Optometrist told me eye pressure has consistently been 20. one week later at glaucoma doctor office is 28. why difference?

Different devices: Different pressure measuring devices can give different pressure readings, so trust the ophthalmologist glaucoma specialist.

VariableEyePressure: Simply stated, the eye pressure (iop) can vary day-to-day, hour-to-hour. A 40% (20-28) increase from one day to the next seems unusual. Were the reading done on the same machine both times?... A baseline is most often established after 'several' readings, on machines that are identical (of have been regularly calibrated). Get this right before using your numbers.