Overview of Esotropia Types and Symptoms

Esotropia is a disorder in which the eyes aren't fully aligned and the affected eye(s) turn inward. It typically occurs in babies and children, but it can affect adults too. Esotropia is also associated with certain health conditions, including premature birth.

Esotropia in infants less than 20 weeks is common and usually resolves on its own. Treatment options for esotropia include the use of special glasses or eye patches. Eye muscle (strabismus) surgery may be considered when more conservative treatments fail to improve symptoms.

This article explains esotropia, its possible causes, and how it is diagnosed and treated. It also lists some of the health conditions that may increase the risk of esotropia in both children and adults.

Symptoms

The most common symptom of esotropia is crossed eyes, but it can also present with other symptoms, including:

• Eyes that look misaligned
• Eyes that turn inward
• Eyes that don't move together
• Squinting or turning your head to see better
• Eye strain
• Low vision
• Double vision (diplopia)
• Decreased depth perception

Types

There are several types of esotropia, and an eye care specialist will define the treatment based on certain characteristics:

• Age of onset: Esotropia can be congenital or acquired at any age.
• Frequency: Esotropia can be constant or intermittent. 
• Eye focusing: Esotropia can be caused by the eye straining to see clearly (accommodative vs. nonaccommodative).

Congenital Esotropia

Congenital esotropia, also known as infantile esotropia, develops within the first six months of life. Even though it is called congenital esotropia, this condition rarely presents at birth. The cause of congenital esotropia is unknown, but it is common and affects one in 50 newborns.

Transient misalignment of the eyes is common up to 3 months old, and should not be confused with infantile esotropia.

Acquired Esotropia

Acquired esotropia appears later in life, and can develop in children and adults as a result of injuries or diseases. A rare subtype of acquired esotropia called acute acquired comitant esotropia is characterized by sudden onset of a relatively large angle of esotropia, along with diplopia (double vision) and minimal refractive error, where the eye isn't bending light correctly, resulting in a blurred image.

Acquired esotropia is commonly treated with eyeglasses, but some cases may not improve with corrective lenses.

Constant Esotropia

Constant esotropia occurs when the eye is turned inward all the time. Most cases of esotropia are constant, but some cases of accommodative esotropia are intermittent.

Intermittent Esotropia 

The intermittency of accommodative esotropia is attributed to the fluctuating accommodative status of the patient as their eyes struggle to focus. Without treatment, intermittent esotropia is likely to turn into constant esotropia. The intermittent strabismus seen in infants is associated with normal development and typically goes away before 3 months of age.

Accommodative Esotropia

Accommodative esotropia, also known as refractive esotropia, refers to eye crossing that is caused by the focusing efforts of the eyes as they try to see clearly. The focusing effort is called accommodation. People with this type of esotropia usually have hyperopia (farsightedness), where a person can't see close objects clearly. It is common and comprises 50% of all childhood esotropia cases.

Accommodative esotropia can be classified into three types: refractive, non-refractive, and partially accommodative or decompensated. All three forms have an age of onset between 6 months and 7 years. It is frequently associated with amblyopia (lazy eye, or low vision due to abnormal visual development).

If the angle of the esotropia is fully corrected with glasses, the strabismus is said to be a fully accommodative esotropia. If the angle of the strabismus is not fully corrected with glasses, it is called a partially accommodative esotropia. Cases where there is no change in the angle of strabismus with glasses are nonaccommodative esotropia.

Nonaccommodative Esotropia

Acquired nonaccommodative comitant esotropia refers to a group of conditions not associated with accommodating effort. It is not connected to any refractive problems but can be associated with an intracranial tumor or other central nervous system (CNS) lesions.

Nonaccommodative esotropia can't be fixed with glasses. However, patients can often have this problem corrected with surgery.

Pseudoesotropia

With pseudoesotropia, the alignment of the eyes is actually straight but they appear to be crossed. Pseudoesotropia occurs in children with a broad, flat bridge of the nose and/or pronounced epicanthic folds (the upper eyelid skin that covers the eye's inner corner).

Pseudoesotropia is most common in infants with developing facial features and young children of Asian descent due to the anatomy of the Asian eye. Most children with pseudoesotropia outgrow this condition, and no treatment is needed.

Causes

Strabismus may run in the family. However, affected family members do not necessarily share the same type or severity of strabismus. A child with a family history of strabismus should be seen by a pediatric ophthalmologist. Other problems such as diabetes, hyperthyroidism, and neurologic problems can also cause esotropia.

In Children

Esotropia may be seen in children with very poor vision in one eye or in association with certain genetic disorders that affect the eyes. Children can also develop strabismus after congenital cataract surgery.

However, crossed eyes in childhood are usually caused either by idiopathic infantile esotropia, meaning the cause is unknown, with early onset within the first six to eight months of life, or accommodative esotropia, which is first noted between 1 and 4 years of age, in association with increased levels of farsightedness.

