Dear Krissy,
If your father needs to be on those medications, he has glaucoma. By definition, ocular hypertension is increased eye pressure WITHOUT visual loss. If the vision loss is from glaucoma and it is progressing, then more aggressive treatment should be pursued.
Although "normal" pressure is usually under 22 (which varies by about 5 points through the day) there are some people who need their eye pressure to be even lower due to the fragility of their optic nerves.
If he were my patient, I would do a serial tonometry to see how high his pressure gets through a time period...usually every 2 hours it is checked.
I would check his blood pressure as some people have low blood pressure and the perfusion of blood/oxygen to the eye is poor and it progresses with visual loss like glaucoma. I would encourage him to eat healthy and exercise every day. If his blood pressure is under 110/70, he needs to get it up (eat salty foods).
Laser procedures can be good but 50% of them no longer work after 5 years. Filtering surgical procedures are indicated sometimes as well.
I hope your Dad is seeing an eye MD ophthalmologist. For some reason some state legislators have allowed non-MD practitioners to "prescribe" glaucoma drops and patients don't know that they are not being treated by an MD.
Another thought...ask if your Dad has any other eye condition as this is the age when cataracts and macular degeneration can develop.
listen to berrywoo - good advice
If your father is suffering from field defects the ocular hypertension has more than likely turned into glaucoma. He should be under the care of a glaucoma specialist. You can find one at www.aao.org.
Currently, for priimary open angle glaucoma, there is no cure. Also, once field defects occur it normally signifies optic nerve damage which is irreversible at this time. However, there are treatments out that may help your father preserve what vision he has left. Again, get in contact w/ an ophthalmologist who specializes in glaucoma as s/he will be best equiped to deal with your father's care. Take care.