compensate for the misalignment by suppressing or ignoring the input from the deviated eye, leading to reduced binocular vision and potentially resulting in amblyopia (lazy eye) in the affected eye.
• Accommodation and Refractive Errors: Esotropia can be associated with refractive errors, particularly hyperopia (farsightedness). Uncorrected hyperopia can cause the eyes to excessively accommodate (focus) in an attempt to clear the blurred vision, leading to increased convergence (inward turning) of the eyes. This accommodative component of esotropia can be improved or even resolved by providing appropriate corrective lenses to address the refractive error.
• Nerve and Brain Dysfunction: In some cases, esotropia may result from abnormalities in the nerves or brain structures that control eye movements. This can include conditions such as cranial nerve palsies or abnormalities in the oculomotor pathways. These neurological factors can disrupt the normal communication and coordination between the brain and the extraocular muscles, leading to esotropia.

The underlying cause of the muscle imbalance and disruption in eye coordination in esotropia is not always well understood. While certain genetic factors and family history can contribute to the development of esotropia, the specific mechanisms and genetic components are still being studied. Understanding the pathophysiology of esotropia is essential for appropriate diagnosis and management.

Treatment approaches aim to correct the misalignment, promote binocular vision, and address any underlying refractive errors or associated conditions. These may include glasses or contact lenses, patching or blurring the stronger eye to encourage visual development in the weaker eye, vision therapy exercises, and, in some cases, surgical correction to realign the eyes and restore binocular vision.

Etiology

The etiology of esotropia, a form of strabismus characterized by inward deviation of one or both eyes, can vary depending on the subtype and individual case. The underlying causes of esotropia are multifactorial and can involve a combination of genetic, anatomical, neurological, and environmental factors. Here are some common etiological factors associated with esotropia:

• Genetics: Esotropia can have a hereditary component, with a higher prevalence observed in individuals with a family history of strabismus. Specific genes and inheritance patterns contributing to esotropia are still being studied.
• Refractive Errors: Uncorrected refractive errors, particularly hyperopia (farsightedness), can contribute to the development of esotropia. Hyperopia may lead to excessive accommodative effort to focus on near objects, resulting in increased convergence (inward turning) of the eyes.
• Muscle Imbalance: Esotropia can occur due to an imbalance in the extraocular muscles responsible for eye movements. The medial rectus muscle, responsible for inward eye movement (adduction), may be overactive or stronger compared to the lateral rectus muscle, leading to the inward deviation of the eye(s).
• Nerve and Brain Abnormalities: Some cases of esotropia may be associated with underlying neurological conditions or abnormalities affecting the nerves or brain structures involved in eye movement control. This can include cranial nerve palsies, brainstem lesions, or abnormalities in the oculomotor pathways.
• Developmental Factors: Esotropia can arise during the developmental period, with specific subtypes having distinct etiological factors. Infantile esotropia, which presents in early infancy, is believed to be primarily related to abnormal development of the extraocular muscles or their neural control.
• Systemic Conditions: Esotropia can be associated with certain systemic conditions or syndromes, including genetic disorders, metabolic diseases, and neurological disorders. Examples include Down syndrome, cerebral palsy, and Moebius syndrome.
• Environmental Factors: Some environmental factors may contribute to the development or worsening of esotropia. These factors can include visual stimuli, such as excessive near work or prolonged use of digital devices, as well as environmental stressors that affect visual development.

Genetics

Prognostic Factors

The prognosis of esotropia depends on various factors, including the type and severity of esotropia, the underlying cause, the age at which it is diagnosed and treated, and the response to treatment. Here are some key considerations regarding the prognosis of esotropia:

• Early Detection and Treatment: Early detection and intervention are associated with better outcomes, particularly in cases of infantile esotropia. Prompt treatment can help prevent or minimize the development of amblyopia (lazy eye) and facilitate the development of binocular vision.
• Severity of Esotropia: The severity of the esotropia may influence the prognosis. Large-angle or constant esotropia may require more aggressive treatment approaches, such as surgery, and may have a longer recovery period compared to smaller-angle or intermittent deviations.
• Underlying Cause: The underlying cause of esotropia can impact the prognosis. For example, esotropia caused by refractive errors, such as hyperopia, can often be effectively managed with glasses or contact lenses, resulting in good alignment and visual outcomes. On the other hand, esotropia associated with neurological conditions or cranial nerve palsies may have a more guarded prognosis.
• Amblyopia: The presence of amblyopia can affect the prognosis of esotropia. Amblyopia occurs when the brain favors one eye over the other due to an imbalance in vision. Early detection and treatment of amblyopia, such as through patching or atropine therapy, can help improve visual acuity and enhance the overall prognosis.
• Compliance with Treatment: The patient’s and caregivers’ compliance with the recommended treatment plan, including the use of glasses, patching, or vision therapy, is crucial for achieving optimal outcomes. Consistent follow-up visits and adherence to the prescribed treatment regimen are important for monitoring progress and making necessary adjustments.
• Associated Conditions: Esotropia can be associated with other ocular or systemic conditions that may impact the prognosis. Conditions such as genetic syndromes, craniofacial abnormalities, or neurologic disorders can present additional challenges and may require a multidisciplinary approach for management.
• Individual Variability: Each individual’s response to treatment can vary. Some individuals may achieve complete resolution of esotropia and develop normal binocular vision, while others may have residual alignment issues or require ongoing management to maintain alignment and visual function.

