Strabismus (Squint)

What is Strabismus (Squint)?

Strabismus — commonly called a squint — is a condition in which the two eyes are not aligned and do not point in the same direction simultaneously. One eye may turn inwards (esotropia), outwards (exotropia), upwards (hypertropia), or downwards (hypotropia). It affects approximately 3% of children and is also common in adults, arising from nerve palsy, thyroid eye disease, or decompensation of a previously controlled childhood squint. Strabismus can cause amblyopia in children and double vision in adults, and is treated medically or surgically.

Symptoms

• Visible eye misalignment — one eye appears to turn in, out, or vertically
• Double vision (diplopia) — more common in adults with acquired squint
• Head tilt or turn to control double vision
• Closing or covering one eye to eliminate double vision
• Poor depth perception
• In children — amblyopia, or the child does not appear to notice double vision due to suppression

Causes

• Childhood esotropia — accommodative esotropia (related to hyperopia), infantile esotropia
• Nerve palsy — third, fourth, or sixth cranial nerve
• Thyroid eye disease (Graves' ophthalmopathy) causing restrictive squint
• Decompensated phoria — a previously controlled tendency to squint breaking down with fatigue, illness, or age
• Mechanical restriction — following trauma, orbital fracture, previous surgery

Diagnosis

Orthoptic assessment: cover test, prism cover test, ocular motility examination, assessment of binocular function and diplopia. Neuroimaging where nerve palsy is suspected.

Treatment

Glasses may fully correct an accommodative esotropia. Prisms can neutralise diplopia in selected patients. Botulinum toxin (Botox) injections into the extraocular muscles may be used as primary treatment or pre-operatively. Surgical realignment of the eye muscles (recession and/or resection) is the definitive treatment for most forms of strabismus.