All children in Reception year in state maintained schools in Harrow are offered vision screening. This is mainly to pick up amblyopia, which is also commonly called 'lazy eye'.
A lazy eye affects about 1 in 50 children and can be treated effectively if it is caught before the age of six. A lazy eye does not usually cause any symptoms. Younger children are often unaware that there is anything wrong with their vision. If a young child is aware that there is something wrong, they are usually unable to explain it. Left untreated, a lazy eye can lead to the eye's central vision never reaching normal levels. You can find more information about amblyopia / lazy eye here.
There are a number of other eye conditions that your child should be checked for. NHS eye tests are available for free at opticians for children under the age of 16 (under the age of 19 if they are in full-time education).
It is recommended that most people, including children, should get their eyes tested every 2 years unless your doctor, ophthalmic practitioner or optometrist thinks you should be tested more often. There is more information about eye testing for children here.
Search online to find your nearest optician.