Strabismus: Symptoms, Types, Causes and Treatment

Strabismus, often referred to as "crossed eyes" or "wall-eyed," is a complex eye condition characterized by the misalignment of the eyes. This can affect a person’s vision, depth perception, and even their social or psychological well-being. Understanding strabismus is crucial not only for individuals and families affected by it but also for healthcare providers and educators aiming to support these individuals. This article provides a comprehensive exploration of strabismus, delving into its symptoms, types, causes, and available treatments, all underpinned by current scientific research.

Symptoms of Strabismus

Strabismus doesn't only affect how the eyes look; it can also have major impacts on vision and quality of life. Recognizing the symptoms early is vital for timely intervention, especially in children, to prevent long-term visual impairment and psychosocial effects.

Symptom	Description	Impact	Source(s)
Eye misalignment	One or both eyes turn in/out/up/down	Visible deviation, may be constant/intermittent	1, 3, 10
Double vision	Seeing two images of the same object (diplopia)	Disrupts daily activities, can cause confusion	3, 4, 5
Blurred vision	Lack of clarity in vision	Reduces reading ability, overall vision	2, 3
Eye fatigue	Tiredness or discomfort in the eyes	Difficulty with prolonged visual tasks	2, 3, 5
Headaches	Pain around eyes/forehead	May result from eye strain	3, 4
Difficulty estimating depth	Problems with 3D perception	Affects activities like driving or sports	2, 5
Low self-confidence	Psychosocial impact due to appearance	Social withdrawal, emotional distress	2, 3, 19

Table 1: Key Symptoms

Eye Misalignment: The Defining Feature

The most obvious sign of strabismus is when one or both eyes do not look in the same direction. This misalignment can be constant or only occur intermittently. The eyes may turn inward (esotropia), outward (exotropia), upward (hypertropia), or downward (hypotropia) 1, 10. Sometimes, the misalignment is subtle and only noticed during times of fatigue or when focusing on distant objects.

Visual Disturbances

Many people with strabismus experience visual symptoms such as:

• Double vision (diplopia): Common in acute or adult-onset strabismus, where the brain receives conflicting images from each eye. This is particularly disruptive and often prompts adults to seek care 3, 4.
• Blurred vision: The brain may suppress the image from the misaligned eye to avoid double vision, leading to blurry vision or even amblyopia ("lazy eye") if not treated, particularly in children 2, 3.
• Eye fatigue and headaches: Misaligned eyes require extra effort to maintain focus, leading to discomfort, headaches, and rapid visual fatigue, especially during tasks like reading or using screens 2, 3, 5.

Depth Perception and Daily Function

Strabismus can severely impact depth perception (stereopsis), making it difficult to judge distances. This can hinder activities such as driving, playing sports, or even simple tasks like pouring liquids 2, 5. In children, these challenges can affect learning and play.

Psychosocial and Emotional Impact

Beyond vision, the visible misalignment can lead to low self-confidence, poor self-image, social isolation, and even symptoms of depression and anxiety, especially in children and adults whose appearance is affected 2, 3, 19. Studies show that children with strabismus have higher levels of depression and anxiety, which can be improved after corrective treatment 19.

Types of Strabismus

Strabismus is not a single, uniform condition. It encompasses several subtypes, each with its own patterns, clinical presentations, and implications for treatment. Knowing the types aids in targeted management.

Type	Eye Movement Pattern	Common Age/Group	Source(s)
Esotropia	Eye(s) turn inward	Children > Adults	6, 10, 9
Exotropia	Eye(s) turn outward	Children, Asians/Africans	5, 6, 7, 10
Hypertropia	Eye(s) turn upward	Various ages	10, 13
Hypotropia	Eye(s) turn downward	Various ages	10, 13
Intermittent	Misalignment not constant	Often in exotropia	5, 10
Constant	Misalignment is always present	Severe cases	1, 10
Paralytic	Due to nerve/muscle impairment	Any age, often adults	13, 8, 12
Comitant	Deviation same in all gaze directions	Most childhood types	10, 8
Incomitant	Deviation varies with gaze	Neurological or restrictive	10, 13, 8

