I can't comment on the medical implications of air pressure combined with intraocular pressure in the eye. That said I believe the pressure in the eye changes very slowly while the pressure around us can change quite quickly, like during an airplane trip. I understand that airline practice is to let the cabin pressure drop as the plane goes higher and higher until you reach 10,000 feet. After 10,000 feet the plane holds that pressure above what is outside the plane. That is why you get get the ear popping effect on ascent and descent during that 10.000 foot elevation change. And, some mountains can be higher than 10,000 feet and the pressure drop around you will be even more than if you are just taking a plane ride.
So for sure during a plane trip or going up high mountains will certainly change the pressure differential from outside the eye to inside the eye, but I have no idea what medical impact that has if any...
First of all the intraocular pressure (IOP) changes constantly throughout the day just like blood pressure and blood sugar. 20-21 are considered normal. So to have glaucoma you would need other things present which your eye doctor should have discussed with you: abnormal visual field, advanced cupping of the optic nerve, a unusual type of glaucoma called low tension glaucoma, or extremely thin corneas or many blood related individuals with glaucoma. If you don't know these factors you should write them down and review next time you are in to see your optometrist or ophthalmologist Almost all ophthalmologists do not put restrictions on visiting the mountains. The biggest problem with higher altitudes are dry eyes.