Sphere is used to indicate how myopic or hyperopic a person is. If a person is myopic, he or she will get a negative sphere number. If he or is farsighted a postive sphere number will result. If the person has a sphere number of zero, it is called a plano which means that a person doesn't have any problems with refraction. For a brief overview of lens or glasses prescription go to this site: http://www.usaeyes.org/lasik/faq/read-eyeglasses-contacts-prescription.htm.