This chapter governs the eligibility, allowance computations, and related provisions for the disability retirement program. This chapter applies to all persons who become members of the plan under this part on and after October 16, 1992, all persons who become members of the plan on and after October 16, 1992, subsequent to a refund, and to all members as of October 15, 1992, who elect under this part, pursuant to Chapter 21.5 (commencing with Section 23700), to be covered by the disability retirement program set forth in this chapter.