Strabismus (Squint)
Symptoms, causes, treatment, and when to see an optician
Overview
Strabismus, commonly known as a squint or crossed eyes, is a condition in which the eyes do not align properly — one eye may turn inward, outward, upward, or downward while the other looks straight ahead. Squint is relatively common in children, affecting approximately 2-3% of the UK population. If left untreated in childhood, it can lead to amblyopia (lazy eye) and permanent loss of binocular vision. However, squint can also develop in adults, sometimes as a sign of an underlying condition requiring investigation.
Symptoms
- One eye turning inward (convergent or esotropia), outward (divergent or exotropia), upward, or downward
- The turn may be constant or intermittent — appearing only when the child is tired, unwell, or focusing at near distances
- Double vision (more common in adults who develop a new squint)
- Closing or covering one eye in bright sunlight or when concentrating
- Abnormal head posture — tilting or turning the head to compensate
- In children: poor depth perception and difficulty with hand-eye coordination
- An infant whose eyes are not straight after 3 months of age
Causes & Risk Factors
- Imbalance in the muscles controlling eye movement
- Uncorrected refractive error, particularly hyperopia (long-sightedness) — the effort of focusing can trigger the eyes to turn inward
- Family history of squint or amblyopia
- Premature birth or low birth weight
- Conditions affecting the brain or nerves controlling eye muscles — such as cerebral palsy, Down syndrome, or head injury
- In adults: cranial nerve palsy, stroke, thyroid eye disease, diabetes, or myasthenia gravis
Treatment Options
Treatment for childhood squint depends on the cause and severity and should begin as early as possible for the best outcome. If an uncorrected refractive error is contributing, glasses are the first step — in many cases of accommodative esotropia (where hyperopia is pulling the eyes inward), glasses alone can straighten the eyes. If amblyopia (lazy eye) has developed, patching therapy — covering the stronger eye to strengthen the weaker one — is the standard NHS treatment, usually for several hours a day over weeks or months.
If glasses and patching do not fully correct the squint, surgery on the eye muscles may be recommended. Squint surgery is performed under general anaesthetic in children and is available on the NHS. The operation adjusts the tension or position of one or more of the muscles that control eye movement. In many cases, one operation is sufficient, but some children require further adjustment. Botulinum toxin (Botox) injections into the eye muscles are an alternative used in some types of squint, particularly in adults.
In adults, a new squint always warrants investigation to rule out underlying conditions such as cranial nerve palsy, stroke, thyroid eye disease, or intracranial pathology. Treatment depends on the cause: prisms in glasses can compensate for double vision, and squint surgery or botulinum toxin injections may be appropriate once the underlying condition is stable. Orthoptic exercises may help in certain types of intermittent squint. If you or your child has a squint, prompt assessment by an optometrist is essential — early treatment gives the best chance of achieving good vision in both eyes.
Prevention Tips
- Have children's eyes tested from age three — earlier if you notice a squint or have a family history
- Ensure children wear their prescribed glasses consistently, especially if prescribed for hyperopia
- Attend all follow-up and patching appointments to prevent amblyopia
- In adults, manage underlying conditions (diabetes, thyroid disease) that may contribute to squint
- If a new squint develops suddenly in an adult, seek urgent medical attention
When to See an Optician
Book an eye test urgently if you notice a child's eye turning in any direction, or if an adult develops new double vision or a squint — early assessment and treatment are critical for the best visual outcome.
Key Facts
- Category
- Common condition
- Typically Affects
- Most commonly diagnosed in children under 5, but can develop at any age
- Key Symptoms
- 7 identified symptoms
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Detecting Strabismus (Squint)
The following eye tests can help detect signs of strabismus (squint):
- Standard eye test
- OCT retinal scan
- Visual field test
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