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What is amblyopia or lazy eye?

Amblyopia, also known as lazy eye, is the failure of the visual capacity to develop properly in one or both eyes due to a lack of use during the visual learning phase. It’s a pathology that begins in infancy, and if not diagnosed and treated on time, it will persist during adulthood. It is the most common cause of a loss of vision among children and young people in developed countries, and affects 3-4% of school-aged children.

When we are born, our sense of sight has not yet developed. We are not born with the ability to see; instead, it develops and is acquired over the first years of life and the process culminates at the age of 8-9 years (although over the first 4 years is where there is most progression in learning).

In many cases, amblyopia does not have any symptoms, as the child does not know “what it is to see properly” and adapts to the eyesight they have. This mainly happens in cases where just one of the eyes is affected, as they can see well with the other eye, so there aren’t any warning signs. For this reason, it's very important that where children are concerned, teachers, parents, relatives and paediatricians, are aware of any sign that might make them question their child’s eyesight (they move in close to objects, they don't pay attention, they are “clumsy”). Very often the problem lies in the fact that they can't see properly.

For optimum visual learning, it’s essential that both eyes receive a clean image of what we see, and thus send information to the brain allowing us to gain visual acuity. If the child has a problem that makes the image the received by the brain poor, at this stage, the brain will “cancel” the development of that eye, it will settle for the little it sees and become “lazy”.

Causes of lazy eye. How does it come about?

  • Strabismus: this means that that one or both of the child’s eyes deviate. So that it doesn't see two images, the brain will cancel the vision of the deviated eye, which impedes the normal development of that eye.
  • Optical defects (astigmatism, long-sightedness or short-sightedness): if there is a refractive error, the image the brain receives will be blurry and it will settle for the image it see and the learning curve will stagnate.
  • Anisometropia: this is the difference in dioptres (or size) between one eye and the other. When one of the two eyes has a higher prescription than the other, this image will be blurrier, so the brain, because of the mechanism explained above, will choose the eye with a lower prescription, and better vision, meaning that the other one “doesn't have to work":
  • Natural cause: this is when there is an obstacle in the visual axis, for example, a congenital cataract, opacity of the cornea, a ptosis (droopy eyelid), retina diseases...any pathology that interferes with the correct projection of the image to the brain will cause amblyopia.



In the majority of cases, the child is asymptomatic and develops normally; it’s only in the most obvious cases that we will identify “odd habits” like tilting their head, constant blinking, a droopy eyelid, not paying attention, falling easily, etc. These signs should alert parents and teachers to see an ophthalmologist specialising in infant or paediatric vision. Regardless of the child or baby's age and no matter how small they are, the problem can be examined and assessed.

As we know that amblyopia can be treated and the normal visual acuity of a child can be restored if diagnosis and treatment are undertaken early on, it's vital that all children (with or without symptoms, with or without a family history...) go for a check-up with a paediatric ophthalmologist at the age of 2-3 to assess the ocular motility, eyelids, the back and front of their eyes, and see whether they have refractive defects. Subsequent check-ups will depend on the findings from the initial examination. We would advise that healthy children also undergo a yearly check-up until the age of 9, which is when their visual learning ends, in case during growth there has been a change from the previous check up and to be able to treat it.

You can recover from lazy eye if it is diagnosed and treated before the age of 8, the treatment is most likely to succeed during the first 4 years and the probability of success decreases as we approach the age of 9, at which stage the eye's capacity to rehabilitate is practically nil.

What we do not learn over the first years of our life, will not be recuperated in adulthood. Not acting in good time may condemn the child with poor vision in one or both eyes, so early diagnosis and starting treatment as soon as possible is vital.


Lazy eye treatment

To treat amblyopia, the first thing is to identify the cause and correct it. If there is a refractive defect, for example, correct it with glasses or contact lenses; if there is a visual obstacle, a cataract (can be operated on), a droopy eyelid that covers the pupil (an operation can correct the height) and once the cause has been identified we can treat the lazy eye. To do so, the method proven to be most effective until now and yielding best results is occlusion of the healthy eye with a patch. The time and schedule of the occlusion will vary depending on the grade of amblyopia, the cause and age of the child. There are alternatives to occlusion, which go under the term penalisation. It consists of blurring the vision of the healthy eye.  Penalisation can be optical (through correction that may not be appropriate for the healthy eye) or pharmacological (putting an eye drop in the healthy eye to blur the vision) and forcing the amblyopic eye “to work”. These methods are a second option we would only indicate them in the cases where complete correction with a patch fails.

In summary, to get good visual acuity as an adult, early diagnosis and treatment of amblyopia is fundamental.

It’s never too early for a child to have their eyes checked, while on some occasions it could end up being too late.

Professionals who treat this pathology

Frequently asked questions