Eye doctor will determine the type and degree of refractive error by performing a test called a refraction. This can be be done with a computerized instrument (automated refraction) or with a mechanical instrument called a phoropter.
Refraction may reveal that one has more than one type of refractive error. For example, blurred vision may be due to both nearsighted and astigmatism. Eyeglass lenses and contact lenses are fabricated with precise curves to refract light to the degree necessary to compensate for refractive errors and bring light to a sharp focus on the retina.
Blurred vision is the most common symptom of refractive errors. Other symptoms may include: Double vision, haziness, glare or halos around bright lights, squinting, headaches, eye strain
Vision correction surgeries such as LASIK aim to correct refractive errors by changing the shape of the cornea, so that light rays are bent into a more accurate point of focus.