Could ortho k lenses cause blindness?

Unlikely: Ortho k is a sort of a way for optoms to get into the eye power changing game which really is dominated by the more effective lasik. It puts a hard contact lens that is too flat onto the eye, pushing it back to remold it. This is of course a bit uncomfortable. There is a tiny risk of corneal breakdown and/or infection but monitoring is generally good. Lasik is a much better option.