There are a number of reasons why a child may be born with cataracts or develop them while they're still young.
But in many cases it's not possible to determine the exact cause.
Some of the main causes of childhood cataracts are described below.
Cataracts present from birth (congenital cataracts) are sometimes caused by a faulty gene being passed to a child from their parents.
This fault means that the lens does not develop properly.
It's estimated there's a family history of congenital cataracts in around 1 in every 5 cases of the condition.
Recent research suggests genetic causes are responsible for the majority of bilateral congenital cataracts in the UK.
Cataracts can also be associated with conditions caused by chromosome abnormalities, such as Down's syndrome.
Chromosomes are the parts of the body's cells that carry the genes.
Congenital cataracts can also be caused by infections caught by the mother during pregnancy.
The main infections linked to an increased risk of congenital cataracts include:
- rubella (german measles) – a viral infection that can cause a red-pink spotty skin rash
- toxoplasmosis – a parasitic infection caught by consuming food, water or soil contaminated with infected cat's faeces
- cytomegalovirus (CMV) – a common virus that can cause flu-like symptoms
- chickenpox – a mild but highly infectious condition caused by the varicella-zoster virus
- herpes simplex virus – a virus that often causes cold sores
Cataracts that develop in children after they're born are known as acquired, infantile or juvenile cataracts.
Causes of this type of cataracts can include:
- galactosaemia – where the sugar galactose (which mainly comes from lactose, the sugar in milk) cannot be broken down by the body
- diabetes – a lifelong condition that causes a person's blood sugar level to become too high
- eye trauma – as a result of an injury to the eye or eye surgery
- toxocariasis – a rare parasitic infection that can sometimes infect the eyes, spread from animals to humans via their infected faeces
But most of these problems are either rare or do not usually cause cataracts to develop in children.