Deer, as Olly said, it's also possible he's suffering from overly dry eyes. Did the neuro check his eyes, or was it just his answer to a question?
It seems from the PALS here that it isn't a common issue, so it may be an issue with a helpful treatment. For instance, if you notice it happens in the AM and PM when you wash his face is it possible it's a reaction to the soap you use?
Is it only happening in one room in the house, such as the bedroom? Is he on a bipap that could be irritating his eyes (mine water from my bipap for instance)
You'll notice that doctors are quick to lump everything as being ALS related, and it's just not always the case.