The prescription glasses or prescription lenses are defined as lenses that are tailormade for you as per the eye number test performed by your eye doctor. This is first and most important step in getting the correct pair of glasses. Your eye doctor will perform both manual eye refraction test as well as computerized eye number test to ensure correct prescription number. Any errors in the refraction eye test or incorrect number results in the auto-refractometer test can cause wrong pair of glasses and complete waste of money. And therefore, it is important to get your eye number test done by a qualified eye doctor ( Ophthalmologist ).