Every optometrist licensed to practice in this state under title 63, chapter 8, has the right to become a participating optometrist in the vision service plan corporation operating in the county in which the optometrist resides or practices. A vision service plan corporation shall impose no restrictions on the optometrists who treat its subscribers as to methods of diagnosis or treatment. The private optometrist-patient relationship shall be maintained, and a subscriber shall at all times have free choice of any optometrist who is a participating optometrist in the corporation and who agrees to accept a particular beneficiary as a patient.