Strabismus: what it is, types and causes

Strabismus is when the eyes look in different directions: one straight ahead, while the other turns inward, outward, up or down. You can notice it in a photo or during a conversation — sometimes the eye crosses constantly, and sometimes only at certain moments. Let's look at what causes it and when a visit to the doctor should not be delayed.

What strabismus is and how it looks

Each eye is surrounded by six muscles, and they work as a team: they aim both eyes at a single object. With strabismus the team is out of sync — one eye looks at the object, the other drifts to the side and looks at something else.

Two different images arrive in the brain. In children the brain quickly learns to ignore the picture from the weaker eye — this is how amblyopia, the "lazy eye", develops. Without treatment this eye will not start to see well. It can also happen the other way round: a lazy eye appears first and brings strabismus with it.

What it looks like: you look at a family photo where everyone is looking at the camera, and you see that one person's pupil is shifted toward the bridge of the nose, and the head is slightly turned.

A quick check with an attentive look is not a diagnosis, but a way to notice changes over time: you can look through several recent photos where the person is looking straight at the camera and observe whether they tilt their head to one side or cover one eye when looking into the distance. Such habits are exactly the kind of signal that it is time to have vision checked.

Types of strabismus

The type is easiest to describe by where the eye turns:

• inward, toward the nose — esotropia, the most common variant;
• outward, toward the temple;
• upward;
• downward.

The second dimension is when it appeared: some people are born with strabismus, some acquire it later. In most children with an unclear cause, the problem is present at birth or soon after.

Why the eye started to cross: causes

The exact cause is not always known, and usually it is a matter of muscle control rather than muscle strength. Heredity is a risk factor: strabismus can run in families.

In children the eye often crosses because it is trying to cope with a vision problem: myopia, hyperopia, astigmatism. Less often the causes are different: certain infections, for example measles, genetic syndromes, developmental delays, cerebral palsy, other problems of the brain and nerves. Strabismus can also be a symptom of a rare childhood eye tumor — retinoblastoma — which is why a child is shown to a doctor.

In adults strabismus appears against a background of diabetes, thyroid disease, Guillain-Barré syndrome, injury to the eye or head, stroke, botulism, after loss of vision due to illness or damage to the eye.

Constant and intermittent strabismus: when the eyes cross sometimes

Strabismus can be constant or intermittent. In infants under 3 months, occasional strabismus is common and usually does not worry doctors. If the child is older than 3 months and the eye periodically crosses, that is a reason to see a specialist — as is constant strabismus at any age.

In adults, a separate reason to come for an appointment is newly appeared strabismus or double vision. Children, by the way, often do not complain of double vision: the brain suppresses the picture too quickly.

How strabismus is diagnosed

The doctor examines the eyes and performs tests that show the degree of misalignment: corneal light reflex, cover-uncover test, examination of the retina, a standard ophthalmological examination, and a visual acuity check. A neurological examination is sometimes added.

A referral for a consultation can come from a family doctor or an optician where you had your vision checked. A photo on your phone is a useful clue, but not a substitute for an examination.

Why strabismus is dangerous and when a doctor is needed

Without correction the consequences accumulate: persistent blurred or double vision, lazy eye, and in children — awkwardness and reduced self-esteem. About a third of children with strabismus develop amblyopia, and without treatment, up to about age 11, vision loss can become permanent. Even after successful treatment, strabismus and amblyopia often return, so monitoring continues.

You should see a doctor if a child's eye crosses constantly; if the child is older than 3 months and the strabismus is intermittent; if they tilt their head to one side or close one eye when looking at objects; if strabismus or double vision has appeared in an adult.

Strabismus by itself is not a reason to call an ambulance. 103/112 — if the eye suddenly turned or double vision appeared after a head injury or together with a suspected stroke.

This material is for reference: it helps you get your bearings and ask the doctor the right questions, but it does not replace a consultation with a specialist.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer