Toby Smith had a rare eye condition

Up to two million children may be falling behind at school because of sight problems, the Royal National Institute of the Blind says.

Research involving 3,000 school-age children showed that between 17% and 22% had an undiscovered eye problem.

Parents are being urged by the RNIB to take their children for eye tests, which are free for under-16s and for anyone up to the age of 19 who is in full-time education.

The RNIB's figures have been released at the start of its Children's Eye Health Week.

Anita Lightstone, head of eye health at the RNIB, said: "Children rarely tell their parents that they can't see as they don't realise they have a sight problem.

Left undetected

"But a free eye test at your local optician can help diagnose a problem."

Many parents wrongly believe schools organise eye tests for children, the charity says.

It urged the government to introduce universal screening for children at ages five, seven and 11.

Ms Lightstone said some common conditions, such as short and long sight, and eye muscle co-ordination problems, could sometimes be cleared up without children having to wear glasses.

The spokeswoman added that in a few cases eye tests could also highlight more serious problems, such as cancer, that could cause blindness if left undetected.

Children rarely tell their parents that they can't see as they don't realise they have a sight problem RNIB spokeswoman 'My son almost went blind'

One case being highlighted by the RNIB is that of seven-year-old Toby Smith, from Norfolk, who came within just one month of going blind before a rare eye condition was diagnosed.

The RNIB urged parents to look out for the following tell-tale signs of poor vision:

• Their child seems distracted and finds it difficult to make friends

• They blink more than usual and get irritated when doing close-up work

• They sit very close to the television and hold objects close to their eyes

• They get headaches after using computers or reading

• They complain of itchy and irritable eyes.