Part III - Binocular Vision II | 6th Semester Bachelor of Optometry

Amblyopia and Its Management

Introduction:

Amblyopia, commonly known as "lazy eye," is a neurodevelopmental disorder of vision characterized by decreased visual acuity in one or both eyes that is not attributable to any structural abnormality. It arises due to abnormal visual experience during the critical period of visual development, typically before the age of 7 to 8 years. The prevalence of amblyopia is approximately 2–4% in children, making it one of the most common causes of preventable vision loss in childhood. If not managed early, amblyopia can lead to permanent visual impairment and reduced binocular vision throughout life.

Definition of Amblyopia

Amblyopia

Amblyopia is defined as a reduction in best-corrected visual acuity of one or both eyes caused by abnormal visual development, without any detectable organic pathology in the visual pathway or ocular structures. The vision loss is functional and is due to inadequate stimulation of the visual cortex from one eye during the sensitive period of visual development.

Causes and Types of Amblyopia

Amblyopia results from a disruption in normal visual input, and is classified into the following major types:

1. Strabismic Amblyopia

Occurs due to a constant squint (usually esotropia) where the brain suppresses the image from the deviated eye to avoid diplopia and confusion. Suppression over time leads to cortical underdevelopment of the deviated eye.

2. Anisometropic Amblyopia

Caused by a significant difference in refractive error between the two eyes, leading the brain to favor the clearer image from one eye while suppressing the blurred image from the other. It is often undiagnosed until school age and can occur without strabismus.

3. Deprivation Amblyopia

Results from physical obstruction of the visual axis (e.g., congenital cataract, ptosis, corneal opacity) in early infancy. It is the most severe form and requires urgent treatment to prevent irreversible visual loss.

4. Meridional Amblyopia

Occurs when uncorrected astigmatism blurs certain orientations of the visual field, leading to selective underdevelopment of the corresponding visual cortex areas.

5. Stimulus Deprivation Amblyopia

A broader category that includes any condition (e.g., prolonged patching, occlusion, or trauma) that limits form vision to one or both eyes during the critical developmental window.

Risk Factors

Constant unilateral strabismus
High or unequal refractive error
Family history of amblyopia or strabismus
Premature birth or low birth weight
Developmental delays or syndromes
Ocular pathologies (e.g., cataract, ptosis, corneal scar)

Clinical Features of Amblyopia

Reduced best-corrected visual acuity in one or both eyes
Normal ocular health upon examination
Poor stereopsis (loss of depth perception)
Suppression of the amblyopic eye under binocular conditions
May present with or without noticeable strabismus
Possible fixation instability or eccentric fixation

Diagnosis of Amblyopia

Diagnosis involves a comprehensive optometric examination, including:

Visual acuity testing: Age-appropriate charts (Lea symbols, HOTV, Snellen)
Refraction: Cycloplegic refraction is critical to detect latent hyperopia or anisometropia
Ocular health assessment: Rule out organic causes
Binocular vision testing: Stereopsis tests (Titmus fly, Randot), Worth four-dot, Bagolini lenses
Cover test: To check for strabismus or latent deviations

Management of Amblyopia

Management strategies are aimed at encouraging the use of the amblyopic eye and promoting visual development. Treatment is most effective when initiated before age 7, although older children and even adults may show improvement with structured therapy.

1. Optical Correction

All amblyopic patients should be prescribed full refractive correction based on cycloplegic refraction.
In cases of anisometropia, spectacle adaptation alone may improve vision significantly.
Refractive correction should be worn consistently for 6–12 weeks before initiating occlusion therapy.

2. Occlusion Therapy (Patching)

The gold standard treatment for amblyopia. The dominant (sound) eye is patched to force use of the amblyopic eye.

Full-time patching: 6–8 hours/day for moderate to severe amblyopia
Part-time patching: 2–6 hours/day for mild to moderate amblyopia
May be combined with near tasks (drawing, puzzles, reading) to stimulate the amblyopic eye
Requires regular follow-up to monitor progress and prevent reverse amblyopia

3. Penalization Therapy

Penalization Therapy

Used when patching is not tolerated. The better-seeing eye is blurred with atropine drops or optical defocus.

