Ive just found out that the words of "Peace O'er the World" (the eyeballs carol) are from the middle of the 1712 poem "Messiah" by Alexander Pope. I note that there is a version of the carol from Lancashire known as "Messiah".
Interesting that no more of the original words were used as they seem to be appropriate.

It is interesting that the phrase "from thick films shall purge the visual ray" seems to me to imply the old belief that the eyes sent out rays to achieve vision. In other words "remove cataracts so that the visual ray can get out of the eyes".