One Year One Eyeglass

My hubby changes his eyeglass once a year. I do not understand why he wants to change eyeglass so often actually. I thought change it two or three once is consider ok already. Nevertheless, why he wants it every year? He never throws away his old eyeglasses actually. He has more than 10 pair’s eyeglasses at home now. I am just curious why he could not wear the old eyeglass since his eyes power never increase.