First of all I want to preface all of this by mentioning that it really depends how vision isn't working, because there are different levels and causes for blindness, not all of them even a problem with the eyes.

But let's say it's total blindness because the eyes are "not working", you got a face full of laser and the nerves behind your pupils are fried. They'll detect zero brightness, not because there is no brightness, but because they're broken and can't send a signal. They failed in the "off" position, so to speak. If you "SEE darkness", that was invented by your brain, and it's mostly an artifact of still remembering having vision pretty recently. Spend enough time without vision and your brain will restructure itself to make better use of those resources.

Again though, how are your eardrums different? Your eyes detect fluctuations in the EM field, your eardrums detect fluctuations in a sound medium, both detections get passed as electrical signals to the brain for further processing.