Thought you might want to check out this family web site: http://www.sundheim.com/http://www.sundheim.com/ He has the Snellen line listed & if I remember correctly his Snellen line follows Snellenberger.I have a few other sites I will send to you also.There has been much research in the Snellenberger/Snellen line theory.The people show up in records as Snellen, Snellin, Snelling, Snellings.So you might want to check it out.
The Snellens/Snellings listed on the above web site are not my Snelling family but I have ran into their records while doing my family research.I have never heard of any purposeful changing of the name spelling. Rather that the name was spelled as the person heard it being spoken. Keeping inmind that many of our ancestors did not write their names until they went to school. So depending on how they said their name, the teacher would spell it.Like my Snelling family in Missouri, with an accent I can see how the name would sound like Snellen. I find my Snelling name spelled all of the ways listed above.Infact their is a direct line from my Snelling ancestor that still spells their name today as Snellen. And the Snellen/Snellenberger line is a completely different family line (we think). So that line may very well have started with a different spelling entirely. I will check my files and see if any of your names show up there.
Keep me posted, I will be interested in what you find. This Snelling family line is my 'difficult family'.It has been the hardest to connect.