What is a squint?
A squint is a condition where the eyes are misaligned. Whilst one eye looks straight ahead, the other eye turns to point inwards, outwards, upwards or downwards. Squints are common, and affect about 1 in 20 children.
Most squints develop before preschool age, usually by the time a child is three years old. The movement of each eye is controlled by six muscles that pull the eye in specific directions.:
The lateral rectus muscle pulls the eye outwards towards the ear.- The medial rectus muscle pulls the eye inwards towards the nose.
- The superior rectus muscle is mainly responsible for upwards movements.
- The inferior rectus muscle mostly pulls the eye downwards.
- The superior and inferior oblique muscles help to stabilise the eye movements
- particularly for looking downwards and inwards, or upward and outward movements.
What types of squint are there?
Squints are described by the direction of the squinting (turning) eye:
- Exotropia (divergent squint): the squinting eye turns out
- Esotropia (convergent squint): the squinting eye turns in
- Hypertropia / hypotropia (vertical squint): the squinting eye turns up / down
They are also described by how well the squint is controlled:
- A latent squint is one where the child is able to control the squint most of the time
but it becomes apparent under certain circumstances e.g. when tired or in bright sunshine (you may notice your child closing one eye). - A manifest squint is one where the eyes are visibly misaligned.
What causes a squint?
- Refractive error: refraction is the bending of light by the eye to produce a focussed image of what it sees.
Many children develop a squint because they need glasses.
A convergent squint will commonly occur in long (far) sighted children when they are 1-3 years of age.
This occurs because of their attempts to focus which causes the eyes to over-converge. Early detection and glasses correction can prevent the squint and the development of amblyopia (lazy eye). - Poor vision: if the vision is poor in both eyes due to a significant refractive error or a structural problem with the eye(s), a squint will often develop.
- Infantile squints: sometimes a misalignment can happen in the first 6 months of life.
Often there is no reason found for this, but there may be a family disposition.
Children with cerebral palsy and syndromes like Down’s syndrome are also at higher risk. - Neurological problems: occasionally a squint may develop due to a fault with one of the 3 cranial nerves responsible for eye movement. This type of squint is often accompanied by double vision and usually requires further investigation.
More information on squints can be found here.