Eyes open or eyes closed? Sorry for the kidding, but even if you force the learner to sit through a slide till the end before allowing him to proceed, is that any guarantee that he learned better? Certainly not for adult learning. Best way is to make the content so engaging that the learner will not even try to skip anything.
Forcing can be done using the timeline: do not use the default playbar but a Next button appearing when the content is almost finished. That is the easiest way.