Visual accuity is basically "sharpness of vision" it is based on the Snellen charts Ya know the chart, either the E's pointing in different directions, each line getting smaller or it is letters E F P T O Z .... Each line getting smaller. This does not say "why" you can't see clearly, The next steps determine why, nearsightedness, farsightedness, or astigmatism are the usually culprits. 20/20 is the average, normal "near enough to perfect" to where a person is considered to not be visually impaired. Less than that and they are considered out of the average 'normal' this doesn't mean that they need glasses, it may simply mean that they fall outside of that range we can loosely call "perfect" vision. 20/20 US (UK 6/6) is based on how we measure distance. 20 feet for the USA, 6 meters for the UK. In technical jargon we get into what basically boils down to being able too see a letter X size clearly from 20 feet (6 meters if you are in the UK) 20 20 is NOT perfect vision. It is the accepted "norm" the reality is that 20/15 is better vision, A person with 20/15 acuity can stand 20 feet away from an object and see it as well as a person with 20/20 acuity moving up to 15 feet away from the object to view it. 20/30 is poorer vision, meaning that what a person with 20/20 can see from 30 feet clearly is how the person with 20/30 vision. In other terms, the bigger letter are clearer to see. Mild visual differences are the norm. And since children are growing things their eyes balls are not perfect spheroids all the time and their vision can improve or get worse as they grow. Depending on WHY your son does not have 20 20 acuity (does he have 20/21or 20/19?) and how bad that is will determine if he needs corrective lenses.

Do you know what 20/20 means? It means that if it's 20 feet away it looks like it's 20 feet away. 20/50 means that if it's 20 feet away it looks like its 50 feet away. 20/10 means if it's 20 feet away it looks like it's 10 feet away. If your childs vision is less or more then 20/20 chances are he needs glasses. The longer you wait, the worse his vision will get. But get the advice of a professional.

It means his vision is less than perfect. Ask your pediatrician or optometrist if he needs glasses, because he may not -- my vision's about 20/30 or 20/40, and I can still see well enough to drive and stuff. Does your child have trouble reading the blackboard in class, or signs you see as you're driving down the street? These are the sorts of questions you should be asking.