Borderline on appropriateness from teacher
Strange blink patterns are not necessarily a sign of a need for glasses, one of my students has similar symptoms as part of Tourette's Syndrome - there are a myriad of other reasons what this could be a symptom of.  Having said that, asking the students how they are individually as they enter class may give some insight.

Beyond that, I would ask your supervisor or someone in administration first if something has already been documented about the potential condition the student may have.  If not, then it is your superior, the nurse or someone in administration that should be informed of your concerns, this will do 2 things:


save any potential embarrassment for you and the student.
provide evidence of you chasing-up the concern through official channels