Official health service guidelines which delay eye tests on children until they first start school could be exposing some of them to unnecessary bullying.

Researchers have discovered that children who have to wear an eye patch to treat the condition known as lazy eye are more likely to be bullied by other children as they go through school.

But if the test is conducted at a younger age - and if the patching treatment is completed by the time they start school - the children are less likely to be victims of the bullies.

The results come from an examination of 4,400 children who part of the Children of the 90s study based at the University of Bristol.

Bristol eye surgeon Cathy Williams set out to investigate the implications of the age of screening and treatment, for children who had suffered the condition amblyopia, (also known as lazy eye). Although it affects three per cent of children, it is simply treated with an eye patch, worn over the stronger eye.

Controversially, pre-school screening for amblyopia at the age of three has been abandoned in much of the UK on the grounds that all children can be checked more effectively at school age. It is said that the age at starting treatment is irrelevant. Under current guidelines, children should be tested by the school nurse, at the age of four or five.

Dr Williams said: "One argument for preschool screening is that patching treatment is more likely to have concluded before school starts, so avoiding adverse reactions from other children.

"We decided to test this by comparing two groups of children: those who had been offered preschool screening at the age of three and the others that hadn't."

At the age of eight, all the children were asked whether they had been bullied - physically or emotionally.

Dr Williams said: "In the group who had been offered preschool screening, there was an almost 50 per cent reduction in the proportion of children (who had been treated for amblyopia) who reported having been bullied.

"Whilst the causes of bullying are complex and linked to many factors, these data do suggest that the timing of intervention to detect amblyopia may lessen the likelihood of a child who is treated with patching being bullied.

"Both parents and children might consider that halving the risk of being bullied is a good reason for a child to attend a preschool vision screening appointment, rather than wait for detection and treatment at school age... especially since we know that repeated bullying is consistently associated with physical and emotional problems for the victims and may have long-term consequences.

“Reducing the need for patching treatment in school could be one way to avoid it.”