(a) Once each year during the first five years after a person retires for disability, and once in each three-year period after that, the board of trustees may require a disability retiree who is less than 60 years old to undergo a medical examination by one or more physicians designated by the board.
(b) If a disability retiree refuses to submit to a medical examination as provided by this section, the board of trustees shall suspend the retiree's annuity payments until the retiree submits to an examination. If a retiree has not submitted to an examination as provided by this section before the first anniversary of the date of first refusal, the board shall revoke all rights of the retiree to an annuity.