Objective examination of refractive power of cornea and lens. Autorefractomy shows the overal refractive power of the eye, helps in calculating diopters and perscripting of eyeglasses. Keratometry shows the refractive power of cornea in diopters. It is the major part of the formula for calculating diopters of the intraocular lens in cataract surgery. Keratometry is also required for perscription of contact lenses.
More on the equipment used for autorefractomy and keratometry, please read here.