Is cup size change from .6 mm to .8 mm in a year rapid deterioration?

Question; if the cup of my optic nerve has expanded from .6 mm to .8 mm in a year, is this rapid deterioration, or slight deterioration?   Intuitively it seems like alot of deterioration, but I don't really know how much meaning it has.   However, a year ago it was considered on the borderline of normal at .6 mm.   After doing a nerve scan the glaucoma specialist thought at the time that it looked most like normal variation.  

Yours,

Dora Smith