Lazy eye (amblyopia)

A lazy eye, or amblyopia, is when one eye sees less well than the other not because of any disease of the eye itself, but because in the earliest years of life the brain never learnt to use it. In most cases the eye is perfectly well formed. That is why amblyopia nearly always runs silently: the child does not complain, sees well with the other eye and behaves entirely normally, and the difference only comes to light at a sight test. And that is precisely why finding it in time matters so much: while the visual system is still forming, the situation can be put right; later on it cannot.

Why the brain stops using an eye

Sight does not arrive ready-made at birth; it is built during the first years. For the parts of the brain that handle vision to develop, they need a steady flow of sharp pictures from both eyes. If one eye sends a blurred image, or a displaced one, or none at all, the brain faces a problem with no solution: the two pictures do not match. Its way out is a simple one — it suppresses the signal from the weaker eye and works with the better one alone.

From there a vicious circle sets in. The less the brain uses that eye, the poorer its connections with the visual cortex become, and the further its vision falls behind. After a few years an anatomically healthy eye sees badly, and glasses no longer put it right: the letters land sharply on the retina, but there is nobody to process them.

Hence the guiding rule: treatment is not about curing the eye but about making the brain use it again. And that only works while the visual system still has plasticity — that is, in childhood.

Why it happens

There are essentially three causes, and they are treated differently.

• A squint. The eyes point in different directions, the pictures do not match, and to escape double vision the brain switches one of them off. Here the deviation can be seen from outside, and parents usually notice it themselves.
• Different optics in the two eyes. One eye is, say, strongly long-sighted or markedly astigmatic while the other sees normally. The brain takes the sharp image and suppresses the blurred one. This is the most treacherous cause: there is nothing whatever to see from outside — the eyes are straight, the child complains of nothing, because the good eye sees well and no other kind of vision is known. Amblyopia like this is found only by testing sight. If a high degree of long sight or astigmatism is the same in both eyes, both can fall behind.
• Something blocking the path of light. A congenital cataract, a drooping eyelid covering the pupil, a clouded cornea. The image simply never reaches the retina, and this form of amblyopia develops fastest and runs deepest. Here help is needed not "at some point" but in the first weeks of life.

It is worth knowing separately what raises the likelihood of amblyopia: prematurity, low birth weight, a squint or severe sight problems in close relatives, and also certain syndromes and developmental delay. In those cases the child is seen by an eye specialist earlier and more often, without waiting for a routine check.

How to spot it

The most important point bears repeating: most children with amblyopia show no signs at all. Everything below is worth checking, but its absence proves nothing.

• the child covers or screws up one eye, especially in bright light;
• tilts or turns the head when looking at something;
• one eye drifts, either constantly or only when the child is tired, unwell or lost in thought;
• holds books and toys close to the face, moves right up to the screen;
• judges distance poorly: misses when catching a ball, trips on steps, catches corners;
• rubs the eyes, complains of tiredness and headache after reading or drawing;
• does not follow objects with the eyes or hold a gaze on a face.

There is a simple thing you can do at home: cover first one eye and then the other with your hand while the child is absorbed in something interesting. If covering one eye brings protest while the other is accepted calmly, there is a difference, and that is reason to see a specialist. The test is crude and no substitute for an examination, but it is better than nothing.

Older children sometimes say themselves that one eye sees worse, or cannot make out the board while reading a book without difficulty.

What cannot wait

Some signs call for an eye specialist urgently rather than at the next convenient moment:

• a white or yellowish glint in the pupil — in dim light, when looked at from an angle, or in flash photographs where the other eye gives the usual red reflection and this one shines white. That can be how a congenital cataract shows itself and, more importantly, a retinoblastoma, a tumour of the retina in young children that can be beaten when treated early;
• a squint appearing suddenly in a child over three or four months, particularly alongside double vision, headache or vomiting;
• a striking recent difference in the size of the pupils or the colour of the irises;
• an eyelid completely covering the pupil in a baby;
• sudden loss of vision in one eye over hours or days, pain in the eye, redness with failing sight;
• any new squint or double vision in an adult — a separate situation altogether, calling not for a new spectacle prescription but for investigation.

In babies under three or four months the eyes sometimes wander and drift apart briefly; that is acceptable. A sustained deviation at any age, and any deviation after four months, is not.

