High pressure in the eye has caused damage in the optic nerve. So after cataract surgery the visual outcome will depend on how much optic nerve is still functioning. Yes, it is a matter of concern. But we don't have options. Cataract removal is to be done after control of eye pressure. Vision after surgery will be guarded ( which you have to accept).

It means that the complete vision as expected is not guaranteed, and the prognosis is guarded, due to conditions of the Eye.

There could be damage to the nerve of the eye due to high pressure, which is generally irreversible.  That's why guarded prognosis is mentioned. Please consult any ophthalmologist online or offline,  so that all your doubts can be cleared in one go. 

Patient has both cataract and glaucoma. So due to higher eye pressure, optic nerve can be compressed which may lead to permanent changes in visual acuity. So that can't be reversed even with cataract surgery And even cataract surgery itself, in this high pressure, needs some extra care and precautions. So they have written guarded progny.