Hi! I'm an optometrist. There are usually no symptoms for glaucoma, which is why it's known as a "silent thief of sight." Dryness and irritation are not symptoms of glaucoma. It is usually suspected when your doctor looks inside your eye at the optic nerve and sees that the cup in the middle of the optic nerve looks larger than they think it should be and your eye pressure (measured with either the air puff test or little probe that quickly touches your eye) seems a higher than normal. There's also a machine called the OCT which can help to see if you might be suspect for glaucoma. The visual field test checks your side vision to see if there is functional damage from the glaucoma. Your doctor may monitor it and make it an official diagnosis if they see progression on any of these things (optic nerve, OCT, visual field).
There is one kind of high eye pressure (acute angle closure) that can lead to glaucoma that may be accompanied with redness and eye pain, but this is more rare and happens more quickly. Otherwise, most forms of glaucoma (normal tension and open angle glaucoma) are extremely slowly progressing and don't have any symptoms until it's too late, when lose your side vision and are left with tunnel vision.
Quadrant Eye uses some tests which can help to screen for glaucoma even when you have no symptoms. Thank you Quadrant Eye for making a higher quality online screening! I can't wait for the entire comprehensive eye exam to be available at home and reach more people who otherwise may not have easy or convenient access to a doctor's office on a regular basis.