Eye problems are going undiagnosed in many children because of poor screening services and a low uptake of free NHS tests, experts have warned.
Eye tests are free for under-16s on the NHS
A report from the Association of Optometrists says research suggests 5% of children aged six and 10% of 12 year olds have an uncorrected eye problem.
Screening services in England are patchy and many parents do not know under-16s can get free tests, it said.
The government said it was keen to ensure parents knew about free tests.
The AOP, which commissioned the report with the Association of British Dispensing Opticians and the Federation of Ophthalmic and Dispensing Opticians, called for a review of how many children have access to vision screening.
In the past eye checks were carried out at various points in a child's life, by a health visitor or at school.
It varied around the country but tests were commonly carried out at age five, seven and sometimes 11.
But in 2004, the government announced proposals for a national screening programme for four to five year olds.
The report found there was little data being collected on how many children were being screened, but anecdotally there seemed to be a "huge variation" in services in England.
Parents should be made more aware that children are eligible for free NHS sight tests on the high street, the report said.
Common problems in children, which need to be picked up as soon as possible, include lazy eyes, squints and long and short-sightedness.
Undetected problems can seriously damage a child's eye health, affect their child's social and academic development and lead to permanent visual problems in later life, experts warn.
The Association of Optometrists' chief executive, Bob Hughes, said it should be mandatory for children to have an eye test before starting school.
David Butler, chief executive of the National Confederation of Parent Teacher Associations, said: "The report provides evidence of the need for children to have their eyesight tested regularly and at an early enough stage for problems to be treated effectively."
Professor David Thomson, head of optometry and visual sciences at City University, said: "In an ideal world all children would be taken for regular eye examinations by an optometrist and a publicity campaign may help raise awareness.
"I believe that this should be backed up with high-quality vision screening in schools, ideally at the age of four to five, seven and 11."
The Department of Health said it did not collect information on how many pre-school children had been tested by optometrists.
A spokesman added: "Information about the extensive arrangements for providing help with NHS optical services and other health costs are publicised in leaflets and posters are also available for display in optical practices and hospital out-patient departments."