OVERVIEW

What is strabismus?

Strabismus refers to the condition where both eyes cannot simultaneously focus on a single target, with one eye fixating while the other deviates to the opposite side of the target.

The human brain integrates the images seen by both eyes into a single image, with the highest-level function being stereopsis. Stereopsis is crucial for professions requiring precise eye coordination, such as scientists using microscopes, surgeons performing operations, or soldiers engaged in shooting.

Binocular vision typically fully develops by the age of 12. If strabismus is not corrected before this age, it may prevent the establishment of binocular vision, thereby affecting an individual's future development.

SYMPTOMS

What are the hazards of strabismus?

• Strabismus patients may look different from others in appearance, often leading to nicknames, which can cast a psychological shadow on the patient, potentially resulting in introversion, low self-esteem, and other abnormal psychological states.

• Strabismus can cause "strabismic amblyopia," leading to reduced vision. Even if the patient is fortunate enough not to develop amblyopia, they typically use only one eye to see, resulting in a much narrower field of vision compared to normal individuals. Additionally, strabismus patients generally lack binocular fusion and stereoscopic vision, limiting their ability to work in many professional fields, such as driving, drafting, and other jobs that require high visual demands.

• Strabismus patients may experience discomfort when looking at objects, often adopting compensatory head positions like tilting their head or turning their face to alleviate the discomfort. If not treated promptly, this can lead to skeletal issues such as scoliosis. If children and adolescents do not seek timely medical treatment, it may also cause facial skeletal deformities.

What are the types of strabismus?

Strabismus is usually classified by the direction of deviation into horizontal strabismus and vertical strabismus:

• Horizontal strabismus includes esotropia (commonly known as "crossed eyes") and exotropia (outward deviation). Generally, esotropia can be congenital or acquired. Exotropia can be intermittent (sometimes deviated, sometimes not) or constant (permanent deviation).

• Vertical strabismus includes hypertropia (upward deviation) and hypotropia (downward deviation). Vertical strabismus is often accompanied by head tilting.

Based on changes in eye position deviation in different gaze directions, strabismus can be classified into comitant strabismus and incomitant strabismus:

• Comitant strabismus: The degree of eye deviation does not change with the direction of gaze or with which eye is used for fixation.

• Incomitant strabismus: The degree of eye deviation changes with the direction of gaze and with which eye is used for fixation. Most incomitant strabismus is paralytic or restrictive. If it is acquired incomitant strabismus, it may indicate neurological or orbital diseases.

What are the manifestations of paralytic strabismus?

• Deviation of the eye in one or multiple gaze directions.

• Limited eye movement function, with reduced ability of one or both eyes to turn in certain directions, or even complete inability to move the eye.

• Head tilting or turning (compensatory head posture): To avoid double vision, patients often tilt their head or adjust their head position upward or downward.

• Double vision or fatigue: Acquired paralytic strabismus may cause blurred vision or eye fatigue in mild cases, and dizziness, nausea, or vomiting in severe cases. Patients often tilt their head to reduce or eliminate double vision.

CAUSES

Can hyperopia cause strabismus?

People with hyperopia can also develop strabismus. This type of strabismus is generally referred to as accommodative esotropia. Depending on its severity, it can be classified into fully accommodative esotropia and partially accommodative esotropia:

• Fully accommodative esotropia: This type of strabismus is common in children and usually disappears after proper optometry and wearing corrective glasses.

• Partially accommodative esotropia: This refers to cases where, even after full correction of hyperopia, esotropia persists while wearing glasses. Generally, such strabismus requires surgical treatment followed by glasses to restore basic functionality.

What are the common causes of incomitant strabismus?

Incomitant strabismus usually has identifiable causes, such as trauma or systemic diseases affecting the eyes.

What are the common causes of comitant strabismus?

The exact causes of comitant strabismus remain unclear and may involve multiple factors or a combination of influences. Common causes include:

• Refractive errors: Hyperopic patients may develop accommodative esotropia due to excessive convergence, while myopic patients, who use less accommodation, may develop exotropia.

• Sensory deprivation: Conditions like corneal opacity, congenital cataracts, or vitreous opacity can impair vision, preventing binocular fusion in the brain and leading to strabismus.

• Genetic factors: Children of parents with strabismus have a slightly higher likelihood of developing it, though it is not guaranteed.

Can both adults and children develop strabismus?

• Adult strabismus mainly results from untreated childhood strabismus or later-life incidents such as trauma, tumors, or weakening of binocular fusion. Since adults have fully developed visual functions, strabismus surgery primarily aims to improve appearance. For adults with diplopia, certain surgeries may eliminate double vision and enhance quality of life.

• Childhood strabismus is categorized as congenital or acquired. Strabismus occurring before six months is often congenital esotropia, while acquired strabismus develops later, possibly due to trauma, tumors, or other causes. Treatment in children focuses not only on appearance but also on functional development, particularly preserving stereopsis.

What are the common causes of paralytic strabismus?

• Trauma;
• Inflammation: e.g., meningitis, sinusitis, orbital cellulitis;
• Cerebrovascular diseases; orbital, optic nerve, or intracranial tumors;
• Other systemic diseases.

What is the relationship between strabismus and diplopia?

Generally, binocular diplopia indicates the presence of strabismus. Some patients with diplopia may not show obvious strabismus externally, but examination will reveal it.

However, strabismus does not always cause diplopia. For example, congenital strabismus typically does not result in diplopia.

DIAGNOSIS

How is strabismus diagnosed?

Generally, larger degrees of strabismus are easier to detect.

If the degree of strabismus is small, it requires professional examination to be identified. Carefully observe the "subject." If there are signs such as tilting the head, turning the face sideways, spinal curvature, or noticeably narrow vision while looking at objects, strabismus may be suspected.

Is it strabismus if the black part of the eye is not centered in the white part?

Normally, both eyes should gaze straight ahead at a target. If the black part of one eye is centered in the white part while the other is not, with a significant deviation from the center, strabismus is likely.

However, some children may have underdeveloped nasal bridges, making the white part near the nose appear smaller, resembling crossed eyes. This is a "pseudo" esotropia and requires professional medical evaluation.

In rare cases, a patient's eye position may appear normal when looking straight ahead. Additional tests, such as looking to the upper left or right, may be needed to detect conditions like congenital superior oblique muscle palsy.

What is intermittent exotropia?

Some people may appear normal at times but occasionally exhibit outward eye deviation, known as intermittent exotropia.

These individuals usually have good binocular fusion ability and can maintain normal eye alignment most of the time. However, it may occur in sunlight, during eye fatigue, or when attention is unfocused—for example, a child squinting one eye in sunlight.

Initially, this type of strabismus occurs infrequently with small angles, making it hard to notice. Over time, the frequency increases, and the angle gradually widens, eventually progressing to constant exotropia.

Is it strabismus if a child often tilts their head while looking at things?

If a child consistently tilts their head to one side, parents should take it seriously. It may indicate strabismus.

However, it's important to distinguish whether the head tilt is due to strabismus or muscular/cervical issues (torticollis). If uncertain, consult a professional medical examination.

How can parents check if their child has strabismus?

Shine a flashlight on the bridge of the child's nose. Two reflection points will appear in the eyes. If these points are not centered in the black part of the eyes, strabismus may be present.

The best way to confirm is through a professional medical examination.

Why is there no strabismus detected despite severe crossed eyes?

Pseudoesotropia is a type of strabismus where the eyes appear crossed, but professional examination reveals no actual deviation.

This occurs because the child's facial development is incomplete, with a flat nasal bridge and epicanthal folds—a common eyelid shape in many East Asians—making the inner white part of the eyes less visible, creating the illusion of crossed eyes.

What is paralytic strabismus?

Paralytic strabismus is a type of non-comitant strabismus, including various congenital and acquired forms. If it occurs early in infancy, it often accompanies head tilting. Untreated, it can affect appearance, facial development, and even lead to amblyopia or binocular vision dysfunction.

It may impact future schooling and employment, so early detection and treatment are crucial.

What is sensory exotropia?

Sensory exotropia occurs when one eye has very poor vision, weakening the ability to maintain alignment, causing the weaker eye to gradually deviate outward.

Strabismus surgery does not improve vision, so the risk of continued exotropia due to poor vision remains. The success rate of surgery is about 50%.

To prevent recurrence, doctors may slightly overcorrect the surgery, leaving the patient with a mild inward deviation post-operation.

TREATMENT

Does all strabismus require surgery?

It cannot be generalized. Small-angle strabismus can be treated with prism glasses. Accommodative esotropia only requires wearing hyperopic glasses. However, some types of strabismus, especially large-angle congenital esotropia and vertical strabismus, do require surgical treatment.

What is the best time for strabismus treatment?

• For children with concomitant esotropia, early treatment is recommended. If not treated in time, they may lose binocular vision after age 12. Even if surgery corrects the strabismus later, it will only serve a cosmetic purpose.

• For mild strabismus, the timing of surgery can be determined based on visual function.

• For non-concomitant strabismus, surgery is usually performed at least six months after onset, once the angle stabilizes.

