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Lazy eye (amblyopia): causes, treatment and why early testing matters

A lazy eye, which eye doctors call amblyopia, is weaker sight in one eye, or now and then in both, that develops in early childhood because the brain did not learn to use that eye properly. The eye itself often looks normal. It affects a few children in every hundred. Found in the early years, it usually responds well to treatment; found late, much less can be done. For all children's eye care at ReNew Vision, see children's eye care and squint treatment in Vasco.

What exactly is a lazy eye?

We see with the brain as much as with the eyes. From birth until about seven or eight years of age, the nerve pathways for vision are still being wired up by the pictures each eye sends to the brain. If one eye keeps sending a blurred or mismatched picture, the brain relies on the clearer eye and turns down the signal from the other. That eye then cannot see sharply even with the right spectacles, because the problem now sits partly in the brain's wiring. The word "lazy" is misleading: the eye muscles are not weak, and the child is not failing to try.

Is a lazy eye the same as a squint?

No, although the two are often mixed up, and many people say "lazy eye" when they mean an eye that turns. A squint (strabismus) is about the direction the eyes point: one eye turns in, out, up or down. A lazy eye is about how well an eye sees. A squint is one cause of a lazy eye and a child can have both, but many lazy eyes look perfectly straight. Straightening a squint, for example with surgery, does not by itself bring back sight in a lazy eye; the vision is treated separately, usually first. For eye turns and their treatment, see children's eyes and squint and squint surgery.

What causes a lazy eye?

Anything that stops one eye sending a clear, matching picture to the brain in early childhood can cause amblyopia. The main causes are:

• Unequal spectacle power between the two eyes (anisometropia). One eye may be much more long-sighted, short-sighted or astigmatic than the other. This is the cause most often missed, because the eyes look straight and the child gets along well using the better eye.
• A squint. To avoid seeing double, the brain switches off the picture from the turned eye, and with time that eye loses sharpness.
• High power in both eyes. When both eyes need strong spectacles and the child has none, neither eye sends a clear picture, and vision can stay below normal in both eyes even after spectacles are given (bilateral amblyopia).
• Something blocking the view (deprivation amblyopia). A cataract present at birth or in infancy, a drooping eyelid that covers the pupil, or a scar on the clear front window of the eye. A large eyelid lump such as a chalazion can also blur one eye by pressing on it. This type is less common but the most urgent, because in a baby it can cause deep amblyopia within weeks.

The risk is higher in children born early or small, and when parents or brothers and sisters had a squint, a lazy eye or strong spectacles.

Why does early testing matter so much?

• A child will not tell you. With one good eye, a child reads, plays and watches television normally. The weak eye is usually discovered only when each eye is tested on its own, with the other covered.
• The brain is most adaptable when young. In general, treatment started at three to five years improves vision more, and often in less time, than treatment started at nine or ten. That is not a hard cut-off, and older children can still gain, but every year counts.

A full children's eye check for lazy eye includes testing each eye separately with pictures, shapes or letters suited to the child's age, checking how the eyes line up and move together, measuring the spectacle power after drops that relax the eye's focusing, and examining the lens, retina and optic nerve. A school screening is a useful first filter, not a full check; if a child is referred from school, book the complete examination. The age-by-age warning signs are listed in signs your child needs an eye test or glasses.

How is a lazy eye treated?

Treatment first gives the weak eye a clear picture, then encourages the brain to use it. The eye doctor plans the steps for each child, depending on the cause, how weak the eye is and the child's age. In general terms:

• Removing the cause. Spectacles correct unequal or high power. A cataract or a drooping lid blocking a baby's vision has to be dealt with early, sometimes with an operation, and the eye doctor arranges this without delay.
• Spectacles alone, worn full time. Vision in a lazy eye often keeps improving for several months with spectacles only, so the eye doctor may watch and re-test before adding anything else. Tips on frames that suit young children are in spectacles for children.
• Patching. An adhesive patch covers the stronger eye for a set number of hours a day, so the brain has to use the lazy eye. Milder cases often need only a couple of hours daily, deeper ones longer. Lazy eye patching at ReNew Vision is planned and reviewed by the eye doctor.
• Blurring eye drops. For some children, a drop put in the stronger eye blurs its near vision for a time, which pushes the brain to use the lazy eye. Studies have found it works about as well as patching for moderate amblyopia. It is a prescription medicine, used only as the eye doctor directs, and it can make bright light uncomfortable. It does not suit every child; ask the eye doctor whether it is an option for yours.
• Newer methods using games or videos that show different images to each eye are being studied; they do not yet replace the methods above.

