The Collaborative International Dictionary of English v.0.48:

Optometry \Op*tom"e*try\, n.
   1. (Med.) Measurement of the range of vision, esp. by means
      of the optometer.
      [Webster 1913 Suppl.]

   2. As defined (with minor variations) in the statutes of
      various States of the United States:
      (a) "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."
      (b) "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."
          [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

optometry
    n 1: the practice of an optometrist