Atropine 1% drops administered once daily in the dominant eye
Best for moderate amblyopia in compliant patients
Fewer compliance issues compared to patching

4. Vision Therapy

Vision Therapy

Includes structured visual activities designed to improve acuity, fixation, tracking, and binocular function.

Computerized programs, red-green anaglyphic activities, interactive games
Helps break suppression and promote binocular integration
Useful in both children and adults as adjunct to conventional therapy

5. Treatment of Underlying Causes

Removal of congenital cataracts, ptosis correction, or corneal scarring where present
Management of strabismus with glasses, vision therapy, or surgery

6. Pharmacological Approaches (Emerging)

Levodopa/carbidopa combinations and citicoline are being studied as neuro-enhancers
Still under clinical evaluation; not first-line therapy

Monitoring and Follow-up

Regular visits every 4–8 weeks during active therapy
Monitor visual acuity, compliance, ocular alignment, and stereopsis
Gradual weaning of patching to prevent recurrence
Relapses are common, especially in children <7 years; booster therapy may be needed

Prognosis

Excellent if treated early (before 5 years of age)
Moderate visual recovery possible in older children and even adults with new evidence of cortical plasticity
Better outcomes in anisometropic amblyopia than strabismic or deprivation types
Poor prognosis in deprivation amblyopia if not treated within the first few months of life

Recent Advances

Binocular therapy models: Dichoptic video games and movies to train fusion and visual balance
Digital platforms: Smartphone apps, virtual reality-based amblyopia training
Adult therapy programs: Showing promising results by leveraging residual neuroplasticity

Role of the Optometrist

Early screening and detection during school vision programs
Educating parents about compliance, patching, and the importance of follow-ups
Monitoring treatment response and adjusting therapy plans accordingly
Providing vision rehabilitation for residual amblyopia

Conclusion

Amblyopia is a major cause of preventable and treatable vision loss in children. Its close association with strabismus and refractive errors makes early screening essential. Timely intervention with optical correction, occlusion therapy, and supportive vision therapy can lead to remarkable visual improvements. With emerging digital tools and greater understanding of cortical plasticity, treatment of amblyopia is now extending beyond childhood. However, patient motivation and parental involvement remain the cornerstone of successful amblyopia management.

Nystagmus

Introduction:

Nystagmus is an involuntary, rhythmic oscillation of one or both eyes. These movements can be horizontal, vertical, torsional, or a combination of directions. Nystagmus may be physiological or pathological and can significantly impair vision, depth perception, and visual stability. It can be congenital or acquired, and its classification, causes, and management are essential areas of study in binocular vision and neuro-ophthalmology.

Definition

Nystagmus

Nystagmus is defined as a repetitive, uncontrolled movement of the eyes that can affect one or both eyes. It may occur spontaneously or be induced by visual or vestibular stimuli. The movement may be pendular (equal velocity in both directions) or jerk (faster in one direction, slower return phase).

Classification of Nystagmus

1. Based on Age of Onset:

Congenital (Infantile) Nystagmus: Appears in the first 6 months of life
Acquired Nystagmus: Develops later due to neurological, vestibular, or sensory causes

2. Based on Waveform:

Pendular: Equal velocity in both directions
Jerk: Slow drift in one direction followed by fast corrective saccade

3. Based on Direction:

Horizontal: Most common type (left-right movements)
Vertical: Up-down oscillations
Torsional: Rotatory movements around the visual axis
Mixed: Combination of directions

4. Based on Cause:

Sensory Defect Nystagmus: Caused by visual deprivation (e.g., congenital cataract, albinism)
Motor Defect Nystagmus: Idiopathic instability of ocular motor control
Latent/Manifest Latent Nystagmus: Common in patients with early-onset strabismus
Vestibular Nystagmus: Linked to inner ear dysfunction
Downbeat/Upbeat Nystagmus: Often associated with brainstem or cerebellar pathology

