Blank faces v. blurred faces

It's hard to gauge how much they actually understood. As I scanned the room I saw a sea of blank faces, expressionless, dotted with the occasional yawn and dozing head. It's hard to keep going during these times. My policy (no longer enforced) of not wearing my glasses during lectures perhaps needs to be reinstated. If it has to be a choice between blank faces and blurred faces, would the latter not be more desirable, from the lecturer's point of view? When you think you have done all you could to make a dry subject seem interesting, yet still failing, what more can you do? It is more than a little ironic that just yesterday I was given a certificate of merit in "teaching excellence". And less than 24 hours after that public acknowledgement of my "achievements" in teaching, I am feeling pretty damn low about my merits as a teacher, amongst other things.