How do veterans deal with vision loss after combat?

With difficulty. Military and veterans hospitals have a staff of assistants that can help veterans deal with vision loss (and other losses). There are unfortunately many of these so they are getting better at it. Civilian agencies are also present to assist those who have visual impairment.
Difficult adjustment. In addition to the VA, this website has some good information and resources: Multiple links are provided to assist. While on this page, one can also click on the Blinded Veterans Association for information about their programs and eligibility. Best wishes.