Etiology of Nystagmus

1. Congenital Causes:

Congenital idiopathic nystagmus
Albinism
Congenital cataract
Achromatopsia
Congenital optic nerve hypoplasia
Leber’s congenital amaurosis

2. Acquired Causes:

Multiple sclerosis
Brainstem or cerebellar lesions
Head trauma
Drug or alcohol intoxication
Vestibular disorders (e.g., Meniere’s disease, labyrinthitis)
Stroke or ischemia in the posterior circulation

Clinical Features

Oscillatory eye movements visible to examiner or reported as “shaky” vision (oscillopsia)
Head turn or tilt to adopt a null point (position where nystagmus dampens)
Reduced visual acuity, particularly in congenital types
Lack of stereopsis and poor binocular vision
Photophobia and poor contrast sensitivity in sensory forms

Important Terms

Null Point: Gaze position where nystagmus intensity is minimal and vision is best
Oscillopsia: Subjective perception of moving or bouncing visual environment (more common in acquired types)
Foveation Period: Time during which the eye remains relatively still and aligned with the object of regard

Diagnostic Evaluation

1. History:

Onset age, progression, associated symptoms
Presence of oscillopsia or head posture
History of trauma, neurological conditions, family history

2. Visual Acuity Testing:

Assess both near and distance acuity with and without null point
Check for improvement with eccentric viewing

3. Observation and Slit Lamp Examination:

Note direction, amplitude, frequency, and type of nystagmus
Look for associated anterior or posterior segment abnormalities

4. Ocular Motility and Gaze Testing:

Evaluate nystagmus in different gaze positions
Look for latent nystagmus (appears with monocular occlusion)

5. Neurological Assessment:

Rule out cerebellar or brainstem involvement
Evaluate balance, coordination, and cranial nerve function

6. Imaging:

CT or MRI may be necessary in acquired nystagmus to identify underlying lesions

Special Investigations

Electronystagmography (ENG): Measures eye movements and waveform characteristics
Video Nystagmography (VNG): Uses infrared cameras to record eye movements
Visual Evoked Potentials (VEP): To assess optic nerve and visual pathway function

Management of Nystagmus

1. Optical Correction:

Full refractive correction is essential
Contact lenses may offer improved vision due to stability during eye movements
Tinted lenses for photophobia in albinism or achromatopsia

2. Vision Therapy:

May help improve foveation, fixation stability, and binocular vision
Activities may include tracking, convergence exercises, and near-vision tasks
Helpful in functional adaptation and improving reading performance

3. Prisms:

Yoked prisms can shift the image into the null zone to reduce head turn
Base direction depends on the position of the null point
May improve comfort and posture in patients with head turn

4. Pharmacologic Treatment:

Baclofen, gabapentin, and memantine have shown benefit in acquired nystagmus
Limited role in congenital nystagmus
Trial should be monitored and tailored to individual response

5. Surgical Management:

Usually reserved for congenital types with head posture or significant oscillations. Options include:

Anderson-Kestenbaum Procedure: Muscle surgery to move eyes toward null point
Tenotomy and reattachment: Reduces nystagmus intensity and improves foveation
Can be combined with strabismus surgery in coexisting deviations

6. Low Vision Aids:

Magnifiers, CCTV, large-print reading materials
Useful in enhancing reading speed and visual functioning

Prognosis

Congenital nystagmus is typically non-progressive but rarely fully resolves
Vision can be stable or improve with age, especially if managed early
Acquired nystagmus may indicate serious underlying pathology and often affects visual stability
Oscillopsia may be disabling in acquired types, requiring long-term therapy

Role of the Optometrist

Early detection and differentiation between types of nystagmus
Comprehensive visual assessment and refractive correction
Prescription of yoked prisms or vision aids
Referral to neuro-ophthalmologist or neurologist when needed
Guidance on vocational and educational adjustments

Conclusion

Nystagmus is a complex ocular motor disorder that can significantly impact vision, daily functioning, and quality of life. Whether congenital or acquired, its evaluation requires a thorough understanding of ocular motility, neurological function, and binocular vision. Optometrists play a crucial role in early recognition, appropriate referrals, and visual rehabilitation. With a combination of optical, therapeutic, and sometimes surgical interventions, many patients with nystagmus can achieve improved comfort, function, and visual performance.

