This could be unrelated to your dad's ALS... has he been screened for glaucoma recently? The regular kind of glaucoma is usually pain free, but narrow angle glaucoma does cause intense pain. Does he see halo's around lights or have blurry vision? I myself have narrow angle glaucoma, was diagnosed in my late 40's. It was discovered when I was dissatisfied with an eye doctor trying to convince me that my problems were due to allergies coupled with migraine headaches. I went to a glaucoma specialist, and it was diagnosed. This is not common, but since it is also one of those diseases that are frequently mis-diagnosed, just like MND, I thought I'd chime in.
BTW, eye drops for glaucoma are useless for narrow or closed angle glaucoma, however there is laser surgery that is quick, and almost painless. I was able to drive immediately afterwards, and even did not have to go without eye makeup during or after the procedure. If your dad is far sighted (can't see close up) and has brown eyes he would fit the profile for narrow angle better than someone who is nearsighted and has lighter colored irises.
Also........ as for dry eye drops; if regular moisture drops are not effective, look for moisture gel drops. They can be found over the counter, just look at ingredients and make sure that mineral oil or other petroleum products aren't an ingredient.
take care, :smile:
