(1) The medical status of each member receiving a disability benefit will be reviewed annually by the board to determine whether the member continues to be disabled, unless:
(a) the board determines reviews are unnecessary and may be discontinued;
(b) the board determines more frequent reviews are warranted by the nature of the disability;
(c) the board converts the disability retirement benefit of a participant in the defined benefit retirement plan to a service retirement benefit; or
(d) a participant in the defined contribution retirement plan receiving a disability benefit reaches 65 years of age.