Non-Surgical Management of Squint

Introduction:

Squint, also known as strabismus, is a condition where the eyes are misaligned and point in different directions. One eye may turn in (esotropia), out (exotropia), up (hypertropia), or down (hypotropia) while the other eye looks straight ahead. Although surgery is a common treatment, there are several non-surgical approaches that are effective in certain cases, especially when initiated early. Non-surgical management is essential in controlling, reducing, or even eliminating the need for surgery in specific types of strabismus, particularly in accommodative and intermittent deviations.

Goals of Non-Surgical Management

To improve ocular alignment and reduce the angle of deviation
To promote and restore binocular vision and fusion
To eliminate or reduce suppression and diplopia
To manage underlying causes such as refractive errors or muscle imbalance
To provide cosmetic and functional improvement without surgical intervention

1. Optical Correction

The first and most important step in non-surgical management is accurate refraction and correction of refractive errors.

1.1 Full Cycloplegic Refraction

Especially important in children to uncover latent hypermetropia
Cyclopentolate or atropine is used for accurate measurement

1.2 Spectacle Correction

Prescribed based on cycloplegic results
Can correct esotropia caused by accommodative convergence
In anisometropia, correcting the unequal refractive status can reduce risk of amblyopia and facilitate binocular use

1.3 Bifocal or Progressive Lenses

In cases of accommodative esotropia with high accommodative-convergence/accommodation (AC/A) ratio
Provides additional plus power for near tasks, reducing the need for convergence

2. Prismatic Correction

Prisms are often used to align visual axes and help achieve binocular single vision (BSV) in small-angle deviations or in those not suitable for surgery.

Fresnel Prism

Fresnel Prisms: Temporary, stick-on prisms used to assess effectiveness before prescribing permanent ground-in prisms
Ground-in Prisms: Used in permanent corrections of small angle deviations
Base Direction: Determined by the direction of deviation (e.g., base out for esotropia, base in for exotropia)
Prisms are most effective in comitant deviations with fusion potential

3. Vision Therapy (Orthoptic Exercises)

Vision therapy involves a structured program of exercises designed to improve eye coordination, fusion, accommodative ability, and control of eye movements. It is especially useful in patients with intermittent squints, convergence insufficiency, and some forms of decompensated phorias.

3.1 Indications for Vision Therapy:

Intermittent exotropia with good control
Convergence insufficiency or excess
Divergence insufficiency or excess
Decompensating phorias
Post-surgical binocular therapy

3.2 Common Vision Therapy Exercises:

Brock String: Improves convergence and binocular control
Pencil Push-ups: Strengthens near convergence ability
Barrel Cards and Vectograms: Fusion training tools
Stereograms: Improve stereopsis and depth perception
Computerized Training: Interactive software and games like HTS, VTS4 used for engaging therapy

3.3 Benefits of Vision Therapy:

Improves eye coordination and visual comfort
Enhances suppression control and fusion ranges
Can reduce the frequency and duration of squint episodes

4. Amblyopia Treatment

Strabismic amblyopia must be managed alongside squint correction to ensure optimal visual development.

Occlusion Therapy: Patching of the dominant eye to stimulate the amblyopic eye
Penalization: Atropine drops in the dominant eye to blur near vision
Vision Exercises: Near work and visual stimulation for the amblyopic eye
Should be initiated before strabismus becomes long-standing and binocular vision is lost

5. Botulinum Toxin (Botox) Injection

Botulinum toxin A can be injected into extraocular muscles to temporarily weaken overacting muscles, allowing alignment to improve and fusion to develop. It is often used as an alternative to surgery in selected cases.

