Strabismus and Amblyopia (Lazy Eye): Signs, Treatment, Options

Strabismus, often called a squint or crossed eyes, means the eyes do not point in the same direction. Amblyopia, commonly known as lazy eye, means the vision in one eye (or occasionally both) has not developed normally during childhood, even with the best glasses, because the brain has learned to favour the other eye. The two conditions are closely linked: a turned eye is one of the main causes of amblyopia, and both are among the most common eye problems in children.

The most important message for parents is that timing matters. The visual system is most adaptable in early childhood, so amblyopia found and treated early responds best. This guide explains the types of strabismus and amblyopia, how they are detected, and the full range of treatments, from glasses and patching to surgery, newer binocular digital therapies, and what can still be done for older children and adults.

What is strabismus?

Six small muscles move each eye. They must work in perfect coordination so both eyes aim at the same target and the brain can merge the two images into one three-dimensional picture. In strabismus, this coordination fails and one eye turns in, out, up or down, either all the time (constant) or only sometimes (intermittent), for example when tired, ill or looking far away.

In accommodative esotropia, a long-sighted child focuses hard to see clearly, and because focusing and turning the eyes inwards are linked, one eye turns in. Glasses that correct the long-sightedness can straighten the eyes completely in many of these children.

Pseudostrabismus: when the eyes only look crossed

Many babies have a wide, flat bridge of the nose and folds of skin at the inner corners of the eyes that hide some of the white and make the eyes look crossed. This pseudostrabismus is harmless and disappears as the face grows. However, only an examination can tell true from apparent squint, so any concern should be checked.

What is amblyopia?

For vision to develop normally, each eye must send a clear, focused image to the brain during early childhood. If one eye sends a blurred or misaligned image, the brain starts to ignore it to avoid confusion or double vision, and the connections serving that eye do not develop fully. The eye itself may look perfectly healthy; the problem lies in how the brain processes its signals.

Main causes of amblyopia

• Strabismic amblyopia: the brain suppresses the image from the turned eye.
• Refractive (anisometropic) amblyopia: one eye has a much stronger prescription than the other, so it is always out of focus. This is common and easily missed, because the eyes look straight and the child sees well with the good eye.
• Bilateral refractive amblyopia: both eyes have a large uncorrected prescription, such as high long-sightedness or astigmatism.
• Deprivation amblyopia: something blocks the light, such as a congenital cataract or a very droopy eyelid. This is the most severe type and needs urgent treatment in infancy.

Early detection

Young children rarely complain about poor vision in one eye because they have never known anything different and their good eye compensates. That is why screening matters. Many countries offer vision screening around the ages of 4 to 5, and babies have eye checks shortly after birth and in the first weeks of life. Our guide to a child's first eye examination explains when to book.

Signs parents may notice

• An eye that turns in, out, up or down, all the time or only at times.
• Frequent squinting or closing one eye, especially in bright light.
• Tilting or turning the head to look at things.
• Clumsiness, bumping into objects or poor depth judgement.
• Objecting strongly when one eye is covered, but not the other.
• A white or unusual reflection in the pupil in photos, instead of the normal red reflex.

Note that it is normal for a newborn's eyes to wander occasionally in the first few months. A constant turn at any age, or any turn after about 4 months, should be checked.

Treating amblyopia

Treatment aims to give the brain a clear image from each eye and then encourage it to use the weaker eye. Large clinical trials by the Pediatric Eye Disease Investigator Group (PEDIG) have shaped modern practice.

Step 1: Glasses

If there is a refractive error, glasses come first. Wearing the correct prescription full-time for several months, called optical treatment or refractive adaptation, improves vision substantially in many children with refractive amblyopia, and some need nothing more. Getting a young child to wear glasses can be challenging; see our guide to glasses for children for practical tips.

Step 2: Patching

Covering the stronger eye with an adhesive patch forces the brain to use the weaker one. PEDIG studies showed that, for moderate amblyopia, around two hours of daily patching can be as effective as longer regimes, while more severe cases may need more hours. Your eye team will tailor the schedule. Patching works best when the child does engaging close-up activities, such as drawing, puzzles or reading, while wearing the patch.

Atropine penalisation

An alternative to patching is atropine eye drops placed in the stronger eye, usually on a schedule decided by the eye doctor. The drops temporarily blur near vision in that eye, encouraging use of the weaker eye. Trials found atropine to be similarly effective to patching for moderate amblyopia, and many families find it easier because there is nothing for the child to remove. Side effects can include light sensitivity and, rarely, skin flushing; dosing is always determined by the doctor.

Binocular digital therapies

Traditional treatments work by suppressing the stronger eye. Newer binocular approaches instead show each eye a different version of a game or video, giving the weaker eye more contrast or essential information so both eyes must cooperate. Some systems use special glasses, tablets or virtual-reality headsets. Several randomised trials have shown benefit, and at least one system has received regulatory clearance in the United States for children with amblyopia. Results so far suggest these therapies can be comparable to patching in some groups, but they are used alongside glasses and under the supervision of an eye care professional, not as do-it-yourself apps.

How long treatment takes

Most children need several months of treatment, with vision checked regularly. Once vision stops improving, treatment is gradually reduced, because amblyopia can recur after stopping, especially in the first year. Success is highest in children under about 7, but trials have shown meaningful improvement in many children up to their early teens, particularly if they have never been treated before.

Treating strabismus

Treatment depends on the type and cause of the turn:

• Glasses, sometimes with bifocals, can fully correct accommodative esotropia.
• Amblyopia treatment comes first if one eye has reduced vision.
• Prisms in glasses can help some small deviations and relieve double vision.
• Botulinum toxin injections into an eye muscle can weaken it temporarily and are used in selected cases.
• Orthoptic exercises may help some types of intermittent exotropia and convergence problems.

Strabismus surgery

When non-surgical options are not enough, surgery adjusts the position or tension of one or more eye muscles to change the eye's alignment. The eye is not removed from its socket; the surgeon works on the muscles through a small opening in the clear membrane covering the white of the eye. It is usually a day-case procedure under general anaesthetic for children. Recovery typically involves a few days of redness and discomfort. More than one operation is sometimes needed, and surgery straightens the eyes but does not cure amblyopia, so glasses and patching may still be required. Find out more in our eye surgery options guide.

Options for teenagers and adults

It is a myth that nothing can be done after childhood. Adults with long-standing strabismus can have surgery at any age to improve alignment, which often improves appearance, self-confidence, field of vision and sometimes depth perception. Studies show strabismus surgery in adults is successful in most patients and has real psychosocial benefits.

For adult amblyopia, the picture is more limited. Vision in a long-standing lazy eye usually cannot be fully restored, although research into binocular treatments and perceptual learning shows some improvement in some adults. Equally important is protecting the good eye: people with amblyopia should wear protective eyewear for sport and risky work, because the stronger eye is their main eye for life. See eye safety at work and in sports.

A new squint in an adult is a different situation. It may be caused by nerve palsies, thyroid eye disease, diabetes, high blood pressure, myasthenia gravis or, rarely, problems in the brain, and it usually causes double vision. It always needs prompt medical assessment.

When to see a doctor

Arrange an eye examination for your child if you notice an eye turning at any age after about 4 months, frequent squinting, head tilting, one eye being covered or closed, a family history of squint or lazy eye, or a failed school vision screening.