What is the success rate of strabismus surgery?

The success rate depends on factors such as the child's age, degree of refractive error, type of strabismus, dominant eye, and presence of binocular vision.

For concomitant strabismus, the success rate of a single surgery can exceed 90%. Strabismus surgery does not affect vision or compromise the eye's integrity, with a relatively low infection risk and high safety.

Of course, the surgeon's skill also plays a crucial role. Early treatment at a reputable hospital is advised.

Is the treatment the same for concomitant and non-concomitant strabismus?

No, treatments differ.

Does intermittent exotropia require surgery?

Most cases of intermittent exotropia require surgery, but the optimal timing is not clearly defined. Since its impact on binocular vision is less severe than esotropia, surgery is not usually the first choice.

However, if the exotropia becomes more frequent, the angle increases significantly, affects appearance, or progresses to constant exotropia, surgery should be considered.

Is the recurrence rate high after intermittent exotropia surgery?

There is a recurrence probability of about 10%.

Recurrence is influenced by multiple factors, including whether the preoperative examination accurately identifies the maximum deviation angle for surgical planning.

Additionally, patient anxiety during surgery and the brain's ability to fuse images cannot be altered by surgery, which may also affect recurrence.

Why does the surgeon recommend operating on the right eye if my left eye has strabismus?

This often occurs in concomitant strabismus, where muscle imbalance between the eyes causes misalignment. Adjusting either eye can restore alignment.

Common reasons for operating on the right eye include:

• The left eye, despite strabismus, has better vision. Surgery on the weaker right eye reduces risk to the dominant eye.

• If the right eye is noticeably larger, muscle shortening during surgery can balance eye size for a more harmonious appearance.

Other factors, such as prior left-eye surgery limiting muscle adjustment, may also justify operating on the right eye.

How should anesthesia be chosen for a child undergoing strabismus surgery?

Options include general anesthesia (GA) and local anesthesia (LA).

• GA is used for children under 12 or those with low pain tolerance. Since eye position cannot be adjusted intraoperatively, preoperative measurements must be precise.

• LA allows intraoperative eye position observation. Most children over 12 tolerate LA well, and some younger children with high pain tolerance may also qualify.

Is adult strabismus correction only for cosmetic purposes?

No. Adult strabismus correction aims to:

• Alleviate double vision or visual fatigue, improving daily life.

• Enhance emotional well-being and social interactions by improving appearance.

Why is strabismus surgery sometimes performed in stages?

Large-angle strabismus or combined horizontal/vertical deviations may require multiple muscle surgeries. Operating on more than two rectus muscles in one eye risks anterior segment ischemia.

Thus, additional surgeries are scheduled 2–3 months later after blood supply recovery. Inaccurate preoperative measurements due to poor cooperation may also necessitate adjustments.

Does strabismus surgery require hospitalization?

Adult surgeries under LA are typically outpatient procedures. Complex cases (e.g., high myopia-induced esotropia or thyroid-related strabismus) may require GA and hospitalization.

Children under 12 usually need hospitalization: admission day for tests, surgery the next day, observation, and discharge on the third day.

Can strabismus and myopia surgeries be performed simultaneously?

No. Laser myopia surgery damages the cornea, and immediate strabismus surgery risks further injury. The sequence depends on individual cases.

Can both eyes be operated on simultaneously for strabismus?

• Large-angle concomitant strabismus may allow bilateral surgery.

• Non-concomitant cases vary. Complex cases (e.g., involving oblique muscles or prior surgeries) may require staged procedures due to unpredictable outcomes.

Is recurrence common after strabismus surgery?

Recurrence is rare, but notable exceptions include:

• Intermittent exotropia in children (~10% recurrence due to immature binocular vision and GA limitations).

• Dissociated exotropia (~50% recurrence due to absent binocular vision).

• Progressive strabismus (e.g., endocrine-related) may recur if the underlying condition relapses.

DIET & LIFESTYLE

Can I use a computer after strabismus surgery? Can I return to work normally?

Strabismus surgery does not alter vision, but redness and swelling may occur the next day, potentially affecting normal work. It is advisable to limit eye use appropriately in the early postoperative period.

Post-surgery, hormone and antibiotic eye drops should be used as prescribed to reduce inflammation and prevent infection.

The whites of the eyes may appear red due to surgical wounds, but this typically subsides within about a month and does not interfere with daily work or life.

PREVENTION

How to Prevent Strabismus?

For strabismus caused by trauma, timely and standardized treatment is required to minimize eye damage; for idiopathic comitant strabismus, there is currently no effective treatment.