Doctors use an eye screening chart to diagnose whether their patients need glasses or not. Usually, the patient needs to stand sixteen to twenty feet away from the eye chart in order for the doctor to properly perform the test. An eye chart usually contains letters, with the biggest letters on top, and gradually the letters get smaller and smaller. The smaller the letters a patient can read, the better his or her vision. Some charts contain pictures and symbols in stead of letters. These charts are for small children, foreigners, or illiterate people who cannot read American letters. Perfect vision is 20/20 vision. This chart is for doctors to diagnose whether their patients need eyeglasses or not. This is not a formal eye test. If the pediatrician thinks that his or her patient needs glasses, he will send the patient to a optometrist, or an eye doctor.