Xalatan and optic nerve

My mother is currently using Alphagan-P to lower her IOP. Her doctor has recommended that she switch to Xalatan or add it as a second drop at bedtime. I want to be especially cautious given that she is monocular and 90% of her optic nerve is damaged ( she seem to be progressively losing her perpheral vision despite an IOP of 13-17 ), and she has some macular degenerative problems. I understand with Xalatan, there could potentially be macular side effects. I would appreciate it if anyone has used Xalatan or Alphagan-P to comment on side effects that they may have experienced or efficacy and also if anyone may have some insight or perhaps personal experience related to this. I would be so very, very thankful for your help.