Section 4. Notwithstanding any provision of any contract or agreement entered into by the trustee or plan administrator of any fund authorized under this chapter, whenever such contract or agreement provides for reimbursement for any visual services which are within the lawful scope of the practice of a duly registered optometrist, reimbursement thereunder shall be made to either the registered optometrist or the registered physician of the insured’s selection. Visual services, as such term appears in the preceding sentence shall mean the optometric services provided by registered optometrists and physicians as set forth in chapter one hundred and twelve.