Squint: it is not something a child grows out of

Strabismus, or squint, is a misalignment of the eyes: one looks at the target while the other turns in, out, up or down. It affects a few per cent of children.

The advice most often given to parents — that the child will grow out of it — is correct only for the first few months of life, when intermittent misalignment is normal as the visual system settles. Beyond about four months, a persistent or intermittent squint needs assessing.

Why it matters beyond appearance

The cosmetic concern is real and should not be dismissed; children with a visible squint are teased, and it affects confidence through school and beyond. But there are two functional consequences that matter more.

Amblyopia. When the eyes point in different directions the brain receives two incompatible images. In a young child the brain suppresses one — and a suppressed eye does not develop its connection to the brain. Vision in that eye is then permanently reduced, regardless of whether the alignment is later corrected.

Loss of binocular vision. Depth perception depends on the brain fusing two slightly different views. A child whose eyes never work together does not develop it, which affects judgement of distance — catching, pouring, driving, and a range of practical and sporting tasks.

Both consequences are time-sensitive. The visual system's plasticity declines through childhood, and treatment started at three achieves results that treatment started at nine does not.

The kind that looks like a squint and is not

Many infants, particularly with a wide nasal bridge and prominent epicanthic folds, appear to have an inward-turning eye when they do not. The folds cover more of the white on the inner side and create the impression.

This is pseudostrabismus, and it resolves as the face grows. It is distinguished from a real squint in a moment by a practitioner — the reflection of a light in each pupil is symmetrical in pseudostrabismus and is not in a genuine squint. It is worth having checked rather than assumed, in either direction.

Causes

Often the muscle balance or the neural control of alignment. But a very common and highly treatable cause is uncorrected long-sightedness: the child over-focuses to see clearly, and the focusing effort drags the eyes inward. This form — accommodative esotropia — frequently straightens with spectacles alone, which is a good reason for an examination before anything else is contemplated.

Less commonly a squint signals something that needs urgent attention: a cataract, a retinal problem, or a nerve palsy. A squint that appears suddenly, particularly with double vision, a head tilt or headache, should be assessed promptly rather than routinely.

Treatment

Spectacles first, where a refractive error is driving it. Treatment of any associated amblyopia, usually by patching. Surgery to the eye muscles where alignment does not resolve optically — effective, and sometimes needing more than one procedure. Vision therapy for specific convergence problems. Botulinum toxin in selected cases.

The order matters: correcting the vision and the refractive error comes before considering surgery, because a proportion of squints do not need it once the child can see properly.

In adults

An adult squint may be long-standing or may be new. A new squint in an adult, particularly with double vision, is a medical matter and needs prompt assessment — it can indicate a nerve palsy, thyroid eye disease, or a neurological cause.

A long-standing squint in an adult can still be treated surgically. It is often assumed to be too late; it is not. The vision in an amblyopic eye will not recover, but alignment can be restored, and for many adults the effect on confidence and on how they are perceived is substantial.

What to do

If a child's eye turns — constantly, intermittently, or only when tired — have it examined. If in doubt, photographs taken with a flash, straight on, are useful evidence: an asymmetric reflection in the pupils is worth showing the practitioner.