Most blind cave animals evolved from sighted surface dwellers (the only exception I can think of are a few species of worms, about the same level as a planarian, and those might also have evolved from similar creatures with eyespots).
Therefore, you need only an excuse for the eyes not to have been lost to evolution.
The simplest is for infrared vision to have gone much further than it has in most mammals. All humans can see a little into what's commonly called "infrared", at least long enough wavelengths to see the kind of weird vision that one sees in infrared photography (black skies, white leaves, etc.). This isn't long enough to see heat radiation, but you could easily handwave a population underground for many millennia to have evolved that level of IR vision.
They'd have eyeballs -- in fact, their eyes might be a good bit larger than ours (to gather more radiation, or to give good resolution with longer waves), but they'd be debilitated in daylight. Not only because it's too bright -- but because the reflected IR from the sun or other sources would be so unfamiliar they couldn't make sense or what they were seeing, even after their eyes adjusted enough not to be just a blinding pain.