Clinical History

Clinical History

When obtaining the clinical history of a patient with esotropia, it is important to gather relevant information that can help in understanding the onset, progression, and characteristics of the condition. Here are some key components to consider when taking the clinical history of a patient with esotropia:

• Onset and Duration: Determine when the esotropia was first noticed or reported by the patient or caregiver. Establish whether the esotropia has been present since birth (infantile esotropia) or if it developed later in life (acquired esotropia). Note the duration of the deviation and whether it is constant or intermittent.
• Age of Presentation: Determine the age at which the esotropia was first observed or reported. Note any specific triggering events, such as illness or trauma, around the time of onset.
• Family History: Inquire about a family history of strabismus or any other eye conditions. Esotropia can have a genetic component, and a positive family history may increase the likelihood of a hereditary influence.
• Symptoms: Ask about any accompanying symptoms or visual complaints associated with esotropia. Common symptoms include diplopia (double vision), eye strain, blurred vision, or difficulty with depth perception. In children, they may have difficulty with reading, focusing, or participating in activities requiring binocular vision.
• Visual Acuity: Assess the patient’s visual acuity in each eye individually to determine if there is any significant difference between the eyes. Note if there is any history of decreased vision in either eye (amblyopia or lazy eye).
• Refractive Error: Determine if the patient has any known refractive errors, such as hyperopia (farsightedness), myopia (near-sightedness), or astigmatism. Refractive errors can contribute to the development or worsening of esotropia and may require correction with glasses or contact lenses.
• Previous Treatments: Inquire about any previous treatments or interventions for the esotropia, including the use of glasses, patching, vision therapy, or prior surgical procedures. Note the response to previous treatments and any changes in the condition.
• Developmental Milestones: Obtain information about the patient’s developmental milestones, including motor skills and milestones related to vision, such as eye contact, tracking objects, and reaching for objects.
• Social and Academic Impact: Assess the impact of the esotropia on the patient’s daily activities, social interactions, and academic performance. Note any self-esteem issues or challenges faced due to the misalignment of the eyes.
• Associated Conditions: Inquire about any known or suspected associated conditions, such as neurological disorders, genetic syndromes, or previous ocular trauma, as these can influence the etiology and management of esotropia.

Physical Examination

Physical examination

When conducting a physical examination of a patient with esotropia, the focus is on assessing the alignment and movement of the eyes, evaluating visual function, and identifying any associated ocular or systemic abnormalities. Here are the key components of the physical examination for esotropia:

• Visual Acuity: Test the visual acuity of each eye individually using appropriate methods based on the patient’s age and cooperation. Evaluate both distance and near vision. Note any significant difference in visual acuity between the eyes, which may indicate amblyopia (lazy eye).
• Ocular Alignment: Assess the alignment of the eyes in different gaze positions, including primary gaze, distant fixation, and near fixation. Observe for any deviation of one or both eyes inward (esotropia) and note whether the deviation is constant or intermittent.
• Ocular Motility: Evaluate the range of eye movements in all directions of gaze. Observe for limitations in specific directions of movement or any associated nystagmus (involuntary eye movements). Assess abduction (outward eye movement) and note any restriction or abnormality.
• Cover-Uncover Test: Perform the cover-uncover test to assess for latent (intermittent) deviations. Cover one eye and observe the movement of the uncovered eye. Repeat the test for each eye to assess for any latent esotropia or exotropia.
• Alternate Prism Cover Test: Use prism lenses to perform the alternate prism cover test. This test helps determine the angle of deviation and assesses the presence of binocular fusion. It is used to measure the magnitude and direction of the deviation and can be useful in planning surgical correction if needed.
• Near Point of Convergence: Assess the near point of convergence, which is the distance at which the eyes start to deviate inward when fixating on a near object. This test helps evaluate the accommodative component of esotropia.
• External Examination: Examine the external structures of the eyes and surrounding areas for any abnormalities, including eyelid position, symmetry, and signs of ptosis (drooping eyelid) or abnormal head posture.
• Refraction: Perform a cycloplegic refraction to determine the refractive error, particularly hyperopia (farsightedness), which is commonly associated with esotropia. Correcting refractive errors can sometimes improve or resolve the esotropia.
• Fundus Examination: Perform a fundus examination to evaluate the optic nerve, retina, and blood vessels for any abnormalities. This examination helps rule out any underlying ocular pathology or associated conditions.
• Additional Testing: Depending on the specific case and suspected etiology of esotropia, additional testing may be required. This can include neuroimaging (e.g., MRI) to assess for underlying neurological abnormalities, electroretinography (ERG) or visual evoked potentials (VEP) to evaluate visual function, or genetic testing if a genetic component is suspected.

