though you didnt consult me but since practo has assigned this question to me hence please note. actually  when you see the things  without  glasses  they  look  blurred  hence a little bigger due to blurred  margins  but  when  you start  using  correct  glasses  the blurred  margins get rectified  as a result  you perceive the objects or fonts as if they  have  gone smaller but actually this is the  normal  condition .