Carol Aldrich first noticed a slight tremor in her right hand when she was in her early 50s. Working for an optometrist in Port Townsend, Wash., a picturesque town on the Olympic Peninsula, Aldrich routinely performed delicate work with her fingers—replacing broken eyeglass lenses and repairing frames. At least initially, her tremor would come and go, leaving her sometimes unable to manage tiny screws and fragile settings. “I just thought I had had too much coffee,” the mother of three recalls.