I suffered a concussion in the past and my vision is deteriorating. Could that be causing my balance to get worse?
Vision is an essential part of the balance system. If you are noticing that your vision is changing and you are finding it hard to read it seems reasonable to visit your optometrist and have your eyes checked.
In addition to that, given your history of concussion, it would probably be a good idea to see a neuro-ophthalmologist or a neuro-optometrist to assess how your eyes are working together and how you are processing visual information as these are also contributing factors to human balance. You can learn more about how these professionals can help here: https://www.balanceanddizziness.org/pdf/Health-Professionals.pdf
Also, please make sure you keep your vestibular therapist informed of your vision changes, as well as any falls you may experience. Your rehabilitation programme should continue to address these issues.