Notwithstanding Section 31720, any member covered under Section 31751 who is permanently incapacitated shall be retired for disability regardless of age if, and only if:
(a) The member’s incapacity is substantially caused by injury or disease arising out of and in the course of the member’s employment, or
(b) The member has completed a total of 10 years of service.
“Permanently incapacitated,” for the purpose of this section, means that the member is unable permanently to engage in any substantial gainful employment.