During development–and the younger the individual and the longer the period of time, the worse–extinguishing signals from one eye for any reason (congenital abnormality of the eye; very poor unilateral refracton; eye patch…) creates abnormal yoking (a “lazy” eye) and abnormal visual pathways. The damage can be permanent, and for this reason vision is corrected as early as possible in youngsters.
For an older individual, similar changes might occur but they would take much longer and be less permanent. Folks who are blinded in one eye in adulthood have substantially less change than those who are unilaterally blind from birth, but it can occur. I am not expert enough to tell you how long you would need to wear an eyepatch to create damage, or how long such damage might last.