Tonometry tests for glaucoma by measuring IOP (intraocular pressure), which is not to be mistaken for FFP or OPP. One can test for IOP grossly by pressing on the eyeball with the eyelid closed. If the eye bursts, you pushed too hard.
Gomerpedia Fun Fact
Did you know the song Under Pressure by David Bowie & Queen is about glaucoma? Bet you didn't!
Eye Eye, Captain!