If you become eligible for disability benefits even though you were doing substantial gainful activity because you are blind and age 55 or older, you are entitled to a trial work period if—

(a) You later return to substantial gainful activity that requires skills or abilities comparable to those required in the work you regularly did before you became blind or became 55 years old, whichever is later; or

(b) Your last previous work ended because of an impairment and the current work requires a significant vocational adjustment.