n. - Measurement of the range of vision, esp. by means of the optometer.
n. - As defined (with minor variations) in the statutes of various States of the United States:
n. - "The employment of subjective and objective mechanical means to determine the accomodative and refractive states of the eye and the scope of its function in general."
n. - "The employment of any means, other than the use of drugs, for the measurement of the powers of vision and adaptation of lenses for the aid thereof."