hello, i have a question.. is it possible for my powers to decrease.. how come?tq..

sorry.. i asked bcoz i'd like to buy new set of contact lens.. but i just checked my eyes the other day for new specs and they say my powers have decreased. before this i bought contact lens with powers -3.50® abd -3.25(L).. my new specs have powers -3.25® and -3.50 (L)... before buying new contact lens i'd like to make sure.. so the question was is it possible for my eyes power to decrease? tq.