"Permanent disability" or "permanently disabled" means physical incapacity to perform the duties of a law enforcement officer, fireman, or prison guard as determined by the public employer designated in paragraph (3) of Code Section 20345320-3-453, provided that such [...]

(3) "Permanent disability" means any disability which is permanent in nature or which is expected to continue for a period of at least five years.

(4) "Permanent disability" means disability due to: