Definitely looks like a parasite and nematode seems a good guess but I'm not really qualified to verify.
I'd never heard of any such thing in reptiles either but a little googling brought me to an old article on a nematode that infects the eyes of
N. natrix http://www.cabdirect.org/abstracts/19690801825.html. And no, I don't have the article itself.
Interesting (and creepy!) whatever it is.