A refraction test, also known as a vision test or eye exam, is a routine part of an eye examination that measures a persons prescription for eyeglasses or contact lenses. During the test, the eye doctor uses a phoropter, a lens comparison device, to place different lenses in front of the patients eyes while they read from an eye chart. The device allows the doctor to quickly switch between different lens types to determine the right prescription for the patient. The test is used to diagnose refractive errors, which occur when the light is not bending properly when it passes through the lens of the eye, causing blurry vision. The results of the test are used to determine whether a person needs glasses or contact lenses and what prescription lens they need to see properly. The vision level achieved during the refraction test is called the best-corrected visual acuity (BCVA) . The test can also help diagnose more serious eye conditions such as macular degeneration or retinal detachment. People with a refractive error should have an eye exam every 1 to 2 years, or when their vision changes. Regular eye examinations are crucial for maintaining the health of your vision and detecting various conditions and diseases that may affect your eye health and vision over time.