Botox Injection

Indications:

Small to moderate angle esotropia or exotropia
Infantile esotropia (as an early treatment)
Sixth nerve palsy (temporary realignment)

Advantages:

Minimally invasive, outpatient procedure
May restore alignment in early strabismus
Useful when surgery is not immediately possible

6. Management of Specific Non-Surgical Cases

6.1 Accommodative Esotropia:

Often fully correctable with glasses alone
Bifocals may be added if near deviation is greater than distance (high AC/A ratio)
Vision therapy may be used to enhance fusional reserves

6.2 Intermittent Exotropia:

May be controlled with vision therapy, especially in early stages
Exercises to improve convergence are essential
Prism therapy may be used temporarily

6.3 Vertical Deviations:

Prisms can help in small-angle deviations
Fusion training exercises to address vertical fusional reserves

6.4 Phorias:

Vision therapy is the primary treatment
Prisms may help with symptomatic decompensated phorias
Plus lenses may be used for convergence excess

7. Role of the Optometrist in Non-Surgical Management

Early detection through school screening and vision assessment
Comprehensive eye examination with refraction and binocular testing
Prescription of appropriate optical correction
Monitoring progress of amblyopia and binocular development
Designing and supervising orthoptic/vision therapy programs
Counseling patients and parents about the condition and management options

8. Limitations of Non-Surgical Management

May not fully correct large-angle deviations or congenital squint
Requires high patient motivation and compliance
Takes time and may not offer cosmetic results as quickly as surgery
Needs regular follow-ups to assess progress and adjust therapy

9. Patient Education and Counseling

Proper education plays a vital role in success:

Explain the condition and treatment goals clearly
Discuss importance of adherence to glasses and therapy routines
Set realistic expectations about treatment duration and results
Encourage supportive involvement from family members

Conclusion

Non-surgical management of squint offers a valuable alternative or complement to surgical correction, especially when implemented early and correctly. Accurate optical correction, vision therapy, prism adaptation, amblyopia treatment, and patient education form the backbone of this approach. For many types of strabismus, especially accommodative and intermittent forms, non-surgical methods can be highly effective in restoring binocular vision, reducing the angle of deviation, and improving both function and appearance. Optometrists play a key role in the diagnosis, therapy planning, and long-term management of patients undergoing non-surgical squint correction.

Restrictive Strabismus: Duane’s Syndrome, Brown’s Syndrome, and Congenital Fibrosis

Introduction:

Restrictive strabismus refers to ocular motility disorders where the eye movements are limited due to mechanical restrictions of the extraocular muscles or surrounding structures. Unlike paralytic squint, where muscle weakness causes limitation, restrictive types result from fibrosis, tightness, or abnormal innervation. The primary forms of congenital restrictive strabismus include Duane Retraction Syndrome (DRS), Brown’s Syndrome, and Congenital Fibrosis of the Extraocular Muscles (CFEOM). These conditions are important for optometrists and ophthalmologists to identify early, manage conservatively or surgically, and monitor throughout development.

1. Duane Retraction Syndrome (DRS)

Definition:

Duane Retraction Syndrome

Duane Retraction Syndrome is a congenital strabismus characterized by limited horizontal eye movement, globe retraction, and narrowing of the palpebral fissure on attempted adduction. It results from miswiring of cranial nerves, typically involving the absence of the abducens nerve (VI) and aberrant innervation of the lateral rectus by the oculomotor nerve (III).

Classification:

According to Huber's classification:

Type I: Limited abduction, normal or mildly limited adduction
Type II: Limited adduction, normal abduction
Type III: Limited abduction and adduction

Etiology:

Congenital absence or hypoplasia of the abducens nerve (CN VI)
Aberrant innervation of the lateral rectus by CN III
May be sporadic or familial; sometimes associated with syndromes (e.g., Goldenhar, Klippel-Feil)

Clinical Features:

Limited abduction and/or adduction depending on type
Globe retraction and narrowing of palpebral fissure during adduction
Upshoot or downshoot due to co-contraction
Abnormal head posture (face turn toward affected side)
Usually unilateral, left side more commonly affected
Binocular vision often present in primary position

