Bon,
When MAC is diagnosed, the next step is to test and see which drugs it is susceptible to. Apparently your test showed Dr Swenson that you need to take both azithromycin and ethambutol. If you trust him with your care, don't you think it is wise to follow his advice?
Perhaps if you are really nervous, you could ask to have your vision checked every 2 months to earlier detect any changes?
Sue