Tonometry and glaucoma

This is my first post and I am new to allnurses. Here's the scenario. I just finished preparing a statement for a course online discussion board for pharmacology class, and this week's forum discussed glaucoma medications. One of the questions my instructor asked was "how does the nurse know if the medications are effective?" In my response I said that pain scale was a factor, but since the goal of glaucoma meds are to lower IOP, I was thinking it is completely arbitrary for a nurse to use pain reduction to test effectiveness in this case. I was thinking that a scientific approach would be patient's report of pain reduction plus a tonometry test to measure effectiveness. So with that said, is use of a portable handheld tonometer as a tool to measure IOP within the nursing scope of practice? Or is tonometry only in the physician's scope of practice? Thank you.