at the same time. also notice the distance between your eyes and the sheet music. you will want to remember this distance and the level of the music to share with and eye doctor if you need to see one.
when you are secure in where your music needs to be, you can then attend to your vision issues with a professional. make sure that you tell any professional that you are a musician and you need help to see the music better. show them how you move your head when you play and how far away from the music you expect to be most times. this will be really helpful 