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What is lazy eye?

What is lazy eye?

darrenBy Dr Darren Stoler

Many people, when asked what they think the term “lazy eye” means, respond by saying “one eye that is squint”. The truth is a lot more complicated, and important for parents of young children to be aware of: Not all squints are lazy eyes, and not all lazy eyes are squints, and lazy eyes can be prevented or even cured, if the problem is caught early on in the development of your baby’s brain.


In fact, the term ‘lazy eye’ is not accurate – a more accurate term would be ‘lazy brain’. In my previous article for SA Moms, I wrote about the important milestones your baby should reach at certain key points in their development. The very reason that these milestones exist at all, is that the brain is growing, developing, forming new connections constantly. The eye and the brain have to learn to ‘speak the same language’ over time, as these new connections between the eyes and the brain form.

The medical term for a lazy eye, is ‘amblyopia’. Amblyopia occurs when the eye and the brain never learn to speak the same language and form those connections. The developing brain is an amazing organ, and can form these new connections with the rest of the body easily – in the first two years of life, most connections are formed. New connections can still be formed until 7 years old, after which the brain cannot form new connections any more. Amblyopia occurs when a child doesn’t use their one eye properly, or uses one eye more than the other, and the connections between the unused eye and the brain don’t form.

There are many reasons why one eye may not be used as much as the other eye. The most common cause of this is a squint in one eye – medically we call this a ‘strabismus’. If a child has a squint with one eye that doesn’t look where the other eye is looking, the brain starts to see double vision, and doesn’t like it, so to avoid the confusion of double vision, the brain literally turns off the signal from the squint eye in a process called ‘suppression’. If this occurs for a long period of time, especially before two years of age, but even until seven years old, then amblyopia will develop – the eye and the brain won’t form the communication pathways necessary to send good signals to each other. And even if the squint is repaired after the age of seven, the amblyopia is usually permanent – the brain is no longer able to form those new connections after seven years old. The result is then a totally normal eye, and a totally normal brain – but the eye can’t see!

Amblyopia doesn’t only occur with squints. Any condition which causes blurring of the vision in one or both eyes can lead to amblyopia – if a child is very short-sighted, or has high astigmatism in one or both eyes, the vision in that eye will be blurred, and the brain will ignore/supress the signal from that eye. If a child has a cataract or other anatomical abnormality that is not corrected early, the brain will do the same thing – ignore the poor signal from the damaged eye, instead choosing to focus on the eye sending a clear picture. If the glasses error is not corrected at a young age, or the damaged eye not repaired in time, amblyopia will be the result – a permanent inability for that eye to see – even if glasses are given after the age of seven.

That is why it is so important to find a non-seeing eye in a young child. If we catch these problems early (and the earlier you catch them, the better), we can fix the underlying cause of one eye not seeing, and this helps the eye and the brain to make those connections before its too late. Sometimes, the treatment is as simple as patching the ‘good’ or healthy eye closed for a few hours each day, in order to force the child to use the weaker non-seeing eye. This forces the eye and the brain to work together, and make those essential new connection pathways.

Amblyopia is common – in the USA and the UK studies show around 2-3% of all children are affected by amblyopia. This makes it the most common cause of blindness in one eye (monocular blindness) in the USA. This is why good preschool programs do routine screening for poor vision and glasses errors in young children between 3 and 5 years old. Parents should be aware that a small squint in a young baby or child is not a benign condition, and the old adage of ‘leave the squint until the child is older’ is definitely not the correct approach in managing children with squints!

If you have any questions or comments, feel free to email me: dstoler@morningside-eye.co.za