Overview
Definition:
Strabismus is a misalignment of the eyes where they do not point in the same direction
Amblyopia, or "lazy eye," is reduced vision in one eye that does not develop properly during early childhood, often associated with uncorrected strabismus, refractive errors, or deprivation
Optimal timing of strabismus surgery and concurrent amblyopia therapy is critical for achieving binocularity and preventing long-term visual impairment.
Epidemiology:
Strabismus affects approximately 2-5% of children
Esotropia (inward turning) is the most common type, followed by exotropia (outward turning)
Amblyopia occurs in 2-5% of the pediatric population, with strabismic amblyopia being a significant contributor.
Clinical Significance:
Untreated strabismus can lead to amblyopia, loss of binocular vision (stereopsis), and cosmetic concerns, impacting a child's self-esteem and social interactions
Early intervention significantly improves visual outcomes and the potential for developing functional binocular vision.
Clinical Presentation
Symptoms:
Intermittent or constant eye turning
Head tilting or abnormal head posture
Drooping eyelid (ptosis) that may cause the child to close one eye
Poor depth perception
Double vision (diplopia), though often suppressed in children
Children may not complain of visual symptoms due to suppression.
Signs:
Visible misalignment of the eyes (tropia) or a tendency for misalignment when binocular fusion is broken (phoria)
Unequal corneal light reflexes (Krimsky test)
Poor fixation in one eye on cover testing
Reduced visual acuity in one eye on Snellen charts or other age-appropriate tests
Fundus examination may reveal optic nerve pallor in severe amblyopia
Fundus examination may reveal optic nerve pallor in severe amblyopia.
Diagnostic Criteria:
Diagnosis is based on clinical examination, including cover tests (unilateral and alternating), assessment of visual acuity (e.g., Lea Symbols, HOTV, Teller Acuity Cards), refractive error assessment (cycloplegic refraction is crucial), and assessment of ocular alignment
Criteria for strabismus include a manifest deviation detected by cover testing
Amblyopia is diagnosed by reduced visual acuity not correctable by refractive error alone and not attributable to other ocular pathology.
Diagnostic Approach
History Taking:
Age of onset of eye deviation
Family history of strabismus, amblyopia, or significant refractive errors
Any history of prematurity, birth trauma, or perinatal complications
History of visual symptoms like eye rubbing, head tilting, or closing one eye
Prior interventions or diagnoses
History of neurological conditions.
Physical Examination:
Visual acuity assessment (using age-appropriate charts and methods)
Cycloplegic refraction (essential to detect significant hyperopia, myopia, or astigmatism)
Cover testing (unilateral, alternating, and prolonged cover tests) to assess for tropias and phorias and their magnitude
Ocular motility assessment to detect restrictions or limitations
Examination of pupils for afferent pupillary defect (APD)
Red reflex and fundus examination to rule out other ocular pathologies like cataracts or retinoblastoma.
Investigations:
Cycloplegic refraction with a cycloplegic agent like cyclopentolate or tropicamide is paramount
Visual acuity testing with age-appropriate charts
Cover tests (unilateral, alternating, prolonged) are the cornerstone
Prism cover tests to quantify phorias
Fundus examination (dilated) to rule out other causes of reduced vision
Optical coherence tomography (OCT) or MRI may be considered if neurological causes are suspected.
Differential Diagnosis:
Pseudostrabismus (e.g., epicanthal folds, prominent interpupillary distance)
Cranial nerve palsies (e.g., III, IV, VI nerve palsies)
Congenital cataracts or other media opacities causing deprivation amblyopia
Refractive amblyopia (anisometropia, bilateral high refractive error)
Neurological conditions affecting eye movements (e.g., Duane syndrome, congenital nystagmus)
Optic nerve hypoplasia.
Management
Initial Management:
The primary goals are to restore normal visual acuity in the amblyopic eye and achieve ocular alignment to restore binocular vision
This involves addressing refractive errors and treating amblyopia before or concurrently with strabismus surgery.
Amblyopia Therapy:
Correction of refractive error (glasses or contact lenses) is the first step
Patching therapy (full-time patching of the better-seeing eye) or atropine penalization (using atropine drops in the better-seeing eye to blur vision) is used to force the use of the amblyopic eye
Duration and intensity depend on age and severity
typically continued until visual acuity is equal or near-equal, and then gradually reduced
Intervention is most effective before age 7-8, but can be beneficial in older children.
Surgical Management:
Indications for surgery include significant and persistent strabismus that is not responsive to other treatments, or when alignment significantly impacts binocular function and stereopsis
Timing is crucial: aiming for surgery when amblyopia is well-controlled and the child is neurologically stable
For constant, significant deviations, surgery may be considered earlier, especially if it interferes with normal visual development or causes persistent diplopia
For intermittent exotropia, surgery may be delayed to assess for progression and potential for non-surgical management.
