Amblyopia, more commonly known as lazy eye is the condition affecting 4% of the general population, wherein one eye has less vision than the other.

It is usually detected at the time of school vision screening or following a routine visit to the optician. lazy eye is typically entirely asymptomatic although it may be associated with a squint in some cases.

Confusingly though, other conditions can be referred to as lazy eye as well. These include:

It is important to differentiate between these conditions and the information provided on this page is exclusively about amblyopia.

The causes of amblyopia include:

Difference in the power of the two eyes:

If the refractive power of each eye is significantly different, so if one eye has a high minus or plus power, the brain chooses to use the other eye to see. This results in under development of the eye with the high error.

Squint or Strabismus:

Some children may be born with or develop a squint, which leads to the eyes being misaligned. As a result, when one eye looks straight ahead the other may be turned in or outwards. If this is a constant phenomenon it leads to poor vision in the deviating eye.

Stimulus deprivation:

This occurs when the vision of one, or both, eyes is impaired temporarily by a cataract, or a droopy eyelid in childhood. This leads to an unequal signal to the brain from the two eyes and as a result the eye with the worse vision under develops, even when the deprivation is removed.

Treatment of amblyopia:

The principle behind amblyopia treatment, is penalising the good eye to allow the eye with the poorer vision to develop further. Treatment should be instituted as soon as possible after diagnosis and works best before the age of seven. The treatment methods include:

Patching of the good eye:

This can be carried out between 30 minutes to six hours a day, depending on the severity of the Amblyopia. Recent reports suggest that a maximum patching time of two hours is sufficient for most moderate cases.


In children unable, or unwilling, to patch, drops can be used to blur the vision on the good eye on a semi-permanent basis. This has the advantage of avoiding a potentially socially stigmatising patch and has been shown to be as good as patching in most cases.

Squint surgery:

For the best results, surgery in patients with amblyopia should be carried out once the treatment is complete and no further improvement in vision is expected.

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Mr Saurabh Jain

Saurabh Jain Is a Consultant Ophthalmic Surgeon and Clinical Director of services at the Royal Free London NHS Foundation Trust.