Diagnosis:

Cover test and ductions show limited movement
Forced duction test shows resistance on adduction
Retraction of globe and palpebral fissure changes are key clinical signs
MRI may show absent abducens nerve

Management:

Observation: If primary position alignment is acceptable and binocular vision is intact
Glasses: For refractive errors and to improve fusion
Prism: Rarely used; limited utility in DRS
Surgery: Indicated for significant head turn, large deviations, or cosmetic concerns
Options include medial rectus recession, lateral rectus weakening, vertical rectus transposition

Prognosis:

Generally stable over time. Binocular vision often preserved, but full range of movement cannot be restored surgically. Proper education and monitoring are key.

2. Brown’s Syndrome

Definition:

Brown's Syndrome

Brown’s Syndrome is a restrictive strabismus characterized by limited elevation of the eye in adduction due to restriction or mechanical obstruction of the superior oblique tendon within the trochlea. It can be congenital or acquired.

Etiology:

Congenital: Short or inelastic superior oblique tendon or sheath
Acquired: Trauma, inflammation (e.g., sinusitis), surgery (e.g., glaucoma implants), rheumatoid arthritis

Clinical Features:

Restricted elevation in adduction (“pseudo-inferior oblique palsy”)
Normal elevation in abduction
Downshoot of eye in adduction
Positive forced duction test (resistance to elevation in adduction)
Absence of overaction of the contralateral inferior oblique
Head posture: Chin elevation or head tilt to maintain fusion
Often unilateral; bilateral in 5–10% of cases

Diagnosis:

Limitation of elevation in adduction on duction testing
Positive forced duction test confirms mechanical restriction
CT/MRI may be needed in acquired cases to assess for inflammation or mass lesions

Management:

Observation: Many congenital cases improve spontaneously over time
Prism therapy: For small deviations and head posture management
Surgical intervention: Indicated in symptomatic cases
Procedures include tenotomy or tenectomy of superior oblique tendon, or silicone spacer insertion
Caution: Post-operative superior oblique palsy or iatrogenic vertical deviation is possible

Prognosis:

Variable. Some cases resolve spontaneously; others require surgery. Recurrence or post-operative complications may occur and should be monitored long term.

3. Congenital Fibrosis of the Extraocular Muscles (CFEOM)

Definition:

Congenital Fibrosis of the Extraocular Muscles

Congenital Fibrosis of the Extraocular Muscles (CFEOM) is a rare non-progressive disorder characterized by congenital restrictive ophthalmoplegia and ptosis due to fibrosis of one or more extraocular muscles, usually from neurogenic origin. It represents a group of inherited ocular motility disorders.

Etiology and Genetics:

Autosomal dominant or recessive inheritance
Mutations in KIF21A, PHOX2A, and TUBB3 genes
Neurogenic origin with secondary muscle fibrosis

Classification:

Types of CFEOM:

CFEOM-1: Bilateral ptosis, infraducted globes (eyes fixed downward), absent upgaze
CFEOM-2: Bilateral ptosis and exotropia; oculomotor nerve hypoplasia
CFEOM-3: Variable presentation; may have some eye movements

Clinical Features:

Congenital ptosis (often severe)
Restricted ocular motility, especially in upgaze
Eyes fixed in downward or outward position
Head posture with chin elevation to compensate for ptosis and gaze limitations
Strabismus (often large-angle exotropia or hypotropia)
May have amblyopia due to ptosis or misalignment

Diagnosis:

History of congenital onset and family history of similar presentations
External ocular exam and motility testing
MRI of the orbits and brain may show small or absent cranial nerves and fibrotic muscles
Genetic testing can confirm subtype

Management:

Conservative Management: Includes refractive correction and amblyopia therapy
Ptosis Surgery: Frontalis suspension often required to lift eyelids
Strabismus Surgery: Challenging due to multiple tight or fibrotic muscles
Customized surgical plan based on individual motility pattern
Goals are to achieve acceptable head posture and primary position alignment, not full motility restoration

Prognosis:

Vision can be preserved with early intervention. Full eye movement cannot be achieved due to fibrotic and nerve-origin nature. Lifelong monitoring, refractive correction, and visual rehabilitation are essential.

