Squint

 

🔹 What is Squint?

• Squint (medical term: strabismus) is a condition where the eyes are not aligned properly.

• One eye may look straight ahead while the other turns inwards, outwards, upwards, or downwards.

🔹 Types of Squint

1. Esotropia – Eye turns inward (cross-eye).

2. Exotropia – Eye turns outward (wall-eye).

3. Hypertropia – Eye turns upward.

4. Hypotropia – Eye turns downward.

🔹 Based on Onset

• Congenital (Infantile) Squint – Present at birth or develops in first 6 months.

🔹 What is Congenital (Infantile) Squint?

• A squint (strabismus) that is present at birth or develops within the first 6 months of life.

• Most commonly, it is an esotropia (eye turning inward).

🔹 Causes

• Exact cause often unknown (idiopathic).

• Can be due to:

• Poor development of binocular vision in infancy.

• Imbalance of extraocular muscles.

• Strong family history of squint.

• Sometimes associated with neurological or developmental problems.

🔹 Features

• Usually large, constant deviation (eye turn).

• Infant cannot develop normal binocular single vision.

• May lead to amblyopia (lazy eye) if not treated early.

• Abnormal head posture sometimes seen (child may tilt or turn head to compensate).

✨ Interesting fact: Some babies look cross-eyed in the first 3–4 months due to a broad nasal bridge (“pseudo-squint”), but this is normal and usually disappears as the face develops. True congenital squint persists beyond 6 months.

• Acquired Squint – Appears later in childhood or adulthood.

🔹 What is Acquired Squint?

• A squint that appears after 6 months of age (in childhood or adulthood).

• Unlike congenital squint, acquired forms often cause double vision (diplopia) because the brain is already used to seeing with both eyes.

🔹 Causes

1. Refractive Errors

   • Uncorrected hyperopia (farsightedness) → can lead to accommodative esotropia.

2. Nerve Palsies

   • Paralysis of eye muscles due to trauma, diabetes, hypertension, or neurological disease.

3. Sensory Squint

   • If one eye loses vision (cataract, corneal opacity, retinal disease), it may drift (eso- or exotropia).

4. Decompensated Squint

• A previously minor/hidden squint (phoria) becomes noticeable due to stress, illness, or fatigue.

🔹 Features

• Sudden or gradual onset after infancy.

• May present with:

  • Double vision (diplopia)

  • Abnormal head posture (tilt or turn to reduce diplopia)

  • Cosmetic misalignment.

• Unlike congenital squint, amblyopia is less common (except in children).

🔹 Types of Acquired Squint

1. Accommodative Esotropia – due to uncorrected hyperopia.

2. Paralytic Squint – due to cranial nerve palsy (III, IV, or VI).

3. Sensory Squint – due to poor vision in one eye.

4. Consecutive Squint – appears after squint surgery (over/undercorrection).

🔹 Treatment

• Glasses (for refractive errors, especially accommodative squint).

• Prisms (to help with double vision).

• Eye exercises (orthoptics) for small squints or convergence problems.

• Surgery on eye muscles for large or persistent squints.

• Treat underlying cause (nerve palsy, cataract, etc.).

✨ Interesting fact: Adults who suddenly develop a squint often notice troublesome double vision, whereas children’s brains may suppress the image from the deviating eye (leading to amblyopia instead).

🔹 Based on Occurrence

• Constant Squint – Present all the time.

🔹 What is Constant Squint?

• A type of squint where one eye is always deviated, without any period of straight alignment.

• More common in children than adults.

• Often leads to amblyopia (lazy eye) if untreated.

Causes

1. Congenital / Infantile Squint – present from birth or early infancy.

2. Uncorrected refractive error – especially high hyperopia.

3. Sensory deprivation – poor vision in one eye (cataract, corneal opacity, retinal disease).

4. Muscle imbalance – weakness/overaction of extraocular muscles.

🔹 Features

• Eye is always misaligned (eso-, exo-, hyper-, or hypotropia).

• No alternation: Usually one eye is straight, and the other is always deviated.

• Amblyopia common in the deviated eye (because the brain ignores its image).

