Once each year during the first five years following the retirement of a member on a disability retirement allowance and once in every three-year period thereafter the Board may, and upon his application, require any disability beneficiary who has not yet attained the age of sixty-five years to undergo a medical examination to be made at the place of residence of the beneficiary or other place mutually agreed upon by a physician designated by the Board. Should any disability beneficiary who has not yet attained the age of sixty-five years refuse to submit to at least one medical examination in any such year by a physician designated by the Board his disability retirement allowance may be discontinued until his withdrawal of refusal and should his refusal continue for one year all his rights in and to his disability retirement allowance may be revoked by the Board.