Section 6. A subscription certificate shall be issued to each subscriber of an optometric service corporation. Any agreement between an optometric service corporation and a group of ten or more persons or with the employer, employers or other representatives of such group whereby the optometric service corporation undertakes to furnish benefits for optometric service to said persons and their covered dependents, if any, shall be considered a group optometric service agreement. Under a group or non-group optometric service agreement, the form of the subscription certificate, the extent of optometric services contained therein, and the premiums charged by such corporation to the subscriber shall be filed with and receive the prior approval of the commissioner. No such agreement shall be approved if he finds that the extent of optometric services offered therein are unreasonable in relation to (a) the premium charged for such services, and (b) to the economic practicality of providing for such prepaid services, or if the premium charges are excessive, inadequate or unfairly discriminatory. No subscription certificate shall be issued unless the commissioner shall have approved in writing the form of certificate nor unless it contains in substance the following provisions:—

(a) A statement of the optometric service to be paid for by the corporation, and if any optometric service is excepted, a statement of such exception.

(b) A statement of the duration of the agreement and of the terms and conditions upon which it may be extended, renewed, revised, canceled or otherwise terminated.

(c) A statement of the period of grace which will be allowed for making any payment due from the subscriber under the contract, which in any event shall not be less than ten days.