What a sight test involves

Sight can be tested at any age, including infancy: the child does not need to know letters or to talk. There are picture charts, cards with stripes, and instruments that assess the optics of the eye in seconds.

The examination usually covers visual acuity in each eye separately, the position of the eyes and their movement, an assessment of the optics and a look at the back of the eye. For accuracy, drops are put in that widen the pupil and briefly relax the focusing muscle: without them a child's eye adjusts itself and hides its true long-sightedness. After the drops the pupils stay wide for several hours, sometimes up to a day, near vision is poorer and light feels harsh — best not to plan reading or homework for that day, and to take sunglasses out with you.

The timing of routine checks differs from country to country, so follow your national programme and your doctor's advice. The general principle is this: the eyes are first examined in the maternity unit, vision is then assessed at routine appointments with the paediatrician, and a full sight test is carried out in the pre-school years, before the window in which treatment works has closed. If a child is in a higher-risk group or something has caught your attention, there is no need to wait for the scheduled date.

Treatment, and why timing matters

Treatment almost always begins not with a patch but with glasses. For many children properly prescribed glasses worn all day restore vision on their own, simply because the brain finally starts receiving a sharp picture. That takes several months, and there is no need to rush into anything more active meanwhile.

If glasses are not enough, the better eye is limited for a time so that the weaker one has to work. This is done in two ways:

• occlusion — patching. An adhesive patch goes over the healthy eye for some hours a day; exactly how many is for the doctor to decide, and "the more the better" does not apply here;
• drops that temporarily blur the vision of the better eye. The results are comparable to patching, and they are a rescue when a child flatly refuses a patch or the skin under it becomes irritated.

Where the cause is something blocking the light, it is removed surgically: a congenital cataract is operated on in the first months of life, and delay there costs sight. Squint surgery straightens the eyes but does not itself treat the amblyopia: patching or drops carry on regardless, before the operation or after it.

About timing it is worth being blunt. Treatment works best in the pre-school years, and by around seven the scope narrows sharply because the visual system loses its plasticity. That does not mean treatment after seven is pointless: improvement is possible in older children and teenagers, it simply comes more slowly and is rarely complete. A diagnosis made at eight is a reason to start now, not to give up.

Doing nothing has a further side that is easy to overlook. Someone with untreated amblyopia effectively lives on one eye: full depth perception is missing, and if anything happens to the good eye — an injury, a detachment, glaucoma — there is nothing to fall back on. That alone justifies a few months of patching in childhood.

Seeing the treatment through

The hardest part of amblyopia is not medical. A child is asked to cover the eye that sees well and use the one that sees badly. Resistance is only natural, and whether it can be overcome does more for the result than the choice of method.

• Fill patching time with close-up activities the child enjoys: drawing, building sets, board games, reading aloud together. Sitting passively in front of a screen works less well.
• Use a timer and a sticker chart, so that the child can see progress and you can see the real number of hours rather than an impression.
• Tell the nursery or the school: during this period the child finds the board harder to see and may look inattentive.
• Keep an eye on the glasses. If they slip and the child looks over the top of the frames, there is effectively no treatment going on. Frames are chosen to fit the face and adjusted at the optician's as the child grows.
• If the skin becomes irritated, try a patch from another maker or a matt cover over the spectacle lens.
• Do not stop treatment on your own as soon as the two eyes level up: it is withdrawn gradually, or what has been gained is often lost. Follow-up continues until the doctor is satisfied that the result is holding.

One more thing: avoid talking about the "bad eye" in front of the child. Children take it literally and start to feel self-conscious. It is easier to say that this eye is in training and the patch is its gym.

Online consultation

At an online appointment the doctor goes through what you have noticed in your child — screwing up the eyes, a tilted head, an eye that drifts — and judges what falls within the normal range for that age and what needs examining in person, and how urgently. The warning signs that mean seeing an eye specialist without waiting for a slot are covered separately, including a white glint in the pupil in photographs. If the diagnosis has already been made, the doctor helps you make sense of the regime you have been given: how many hours of patching, what to occupy the child with during them, what to do about skin irritation and outright refusal, and why treatment is not abandoned at the first signs of success. An adult with long-standing amblyopia is told what can realistically be done now and how to protect the good eye.

This material is for information only and does not replace medical advice.