steph28;
A day with dry eye shouldn't be cause for needing new glasses, but would add that a refraction ( eye exam ) may change from day to day. Possibly your surgery is causing the occassional dry eye, but, there are other causes.
Natural tears, or drops cause a bit of refraction themselves, so, that's why a dry eye equates to less than good vision. The tears, or drops are acting as a lens also. That is normal.
It's best just to tell the examining Opthamologist, or Optician you have occassional dry eye issues. Either, can check tear film strength and evaporation rate.
I have dry eye/poor Vs days and just blink a lot which causes the mebowmian gland above the eye to produce more tears because it is squeezed during a blink, or when eating.
You might ask the examiner about a punctum plug for the tear drainage hole.
Best wishes with this! ; )