Negative power means you have myopia or short-sight. Ask the doctor to check your retina and intra-ocular pressure (IOP), and if they are normal you don’t have to worry. It is just that your eye is a little longer and so you need minus glasses so that the rays can get focused on your retina. You can use glasses or contact lenses, and if your eyes are healthy, you can get Lasik or Epilasik done. Have annual eye checkups.