Comparison Table

Feature	Duane’s Syndrome	Brown’s Syndrome	CFEOM
Onset	Congenital	Congenital or acquired	Congenital
Key Limitation	Abduction and/or adduction	Elevation in adduction	Severe global restriction
Head Posture	Face turn	Chin elevation	Chin elevation
Globe Retraction	Yes	No	No
Management	Observation or surgery	Observation or SO tenotomy	Complex surgical planning

Conclusion

Restrictive strabismus encompasses a group of complex, often congenital conditions that limit ocular motility due to mechanical or neural abnormalities. Duane’s Syndrome, Brown’s Syndrome, and CFEOM are the most significant restrictive strabismus disorders seen in clinical practice. Management requires a thorough understanding of the pathophysiology, careful diagnostic evaluation, and an individualized approach combining observation, optical correction, and sometimes surgery. While perfect alignment or full ocular motility may not always be achievable, early intervention can ensure optimal functional and cosmetic outcomes for the patient.

Surgical Management of Strabismus

Introduction:

Surgical management of strabismus involves the realignment of extraocular muscles to correct ocular deviations and restore binocular vision. It is commonly indicated when conservative approaches such as optical correction, prism therapy, or vision therapy fail to yield satisfactory results. Strabismus surgery can improve both visual function and cosmetic appearance, and it is one of the most frequently performed ophthalmic surgeries worldwide. A successful outcome requires accurate diagnosis, precise measurement of deviation, individualized surgical planning, and appropriate post-operative care.

Indications for Surgery

Constant or large-angle manifest deviations (tropias) affecting function or appearance
Failure of non-surgical management (e.g., glasses, prisms, vision therapy)
Unstable intermittent deviations causing asthenopia, diplopia, or fusion disruption
Head posture due to strabismus (e.g., face turn or chin elevation)
Associated with nystagmus null point (e.g., Kestenbaum procedure)
Cosmetic reasons or psychosocial concerns
To enable or enhance binocular fusion potential

Pre-operative Evaluation

Detailed history (onset, frequency, prior treatments, family history)
Assessment of visual acuity in both eyes, including amblyopia status
Measurement of deviation using prism cover test and alternate cover test at distance and near
Assessment of ocular motility to rule out restrictions or paralytic conditions
Evaluation of binocular function: fusion, stereopsis, and suppression tests
Examination for any underlying ocular or neurological pathology
Cycloplegic refraction to ensure refractive errors are addressed

Types of Surgical Procedures

Strabismus surgery involves altering the length, strength, or insertion of extraocular muscles. Depending on the deviation, different combinations of weakening (recession), strengthening (resection), or transposition procedures are performed.

1. Recession

Involves weakening a muscle by detaching it from its insertion and reattaching it further posteriorly on the sclera.

Reduces muscle pull
Commonly done on medial rectus in esotropia or lateral rectus in exotropia
Safe and widely used technique

2. Resection

Strengthening procedure where a segment of the muscle is removed (shortened), and the remaining muscle is reattached at the original insertion.

Increases muscle tension
Often performed on lateral rectus in exotropia or medial rectus in esotropia
Can be combined with recession of the antagonist muscle for balanced correction

3. Plication

A strengthening technique where the muscle is folded (without cutting) and sutured to its original insertion.

Preserves muscle integrity and blood supply
Quicker recovery and reversible if needed

4. Posterior Fixation (Faden Operation)

A suture is placed posterior to the insertion of the muscle, limiting its action in certain positions of gaze.

Useful in high AC/A ratio esotropia or nystagmus blockage syndrome
Does not affect primary position alignment significantly

5. Adjustable Suture Technique

Allows postoperative adjustment of muscle position for fine-tuning alignment.

