What is Strabismus?
Strabismus is misalignment of the eyes where one eye deviates while the other fixates on an object, resulting in failure of both eyes to simultaneously focus on the same image and loss of binocular vision. 1
Definition and Prevalence
Strabismus can be:
- Congenital (present at birth) or acquired later in life
- Although commonly associated with children, it affects approximately 4% of adults 1
- Annual incidence of new-onset adult strabismus is estimated at 4% of the adult population 1
Types of Strabismus
Strabismus can be classified based on the direction of eye deviation:
- Esotropia: Inward turning of the eye (convergent)
- Exotropia: Outward turning of the eye (divergent)
- Hypertropia/Hypotropia: Vertical misalignment (upward/downward deviation)
- Cyclotropia: Rotational misalignment
Additionally, strabismus can be:
- Comitant: The angle of deviation remains the same in all directions of gaze
- Incomitant: The angle varies depending on the direction of gaze
Common Causes of Strabismus
In Adults
- Recurrent or unresolved childhood strabismus
- Sensory strabismus (from vision loss in one eye)
- Convergence insufficiency
- Divergence insufficiency
- Sagging eye syndrome (common in older adults)
- High axial myopia
- Graves' disease
- Orbital trauma
- Post-surgical complications
- Cranial nerve palsies (3rd, 4th, 6th)
- Myasthenia gravis
- Fixation switch diplopia 1
Underlying Mechanisms
- Abnormalities in extraocular muscles
- Neurological disorders affecting oculomotor control
- Central nervous system involvement in visual processing
- Genetic factors 2, 3, 4, 5
Clinical Manifestations
The most common symptoms and signs include:
- Misalignment of the eyes
- Double vision (diplopia), especially in adult-onset cases
- Reduced depth perception
- Abnormal head posture (to compensate for misalignment)
- Eye strain and headaches
- Difficulty with reading or near work
- Psychosocial impacts (self-esteem, social interactions) 1
Diagnosis
Diagnosis requires a comprehensive ophthalmologic examination including:
- Visual acuity testing
- Ocular alignment assessment (cover test)
- Ocular motility evaluation
- Cycloplegic refraction
- Assessment of binocular function
- Neurological evaluation when indicated 1
Treatment Options
Treatment aims to:
- Restore binocular vision when possible
- Eliminate diplopia
- Improve ocular alignment for functional and cosmetic purposes
- Enhance quality of life and psychosocial functioning 1
Non-surgical Options
- Optical correction (glasses, prisms)
- Orthoptic exercises (for certain types like convergence insufficiency)
- Botulinum toxin injections (temporary weakening of extraocular muscles) 1, 6
Surgical Options
- Strabismus surgery (recession, resection, or transposition of extraocular muscles)
- Success rates are approximately 80% after one procedure and may exceed 95% with a second procedure 1
- Risk of intractable postoperative diplopia is less than 1% 1
Complications and Prognosis
- Untreated strabismus can lead to amblyopia (lazy eye) in children
- Persistent diplopia can significantly impact quality of life
- Psychosocial impacts include reduced self-esteem and social difficulties
- With appropriate treatment, many patients experience significant improvement in both functional vision and quality of life 1
Important Considerations
- Early detection is crucial, especially in children, to prevent amblyopia
- Adult strabismus is not merely cosmetic and warrants treatment
- Treatment of strabismus in adults can significantly improve quality of life
- Botulinum toxin injections require caution due to potential side effects including spatial disorientation and double vision 6