Regular reviews measure each eye, adjust the hours and make sure the stronger eye keeps its vision. When the lazy eye stops improving, treatment is usually reduced step by step rather than stopped all at once, because a lazy eye can slip back, and checks continue for some time afterwards. If a squint remains once vision has improved, squint surgery may then be considered.

How can parents help a child through patching?

• Make it routine. Patch at the same time each day, for example after school, and use a sticker chart for each completed day.
• Keep the eyes busy up close. Colouring, puzzles, threading beads, reading and hand-held games make the lazy eye work harder than watching from across the room.
• Look after the skin. In Goa's heat and monsoon humidity, patches get sweaty. Patch under a fan, dry the skin first, shift each new patch slightly, and tell the eye doctor if the skin gets sore.
• Keep going. Keep the spectacles on during patching unless told otherwise, and after a missed day simply carry on. Treatment usually lasts months, and stopping too soon is a common reason it works less well.

Can adults with a lazy eye be treated?

Most adults with a lazy eye have had it since childhood: it was never found, or treatment stopped early. After childhood the brain changes much less easily, so the vision in an adult's lazy eye usually improves far less than it would in a young child, and no treatment can promise a change. Even so, a visit is useful:

• Check the spectacle power. An up-to-date prescription can sharpen the lazy eye a little and make both eyes more comfortable.
• Do not blame every change on the old lazy eye. If sight in that eye seems to get worse in adult life, it may be something new, such as cataract, glaucoma or a retina problem, and it needs a full examination. Read more on the complete eye check-up.
• Protect the good eye. When one eye does most of the work, an injury to it affects daily life far more. Wear protective eyewear for cricket, grinding, welding, cutting and other risky work, and keep up regular eye check-ups.
• Know the vision rules. Driving licences and some jobs set vision standards for each eye; see eye fitness certificates.
• An eye that also turns can still be aligned with squint surgery in adults, though this does not improve the lazy eye's sight.

How do I book a lazy eye check at ReNew Vision?

Lazy eye testing and treatment, including patching and follow-up, is done at ReNew Vision Eye Hospital in Vasco. Children's eye care is a special interest of our eye doctor.

• Where: 2nd floor, Pai Hospital building, Vaddem Merces Road, Vaddem, Vasco da Gama, Goa 403802. See timings and directions.
• When: Eye OPD Monday to Saturday, 4 pm to 7 pm, after school hours. Sunday OPD closed.
• Call or WhatsApp: 072489 88039.
• Bring: present spectacles, earlier prescriptions and patching notes, and any school screening slip. The drops used to measure a child's power blur near vision for some hours.

Questions patients ask

Can a lazy eye get better on its own without treatment?

Usually not. Spectacles alone improve many lazy eyes, but an untreated lazy eye tends to stay weak for life once the brain's vision pathways have matured. That is why a lazy eye found in a young child should be treated rather than watched.

How many hours a day should my child wear an eye patch?

It depends on how weak the lazy eye is and on the child's age. Milder cases often need a couple of hours a day, deeper ones longer. The eye doctor sets the hours and changes them at each review, so do not change them on your own.

Is it too late to treat a lazy eye at 10 years or in the teenage years?

Not always. Treatment works better the younger the child, but older children and some teenagers, especially those never treated before, can still gain useful vision. A full check shows whether treatment is worth trying.

Can a lazy eye be treated in adults?

Improvement in adults is usually small, because the brain changes much less after childhood, and no result can be promised. Adults still benefit from an up-to-date spectacle power, a check for any new eye disease, and protecting the stronger eye.

Can surgery fix a lazy eye?

Surgery can straighten a squint or clear something blocking the view, such as a cataract in a baby, but it does not by itself restore sight in a lazy eye. The vision is improved with spectacles, patching or drops.

Can a lazy eye come back after patching stops?

Yes, in some children the vision slips back. That is why the eye doctor reduces patching gradually rather than stopping it suddenly, and keeps checking the eyes for some months after treatment ends.

This page is general eye-health information, not personal medical advice. Your eye doctor advises you after examining your eyes.