Table 2: Types of Strabismus

Horizontal Strabismus: Esotropia and Exotropia

• Esotropia: The most common type in children, where one or both eyes turn inward. Subtypes include accommodative (related to focusing efforts), partially accommodative, and non-accommodative esotropia 6, 10.
• Exotropia: Outward turning of the eye(s), which may be intermittent (especially in children and Asian or African populations) or constant. Intermittent exotropia is notable for sometimes being more prevalent in certain populations and often appears when looking at distant objects 5, 6, 7, 10.

Vertical Strabismus: Hypertropia and Hypotropia

Less common than horizontal types, vertical strabismus involves one eye being higher (hypertropia) or lower (hypotropia) than the other. These can result from trauma, nerve palsies, surgery, or restrictive conditions 10, 13.

Other Classifications

• Intermittent vs. Constant: Intermittent strabismus is not present all the time and can be more challenging to detect, whereas constant strabismus is always visible 1, 5, 10.
• Paralytic (Incomitant) vs. Non-paralytic (Comitant): Paralytic or restrictive strabismus occurs when an eye muscle or its nerve is damaged, leading to gaze-dependent misalignment. Comitant strabismus, where the degree of misalignment is consistent in all directions, is more commonly seen in children 10, 8, 13, 12.
• Syndromic and Age-related Types: Special forms include congenital cranial dysinnervation disorders (CCDD), often genetic, and “sagging eye syndrome” in older adults due to connective tissue changes 11, 12.

Causes of Strabismus

Strabismus can result from a wide range of anatomical, genetic, neurological, and environmental factors. Understanding these causes is key to effective prevention and management.

Factor	Mechanism/Description	Typical Presentation	Source(s)
Genetic	Inherited gene variants	Family history, early onset	12, 14, 15
Neurological	Impaired brain/nerve control	Paralytic/incomitant cases	4, 8, 15
Muscle/Anatomic	Extraocular muscle or pulley issues	Restrictive or age-related strabismus	11, 13
Refractive Error	Uncorrected vision problems	Accommodative esotropia	10, 6
Prematurity/Perinatal factors	Birth complications, hypoxia	Early childhood cases	5, 10
Systemic Disease	Conditions like cerebral palsy	Higher prevalence, complex types	9, 15
Trauma/Surgery	Injury or post-surgical effect	Acquired, sometimes transient	13, 11
Environmental	Screen time, visual stress	May contribute to onset	3, 10

Table 3: Causes of Strabismus

Genetic and Developmental Origins

Many cases, particularly those with onset in early childhood, have a genetic basis. Recent studies have identified specific genetic loci, such as variants in the NPLOC4–TSPAN10–PDE6G gene cluster, associated with increased risk 14. More complex congenital forms are linked to mutations affecting brainstem motoneuron development 12. Family history is a significant risk factor 3, 15.

Neurological and Central Mechanisms

Strabismus can arise from anomalies in the central neural pathways responsible for binocular vision and eye movement coordination. This is especially relevant for comitant strabismus, where the extraocular muscles themselves are structurally normal but their neural control is disrupted 8, 15. Acute strabismus in children may signal underlying neurological emergencies, such as brain tumors, particularly when accompanied by other neurological symptoms 4.

Ocular and Anatomical Factors

Abnormalities in the extraocular muscles or their connective tissue supports (such as in sagging eye syndrome) can cause strabismus, especially in older adults 11. Surgical interventions, such as cataract surgery, can also lead to strabismus if eye muscles are inadvertently affected 13.

Refractive and Visual Factors

Uncorrected refractive errors, especially farsightedness (hyperopia), can lead to accommodative esotropia, where the eyes cross to compensate for blurred vision 6, 10. Early correction of refractive errors can prevent or reduce the risk of developing certain types of strabismus.

