Hi. I'm online and happy to answer your question today.
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Does your "blister" look something like this:
Let me see if the picture of the above link will post:
I can see it, but I'm not sure if you can. Click on the link if you can't see the picture.
Good. Does it look something like that?
It sounds like what your father has is called a pinguecula. This is a change in the skin around the eye (conjunctiva) from a lifetime's worth of exposure to sunlight. It is not a cancer. It also can become irritated and red at times.
Here is a link to a picture of a small pinguecula. You can find many other pictures by going to Google images:
This is link to a picture of a pterygium. As you can see one of the major differences between a pterygium and a pinguecula is that a pterygium grows across the clear part of your eye (cornea):
If you are bothered by your pinguecula it can be surgically removed fairly easily by your ophthalmologist using local anesthesia. One word of caution however.....they have the nasty habit of growing back, sometimes with a vengeance.
Does this make sense to you?
It will not cause him any harm and it can be left alone. If it gets red have him, or the staff, use natural tears 3-4 times/day to soothe it. Visine will just make things worse and should be avoided.
That is not correct. They do not go away by themselves, but they rarely cause any difficulties.