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

Differential diagnosis

When evaluating a patient with esotropia, it is important to consider other possible conditions that can cause inward deviation of the eyes. The differential diagnosis of esotropia includes the following:

• Accommodative Esotropia: This is the most common type of esotropia in children and is associated with hyperopia (farsightedness). The inward eye turn occurs when the child tries to focus on near objects, leading to excessive convergence. It typically improves with corrective lenses.
• Convergence Insufficiency: In this condition, the eyes have difficulty converging properly, resulting in an outward deviation (exophoria) that can manifest as esotropia at near fixation. Symptoms may include eye strain, double vision, and difficulty with near tasks.
• Infantile Esotropia: Infantile esotropia refers to esotropia that presents during the first year of life. It is usually a constant inward deviation of the eyes and is not associated with refractive errors. It may be caused by abnormal development of the extraocular muscles or their neural control.
• Duane Syndrome: Duane syndrome is a congenital disorder that affects eye movement and is characterized by limited or absent abduction (outward eye movement). In some cases, it can lead to esotropia, especially when the affected eye attempts to fixate on objects in the direction of the limited movement.
• Acquired Esotropia: Esotropia can occur later in life due to various factors, including trauma, cataracts, neurologic disorders, or other ocular conditions. The underlying cause of acquired esotropia should be investigated and treated accordingly.
• Monocular Elevation Deficiency: Monocular elevation deficiency is a rare condition characterized by limited elevation of one eye, causing the eye to appear lower in the primary position. In some cases, esotropia may be present due to an abnormal head posture adopted to compensate for the limitation.
• Congenital Fibrosis of Extraocular Muscles: This is a rare genetic disorder that affects the development and functioning of the extraocular muscles. It can lead to various types of strabismus, including esotropia, due to restricted movement of the affected muscles.
• Neurologic Disorders: Certain neurologic conditions, such as brainstem lesions or cranial nerve palsies, can result in abnormal eye movements and esotropia. These conditions may have additional signs and symptoms beyond the eye misalignment.

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

The treatment of esotropia aims to correct the misalignment of the eyes, improve binocular vision, and address any underlying causes or associated conditions. The specific treatment approach depends on the type and severity of esotropia, the age of the patient, the presence of refractive errors or amblyopia, and other individual factors. Here are some common treatment options for esotropia:

• Glasses or Contact Lenses: If refractive errors, such as hyperopia, are present and contributing to the esotropia, prescription glasses or contact lenses may be prescribed. Correcting the refractive error can help improve the alignment of the eyes and reduce the need for excessive accommodation.
• Patching or Atropine: If amblyopia (lazy eye) is detected, treatment may involve patching or atropine drops. This involves covering the stronger eye to encourage the weaker eye to develop better vision. Patching therapy is typically combined with vision exercises and may be required for several hours a day.
• Vision Therapy: Vision therapy, also known as orthoptics or visual training, involves exercises and activities designed to improve eye coordination and strengthen the eye muscles. It is particularly beneficial for certain types of esotropia, such as convergence insufficiency. Vision therapy is typically conducted under the supervision of an optometrist or orthoptist.
• Prism Lenses: In some cases, prism lenses may be prescribed to help align the images seen by each eye, reducing the deviation. Prism lenses can be particularly useful for patients with small-angle or intermittent esotropia. However, they do not correct the underlying misalignment and are not a long-term solution.
• Botulinum Toxin Injection: Botulinum toxin (Botox) injections into the overactive extraocular muscles can be considered for specific cases of esotropia, such as infantile esotropia or sixth nerve palsy. This temporary treatment can weaken the muscles and allow for realignment of the eyes. Repeat injections may be needed over time.
• Surgery: Surgical intervention is often required for more persistent or severe cases of esotropia. The surgery aims to correct the alignment of the eyes by adjusting the tension or position of the extraocular muscles. The specific surgical approach depends on factors such as the magnitude and pattern of deviation, muscle imbalance, and associated conditions. Surgery is typically performed by an ophthalmologist specializing in strabismus surgery.

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References

https://www.ncbi.nlm.nih.gov/books/NBK578207/