Postoperative Care:
Postoperative management includes antibiotic eye drops and steroid eye drops for a specified period
Pain management is usually minimal
Close follow-up is essential to monitor for healing, recurrence of strabismus, and any residual amblyopia
Continued patching may be necessary if amblyopia recurs
Vision therapy may be employed to optimize binocular function post-surgery.
Timing Considerations
Age And Visual Development:
The critical period for binocular vision development is generally considered to be up to age 7-8
Early intervention for amblyopia and strabismus is paramount to maximize the chances of achieving good visual acuity and stereopsis
Surgery is often postponed in infants and very young children with strabismus if there is a good prognosis for developing fusion with amblyopia treatment alone, but performed when deviation is constant, large, or leads to suppression.
Amblyopia Status:
Amblyopia should ideally be treated and its visual acuity improved significantly (ideally to within 1-2 lines of the fellow eye) before elective strabismus surgery, especially for larger deviations
However, in some cases of constant strabismus with significant impact on binocularity or social appearance, surgery may precede full amblyopia recovery
Severe amblyopia may be a relative contraindication for immediate surgery if its impact on visual outcome is minimal compared to the surgical risks.
Type And Magnitude Of Strabismus:
Large angle constant strabismus, especially esotropia in infants, may warrant earlier surgical intervention to facilitate binocular vision development
Intermittent exotropia may be monitored longer, with surgery considered if it becomes constant or causes significant symptoms
Vertical strabismus often requires prompt assessment and management due to its impact on head posture.
Patient And Family Factors:
The child's overall health, cooperation with treatment (e.g., patching), and the family's ability to follow up and manage post-operative care are crucial considerations
Parental understanding and adherence to the treatment plan are vital for success.
Complications
Early Complications:
Infection (endophthalmitis - rare)
Corneal abrasion or ulceration
Significant chemosis or edema
Persistent diplopia
Wound dehiscence.
Late Complications:
Recurrence of strabismus
Under- or over-correction
Adhesions and scarring
Ptosis or lid retraction
Development or worsening of amblyopia
Loss of vision (extremely rare)
Diplopia in primary or reading positions
Fibrosis of muscles.
Prevention Strategies:
Strict sterile surgical technique
Appropriate use of perioperative antibiotics and steroids
Accurate preoperative assessment and surgical planning
Careful wound closure
Close postoperative monitoring
Prompt management of any complications
Continued amblyopia therapy as needed.
Prognosis
Factors Affecting Prognosis:
Age at onset of strabismus and amblyopia
Severity of amblyopia
Type and magnitude of strabismus
Presence and degree of binocular function prior to intervention
Consistency of amblyopia treatment adherence
Quality of surgical correction
Presence of associated ocular or neurological conditions.
Outcomes:
With timely and appropriate intervention, the prognosis for restoring good visual acuity and achieving functional binocular vision is generally favorable, especially in younger children
Successful surgery can significantly improve ocular alignment, reduce or eliminate diplopia, and enhance cosmetic appearance
Stereopsis may be regained in some cases, particularly with early and effective treatment.
Follow Up:
Long-term follow-up is essential, often extending into adolescence
This includes regular assessment of visual acuity, refractive status, ocular alignment, and binocular function
Early detection of recurrence or regression of amblyopia allows for prompt re-intervention
Annual or bi-annual checks are typical for children treated for strabismus and amblyopia.
Key Points
Exam Focus:
Prioritize the definition and impact of strabismus and amblyopia
Understand the goals of treatment: visual acuity restoration and binocular alignment
Recognize the critical role of cycloplegic refraction
Differentiate types of amblyopia (strabismic, refractive, deprivation)
Master the principles of patching and penalization therapy.
Clinical Pearls:
Always perform a cycloplegic refraction in children with suspected strabismus or significant refractive errors
Do not underestimate the impact of even small refractive errors on visual development
For intermittent exotropia, observe for progression and consider the impact of fatigue and illness on deviation
Reassure parents that amblyopia therapy can be challenging but is crucial for long-term vision
Consider surgery after amblyopia has been adequately treated unless the strabismus itself severely compromises visual development.
Common Mistakes:
Failing to perform cycloplegic refraction
Delaying amblyopia treatment
Performing strabismus surgery before adequate amblyopia treatment
Underestimating the importance of binocular vision and stereopsis
Inadequate postoperative follow-up leading to recurrence or undertreatment of amblyopia
Assuming amblyopia is irreversible after a certain age without trying therapy.