Diagnosis. Glaucoma is when the eye pressure leads to progressive nerve damage over time. If untreated, it leads to irreversible vision loss and blindness. Cataract is when the lens inside the eye becomes cloudy and affects vision adversely. It is treatable by surgery and completely reversible.
Different diseases. Glaucoma is a disease where the pressure in the eye damages the optic nerve resulting in loss of vision if untreated. This is usually a slow process, but acute angle closure glaucoma is a sudden loss. Cataract is a clouding of the natural lens and treatment is surgical replacement with a clear lens when the vision is reduced to the point reading/driving is difficult.