(a) At least once each year during the first five years following the allowance of a disability annuity to any member, and at least once in every three-year period thereafter, until a member's attainment of age 55, the Board shall require any disability beneficiary to undergo a medical examination to be made at the place of residence of said beneficiary, or any other place mutually agreed upon, by a physician or physicians engaged by the System. If an examination indicates that the beneficiary is no longer physically or mentally incapacitated for service in the position held by the member at the date of disability, payments by the system shall be discontinued. The name of such member shall then he placed on the appropriate list of candidates maintained for appointment to a position in the division for which he is found to be qualified at compensation at least equal to the rate he received at the time he last became a beneficiary.
(b) Should any member receiving a duty disability annuity or nonduty disability annuity resume a gainful occupation, and his earnings therefrom together with his disability annuity exceed the rate of compensation of the member at the date of retirement, the System shall reduce the amount of disability annuity to an amount which, when added to the compensation being earned by the member, shall not exceed the rate of compensation of the member at the date he last became a disability beneficiary.
(c) Should any disability beneficiary refuse to submit to a medical examination as herein provided, payments by the system shall be discontinued until his withdrawal of such refusal, and should his refusal continue for one year, all rights of the member in any disability annuity shall be revoked by the System.