Systemic and Environmental Contributors

Certain systemic diseases, particularly cerebral palsy, have a much higher prevalence of strabismus, often with more severe or complex forms 9. Prematurity and perinatal complications, including hypoxia during birth, are also recognized risk factors 5, 10. Environmental factors, such as excessive screen time, may be associated with increased risk, though evidence is still emerging 3, 10.

Treatment of Strabismus

The good news is that strabismus is treatable at any age. Early intervention is critical for children to prevent lasting vision problems, but adults can also benefit significantly, both functionally and cosmetically.

Treatment	Description	Typical Use/Population	Source(s)
Glasses	Correct refractive errors	Accommodative esotropia, children	1, 6, 10
Vision Therapy	Exercises to improve coordination	Mild/intermittent cases	1, 3
Surgery	Adjusts eye muscles/alignment	Most types, children/adults	1, 16, 19
Botulinum Toxin	Temporarily weakens muscles	Select cases, adults/children	16, 17, 18, 20
Prisms/patches	Manage double vision, amblyopia	Selected cases, children	1, 3
Treat underlying cause	Neurological, systemic, trauma	As needed	4, 8, 13

Table 4: Main Treatment Options

Nonsurgical Interventions

• Glasses: For children with accommodative esotropia, prescription lenses are often the first step. Correcting underlying refractive errors can, in some cases, resolve the misalignment without further intervention 1, 6, 10.
• Vision therapy: Eye exercises and visual training may help improve eye coordination, particularly in cases of intermittent strabismus 1, 3.
• Prisms and patches: Prisms can be used in glasses to alleviate double vision, while eye patching is often used in children to treat amblyopia by forcing use of the weaker eye 1, 3.

Surgical Treatment

Eye muscle surgery remains the mainstay for cases not fully correctable with nonsurgical methods. This can involve tightening or loosening specific eye muscles to achieve proper alignment. Surgery is effective in both children and adults, with reported realignment success rates of 68% to 85% 16. In addition to cosmetic improvement, surgery can restore binocular vision, reduce double vision, and improve quality of life 16, 19.

• Psychological benefits: Especially for children, surgical correction has been shown to significantly reduce symptoms of depression and anxiety, improving social confidence and emotional well-being 19.

Botulinum Toxin (Botox) Injections

For selected cases, particularly small-angle or certain paralytic types, botulinum toxin injections can temporarily weaken overactive eye muscles. While less effective than surgery for most comitant types, it can be useful in specific circumstances (e.g., recent surgical overcorrection, some nerve palsies) 16, 17, 18, 20. Complications may include temporary ptosis or vertical deviation 18, 20.

Treating Underlying or Associated Conditions

When strabismus is due to a neurological, systemic, or traumatic cause, addressing the underlying disease is crucial. For example, prompt treatment of brain tumors or avoidance of muscle injury during eye surgery can prevent or resolve secondary strabismus 4, 8, 13.

Conclusion

Strabismus is a multifaceted condition with significant visual, functional, and psychosocial implications. Early recognition and intervention are crucial, especially in children, to preserve vision and quality of life. Advances in genetics, neurobiology, and surgical techniques continue to improve outcomes for people with strabismus worldwide.

Key Points Summarized:

• Strabismus is defined by misalignment of the eyes and can cause double vision, blurred vision, eye fatigue, and major psychosocial effects 1, 2, 3.
• Types include esotropia, exotropia, vertical deviations, intermittent/constant, comitant/incomitant, and more, each with specific clinical features 5, 6, 10, 11.
• Causes are varied: genetic, neurological, muscular, refractive, environmental, or systemic disease-related 8, 12, 14, 15.
• Treatment options range from glasses and vision therapy to surgery and botulinum toxin injections, tailored to the type and cause. Early intervention, especially in children, is critical for optimal outcomes 1, 6, 16, 18.
• Strabismus affects quality of life, but effective management can restore vision, confidence, and emotional well-being 2, 19.

By increasing awareness and understanding, we can ensure that those with strabismus receive the care and support they need to thrive.