• Abnormal head posture may be present (child may tilt/turn head).

🔹 Types of Constant Squint

• Unilateral Constant Squint – always the same eye deviates.

• Alternating Constant Squint – eyes take turns deviating, so amblyopia risk is lower.

✨ Interesting fact: Constant squint is one of the main causes of lazy eye in children—which is why early eye screening (before age 5–6 years) is very important.

• Intermittent Squint – Comes and goes (often worse when tired).

🔹 What is Intermittent Squint?

• A type of squint where the eye deviates only sometimes and is straight at other times.

• The eye alignment may be normal when the child is rested, concentrating, or indoors, but the deviation shows up when tired, sick, or looking at distant objects.

🔹 Causes

1. Muscle imbalance – weakness of eye muscles controlling alignment.

2. Refractive error – uncorrected vision problem.

3. Fatigue or illness – causes eye control to break down.

4. Decompensated phoria – a hidden squint (phoria) becomes visible intermittently.

🔹 Features

• Squint is not constant – appears occasionally.

• Often worse when:

  • Looking far away (distance exotropia).

  • Daydreaming, tired, or sick.

  • In bright sunlight (children may close one eye outdoors).

• Diplopia (double vision) may occur in adults; children usually suppress one eye to avoid it.

• Amblyopia (lazy eye) is less common than in constant squint, because eyes are straight part of the time.

🔹 Types of Intermittent Squint

• Intermittent Exotropia – most common, eyes drift outward occasionally.

• Intermittent Esotropia – eyes sometimes turn inward.

🔹 Treatment

1. Glasses – if refractive error is present.

2. Orthoptic exercises – to strengthen binocular control.

3. Prisms – for symptomatic diplopia in older patients.

4. Surgery – if deviation is large or control is poor.

5. Observation – if mild and well-controlled (no amblyopia/diplopia).

✨ Interesting fact: Intermittent squint is sometimes called “phoria–tropia” because the eye shifts between a latent squint (hidden) and a manifest squint (visible).

🔹 Based on Alternation

Alternating Squint – Both eyes take turns deviating.

🔹 What is Alternating Squint?

• A type of squint where both eyes take turns deviating.

• Example: Sometimes the right eye turns in/out, sometimes the left eye turns in/out.

• The brain alternates fixation between the two eyes.

🔹 Causes

• Often due to muscle imbalance without one eye being much weaker than the other.

• Can develop from untreated refractive error.

• May follow congenital or acquired squint if both eyes remain functional.

🔹 Features

• Deviation alternates between the two eyes (not fixed to one side).

• Amblyopia is rare, because each eye gets a chance to fixate → vision in both eyes is usually maintained.

• May still cause poor binocular vision (depth perception affected).

• Cosmetic misalignment visible.

🔹 Types of Alternating Squint

• Alternating Esotropia – eyes alternately turn inward.

• Alternating Exotropia – eyes alternately turn outward.

• Alternating Vertical Squint – one eye turns up/down alternately.

🔹 Treatment

Glasses – to correct refractive error.

Orthoptic exercises – to improve binocular coordination.

Surgery – to realign eyes if deviation is large or cosmetically significant.

Observation – if mild and no amblyopia present.

✨ Interesting fact: Alternating squint is often less harmful than unilateral constant squint, because both eyes remain strong and do not develop amblyopia.

Unilateral Squint

🔹 What is Unilateral Squint?

• A type of squint where the same eye always deviates, while the other eye always fixates (looks straight).

• Opposite of alternating squint, where the eyes take turns.

🔹 Causes

• Congenital muscle imbalance.

• Uncorrected refractive error (especially hyperopia).

• Sensory deprivation – poor vision in one eye due to cataract, corneal opacity, or retinal disease.

• Often seen in children with congenital or early-onset squint.

🔹 Features

• The same eye is always turned (eso-, exo-, hyper- or hypotropia).

• High risk of amblyopia (lazy eye) in the deviated eye because the brain suppresses its image.

• No alternation → the fixing eye stays strong, while the deviating eye becomes weaker.

• Binocular vision (depth perception) is usually poor or absent.

