Squint refers to misalignment of the eyes. It is also known as strabismus. When the eyes are not aligned, the images on the retina do not match. This can cause double vision, although the brain often compensates to prevent this.
The brain may favour one eye and reduce input from the other, leading to that eye becoming weaker. If this is not treated, the weaker eye does not develop normal vision, leading to a permanent reduction in vision (amblyopia).
Concomitant squints are due to problems with how the eyes are controlled and how they work together, rather than a problem with the eye muscles themselves. The degree of deviation will be equal during eye movements in all directions.
Paralytic squints are uncommon in children and are more often seen in adults. They are due to paralysis in one or more of the extraocular muscles. The degree of deviation will vary when the eyes are moved in different directions.
Definitions
- Strabismus: the eyes are misaligned
- Amblyopia: the affected eye has reduced vision compared with the stronger eye
- Esotropia: inward-positioned squint (affected eye towards the nose)
- Exotropia: outward-positioned squint (affected eye towards the ear)
- Hypertropia: upward drifting affected eye
- Hypotropia: downward drifting affected eye
Causes
Cases of squint in otherwise healthy children are usually idiopathic, meaning there is no underlying cause. Causes of squint include:
- Hydrocephalus
- Cerebral palsy
- Space-occupying lesions (e.g., retinoblastoma)
- Trauma
Examination
Basic examination steps include:
- General inspection
- Eye movements
- Visual acuity
- Red reflex and fundoscopy (screening for retinoblastoma, cataracts, and other retinal pathology)
Hirschberg’s Test
Shine a pen torch at the patient from 1 metre away. When they look at it, observe the reflection of the light source on their cornea. The reflection should be central and symmetrical. A deviation from the centre indicates a squint. Make a note of the affected eye and the direction the eye deviates.
Cover Test
Cover one eye and ask the patient to focus on an object in front of them. Move the cover across to the opposite eye and watch the movement of the previously covered eye. If this eye moves inwards, it means it had drifted outwards when covered (exotropia). If it moves outwards, it means it had drifted inwards when covered (esotropia).
Management
Intermittent eye misalignment in children under 3 months is common and often resolves without treatment. Constant misalignment or squint in children over 3 months of age require specialist assessment and management.
Treatment needs to be started early, particularly before age 8, when visual development slows. Delayed treatment increases the risk of permanent reduction in vision, even if the eye position is corrected later.
An occlusive patch can be used to cover the stronger eye and force the weaker eye to develop. An alternative to the patch is atropine drops in the good eye, blurring the vision in that eye.
An ophthalmologist coordinates management. It is essential to treat any underlying pathology, such as cataracts. Refractive errors can be corrected with lenses.
Last updated January 2026
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