Causes of Lazy Eye (Amblyopia)


Lazy eye is caused by an eye not being used properly in childhood.  In rare instances both eyes may be affected but it is predominately a condition that only affects one eye. 

We are born with some vision.  During early childhood the visual pathways continue to develop within the eye and the brain up until around the age of 8 years.  After this the visual pathways stop growing and developing and will remain as they are for the rest of our life.  Due to a number of reasons, if you cannot use your eyes normally, then vision is not learnt properly.  This causes vision to be impaired and is called amblyopia.  Thus, the condition is a developmental problem of the brain instead of a problem within the eye.  The reasons for not using both eyes properly include the following:

Squint

Also referred to as strabismus.  This is a condition when eyes look in different directions.  One eye may be looking straight ahead and the other may point inwards, outwards, up or down.  This means that eyes may focus on different objects.  In order to avoid seeing double, the brain automatically ignores one of the eyes and just relies on the eye that is looking straight ahead.  Not all instances of squint eye result in only one eye being used.  If the eye that is used to focus switches from time to time, both visual pathways develop as normal but one eye may remain dominant.  When the brain completely ignores the signals from a non-dominant eye, its normal visual pathways don’t develop properly and amblyopia develops.

Refractive Errors

Short sight (myopia), long sight (hyperopia) and astigmatism are all refractive errors, which may cause lazy eye.  These refractive errors are due to problems with focusing of light through the eye lens.  If there is a difference in refraction in the two eyes, anisometropia may result.  This is because the brain will ignore signals from for example a myopic eye and due to this, amblyopia may result.

Cataract/Other Conditions

Any eye disorder which prevents good vision can cause amblyopia such as cataract.  This is because the brain does not learn the visual pathways properly.  It is therefore essential that any childhood eye condition such as a cataract or a scarred cornea must be treated early.

Injury

Eye trauma can cause amblyopia at any age.

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