A refraction test is usually given as part of a routine eye examination. It may also be called a vision test. This test tells your eye doctor exactly what prescription you need in your glasses or contact lenses.Normally, a value of 20/20 is considered to be optimum, or perfect vision.our doctor may also do this test without the help of a machine. In this case, he or she shines a light into each of your eyes and looks at the amount of light that is bouncing off your retina to measure your refractive score. Afterwards, your doctor will need to determine exactly what prescription you need.