🔹 Types

• Unilateral Esotropia – one eye always turns inward.

• Unilateral Exotropia – one eye always turns outward.

• Unilateral Vertical Squint – one eye always turns upward/downward.

🔹 Treatment

1. Correct refractive error (glasses/contact lenses).

2. Amblyopia therapy – patching the good eye to stimulate the deviated eye.

3. Surgery – to realign the squinting eye.

4. Vision therapy/orthoptic exercises – to strengthen binocular vision if possible.

✨ Interesting fact:
Unilateral squint is more harmful than alternating squint, because amblyopia is very common if not treated early (especially in children under 7 years).

🔹 Based on Cause

1. Paralytic Squint – Due to weakness or paralysis of an eye muscle (nerve palsy).

🔹 What is Paralytic Squint?

• A type of squint caused by paralysis or weakness of one or more extraocular muscles (or the nerves supplying them).

• The affected eye cannot move fully in the direction of the weak muscle.

• More common in adults than children.

🔹 Causes

1. Cranial Nerve Palsy

   • 3rd nerve (oculomotor) → multiple muscles affected.

   • 4th nerve (trochlear) → superior oblique affected.

   • 6th nerve (abducens) → lateral rectus affected.

2. Trauma – orbital or head injury.

3. Vascular diseases – diabetes, hypertension, stroke.

4. Neurological disorders – multiple sclerosis, brain tumor.

5. Infections – meningitis, viral illness.

🔹 Features

• Restricted eye movement in the direction of the weak muscle.

• Diplopia (double vision) – especially in adults.

• Abnormal head posture – patient may tilt or turn head to reduce diplopia.

• Secondary deviation (when fixing with affected eye, deviation appears larger).

• Often sudden onset (after nerve palsy or trauma).

🔹 Differences from Non-Paralytic (Concomitant) Squint

• In paralytic squint → amount of deviation changes with gaze direction.

• In concomitant squint → deviation remains the same in all directions.

🔹 Treatment

1. Treat underlying cause (e.g., control diabetes, treat infection, manage trauma).

2. Prisms in glasses – to reduce diplopia.

3. Occlusion (patching one eye) – for severe double vision.

4. Botulinum toxin injection – temporary muscle balance.

5. Squint surgery – for persistent cases after 6–12 months.

✨ Interesting fact:
Patients with 6th nerve palsy (lateral rectus weakness) often turn their head toward the affected side to reduce double vision — a classic clinical sign.

1. Non-paralytic (Concomitant) Squint – Eye muscles work normally but alignment is off; the degree of squint remains the same in all directions of gaze.

What is it?

• A type of squint where the degree of deviation is the same in all directions of gaze.

• Eye muscles and their nerve supply are normal, but the coordination between the two eyes is faulty.

• Most common form of squint in children.

🔹 Causes

• Refractive errors (especially uncorrected hyperopia → accommodative esotropia).

• Congenital imbalance of eye muscle coordination.

• Family history of squint.

• Sometimes develops after illness, stress, or fatigue in children predisposed to eye misalignment.

🔹 Features

• Equal deviation in all gaze directions (hence concomitant).

• Full eye movements are present (unlike paralytic squint).

• May be constant or intermittent.

• Can be unilateral (same eye deviates) or alternating (eyes take turns).

• Diplopia (double vision) usually absent in children because the brain suppresses one image.

• High risk of amblyopia (lazy eye) if unilateral and constant.

🔹 Types

1. Accommodative Squint – due to uncorrected hyperopia.

2. Non-accommodative Squint – unrelated to glasses prescription.

3. Partially accommodative Squint – glasses reduce but don’t fully correct the squint.

🔹 Treatment

1. Glasses – to correct refractive error (especially hyperopia).

2. Amblyopia therapy – patching the good eye to strengthen the weaker eye.

3. Orthoptic (vision) exercises – to improve binocular vision.

4. Squint surgery – if glasses/therapy cannot fully align the eyes.

✨ Interesting fact:
Unlike paralytic squint, in non-paralytic squint the angle of deviation is the same in all gaze directions — a key point for diagnosis in clinics.

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