Generally, dry macular degeneration progresses very slowly. No one disease is the same as the next person's. Hence it is impossible to tell each individual how rapidly their macular degeneration will progress.
Recently there have been studies that suggest that taking antioxidant vitamins will slow the natural progression of most patients' dry macular degeneration. Hence ophthalmologists recommend taking the antioxidant vitamins and get regular eye health checkups rather than worrying about how fast their disease may progress.