A retinoscope is an ophthalmic instrument used to examine and measure the refractive errors of the eye. Synonyms for retinoscope include ophthalmoscope which is an instrument used to examine the interior of the eye, phoropter, a medical instrument used to measure refractive errors in the eye, and refractometer, a device that measures the refractive index of a substance. Other synonyms for retinoscope are keratometer, a medical instrument used to measure the curvature of the cornea, and autorefractor, an automated instrument used to quickly measure the refractive error of the eye. These synonyms all refer to instruments or devices used in ophthalmology to determine the visual acuity of a patient.