In Adults

Some conditions that can cause esotropia in adults include:

• Stroke: During a stroke, ocular motility abnormalities can occur, meaning abnormal eye alignment or difficulty in controlling eye movements, and result in strabismus. It is one of the most common features of stroke.
• Thyroid eye disease: Strabismus in thyroid eye disease is a result of inflammation and thickening of the extraocular muscles. This can restrict eye movement, causing misalignment and double vision.
• Neurodegenerative disorders: Maintaining proper eye alignment is necessary to generate a cohesive visual image. This involves the coordination of complex neural networks, which can become impaired by various neurodegenerative diseases. Therefore, different types of strabismus can be triggered by Huntington's or Parkinson's disease, for example.
• Sixth cranial nerve palsy:  Sixth cranial nerve palsy is a weakness of the nerve that innervates (supplies with nerves) the lateral rectus muscle, which controls the lateral movement of the eyeball. The lateral rectus muscle rotates the eye away from the nose. When the lateral rectus muscle is weak, the eye crosses inward toward the nose, resulting in esotropia.

Diagnosis

An eye care specialist diagnoses esotropia by taking a family history and performing a comprehensive eye exam. During the exam, they will pay close attention to how the eyes focus and move.

Tests and procedures used to diagnose strabismus include: 

• Corneal light reflex test: Also known as the Hirschberg test, this is a quick way to check ocular alignment, especially in young children. During the test, a person's attention is attracted to a target (a light or a brightly colored object), while light in front of them is directed at their eyes. This allows the specialist to check whether the eyes are symmetrical.
• Cycloplegic refraction: The eye care specialist will relax the focusing muscle of your eye using cycloplegic eye drops. This allows them to determine the complete refractive error. 
• Cover-uncover test: This test measures deviation and eye movement. Your eye care provider will ask you to fixate on a target. The specialist will cover one eye and observe how the uncovered eye responds. 
• Prism cover test: This test is used to measure the angle of deviation. Your eye care provider will use a prism bar to cover the misaligned eye, following the same direction as the deviation. 

Treatment

The main goals of treatment for esotropia include:

• Treating blurriness due to refractive errors
• Aligning the eyes
• Correcting amblyopia (lazy eye)
• Helping the eyes work together to focus

The choice of treatment depends on the severity of a person's symptoms and whether there are any specific treatment goals they wish to achieve.

Most babies outgrow intermittent strabismus by the age of 3 months, and there is no need for treatment. When the problem doesn't go away on its own, it can be treated with the following:

Glasses or Prism Lenses

Esotropia due to farsightedness is often resolved with glasses or contact lenses. In most people, corrective lenses will fix the over-focusing problem immediately. However, some people might still have esotropia while doing certain activities, such as reading, and an eye care specialist might prescribe bifocal lenses to treat it.

Certain types of esotropia, like partially accomodative esotropia, can be treated with prism lenses. Prism lenses have one side that is thicker than the other, and they change how the light enters the eye. It will reduce the effort the misaligned eye exerts when trying to focus on an object and improve the problem. 

Vision Therapy

Vision therapy for esotropia aims to correct misalignment, encourage the eyes to work together, and improve control of their movements. Training sessions often include exercises aimed at improving:

• Sensory fusion: The brain's ability to process what each eye sees as one united image
• Motor fusion: The control of eye muscles to adjust eye position
• Proprioceptive awareness: The unconscious awareness of the body's position in relation to its surroundings, for which vision plays an important role in gathering information

An optometric vision therapy program consists of supervised in-office and at-home reinforcement exercises performed over weeks to months. It is used in conjunction with other treatments, such as eye patches and glasses.

Botox Injections

The injection of botulinum toxin (botox) is considered a safe and effective alternative to surgery for correcting esotropia in adults and young children.

The treatment works by injecting botox into the medial rectus muscle, an eye muscle that, along with the lateral rectus, allows the eyes to move from side to side. Botox temporarily paralyzes the muscle, re-training the brain to focus both eyes together.

A research review on the effectiveness of botox for correcting congenital esotropia in infants found that the treatment significantly improves eye alignment in 76% of cases.

Surgery

Strabismus surgery involves making an incision in the conjunctiva to reach the eye muscles, isolating the problematic muscle, then loosening the muscle to relieve tension and re-set its resting position. No skin incisions are made during the procedure, which means the child will not have a visible scar.

Strabismus muscle surgery is typically done as an outpatient procedure, so the child can return home on the same day. After surgery, the white part of the child's eye may be red, and the eyes may feel scratchy or sore with movement. The soreness should improve within a few days, although the redness can take weeks to months to disappear.

Complications

Some conditions are complications of esotropia and their symptoms may overlap:

• Amblyopia is a condition that occurs when one or both eyes never see a clear image. If the image is never seen clearly for a long enough period of time, permanent vision loss may develop. After age 14, the brain and nervous system become hard-wired and it is difficult to improve vision back to normal. Therefore, early treatment is critical.
• Lack of true depth perception relies on distance between the eyes. When one eye is turned in or being suppressed, the person with esotropia only sees with one eye. People with esotropia have a difficult time with three-dimensional viewing, which may affect sports or job opportunities. 

Prognosis

Infantile esotropia can be easily treated with glasses or surgery, and children with this condition often grow up without vision problems.

When esotropia appears later in life, it can also be easily treated. However, it is essential to check if there are other underlying conditions that may be causing the misalignment. 

Summary

Esotropia is common in infants less than four months of age, for whom it usually goes away on its own. Symptoms of esotropia may include eyes that look misaligned or that don't move together, squinting or turning the head to see better, problems with depth perception, and double vision. Corrective glasses and eye patches are often effective for treating mild esotropia, whereas more severe esotropia may be treated with strabismus surgery, an outpatient procedure that does not leave a scar.