Nothing in this chapter shall be construed as conferring on the holder of any certificate of licensure issued by said board the title of oculist, ophthalmologist, or any other word or abbreviation indicating that he is engaged in the practice of medicine or surgery, or the treatment or the diagnosis of diseases of, or injuries to, the human eye, or the right to use drugs or medicines in any forms for the treatment or examination of the human eye. However, optometrists who have been certified by the board under the provisions of Sections 73-19-101 through 73-19-109 may use diagnostic pharmaceutical agents in the practice of optometry in accordance with the requirements of Sections 73-19-101 through 73-19-109, and optometrists who have been certified by the board under the provisions of Sections 73-19-153 through 73-19-165 may use therapeutic pharmaceutical agents in the practice of optometry in accordance with the requirements of Sections 73-19-153 through 73-19-165. Nothing contained in Chapter 303, Laws of 1991, shall be construed as expanding the scope of practice of a licensed optometrist beyond that authorized prior to July 1, 1991.