Common in adults and cooperative older children
Minimizes undercorrection or overcorrection
Adjustment done within 24 hours postoperatively

6. Transposition Procedures

Used in cases of paralytic strabismus or absence of muscle function (e.g., sixth nerve palsy, Duane’s syndrome).

Vertical rectus muscles are repositioned to substitute for horizontal recti
Examples: Hummelsheim, Jensen, or full-tendon transpositions

Surgical Techniques Based on Type of Deviation

1. Esotropia (Inward Deviation)

Bilateral medial rectus recession for large-angle esotropia
Unilateral recession-resection (medial rectus recession + lateral rectus resection) in moderate angles
Faden operation in high AC/A ratio accommodative esotropia

2. Exotropia (Outward Deviation)

Bilateral lateral rectus recession for basic exotropia
Unilateral lateral rectus recession and medial rectus resection in small to moderate deviations
Variable strategies based on control, frequency, and angle of deviation

3. Vertical Strabismus

Superior or inferior rectus recession for vertical deviations
Oblique muscle surgery for cyclovertical deviations (IO weakening in inferior oblique overaction)

4. Paralytic Strabismus

Transposition procedures (e.g., full-tendon VRT for sixth nerve palsy)
Botulinum toxin injections as a temporary or adjunct measure
Goal is to restore alignment and reduce diplopia in primary position

5. Restrictive Strabismus

Requires pre-operative forced duction test
Surgery tailored to relieve mechanical restrictions (e.g., SO tenotomy in Brown’s syndrome)
May involve muscle recession or removal of scar tissue

Intraoperative Considerations

Standard aseptic techniques in operating room
Use of limbal or fornix-based conjunctival incisions
Scleral fixation of muscle using absorbable or non-absorbable sutures
Gentle tissue handling to avoid postoperative fibrosis
Muscle positioning using adjustable sutures if planned

Postoperative Care

Topical antibiotics and steroid drops for 1–2 weeks
Cold compresses for edema
Follow-up on day 1, 1 week, and at 4–6 weeks
Visual acuity, ocular alignment, and motility assessments
Monitor for complications such as overcorrection, undercorrection, or infection
Amblyopia therapy resumed if needed

Complications of Strabismus Surgery

Overcorrection or undercorrection of deviation
Scleral perforation (rare)
Infection or endophthalmitis (rare)
Anterior segment ischemia (especially in multiple rectus surgeries)
Slipped or lost muscle
Adherence syndrome or fibrosis
Persistent diplopia in adult patients

Outcome and Prognosis

Success rates vary from 60–90% depending on the case and surgical plan
Best outcomes seen in comitant deviations with good binocular potential
Some patients may need re-operation or prism correction post-surgery
Improvement in cosmesis and head posture is often dramatic
Long-term follow-up essential for amblyopia, binocular vision, and residual deviations

Recent Advances

Minimally Invasive Strabismus Surgery (MISS): Uses small incisions and microinstruments to reduce trauma
Adjustable Suture Enhancements: For greater precision and patient-customized alignment
Navigation-assisted strabismus surgery: Under research to improve anatomical accuracy
Combined botulinum toxin and surgery: For complex or re-operation cases

Role of the Optometrist in Surgical Management

Preoperative detection and referral for surgical assessment
Measuring and documenting ocular deviation and binocular status
Patient education about surgical risks and expectations
Postoperative follow-up, including refraction, amblyopia therapy, and prism prescription if required
Coordinating vision therapy to maintain or regain fusion post-surgery

Conclusion

Surgical management plays a critical role in correcting strabismus when conservative treatments are insufficient. The procedure is highly individualized, considering the type, frequency, and severity of deviation, binocular vision potential, and cosmetic concerns. With advances in surgical techniques and improved pre- and post-operative care, most patients can achieve excellent functional and cosmetic outcomes. The collaboration between ophthalmic surgeons and optometrists ensures that surgical intervention is appropriately timed, executed, and followed up with rehabilitative support to maximize visual success.

For more parts of Binocular Vision II 👇

👉 Part I

👉 Part II