Nuisances for the viewers left out of formats (5)
I believe the answer is:
Here is my best explanation:
'formats' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how one could define the other.
I can't explain the rest of the clue.
(Other definitions for styes that I've seen before include "gatherings", "Problems seeing", "They make it difficult to see", "Pig pens", "Eyesores", "Eye infections", "Eye troubles", "Swellings" and "Eyelid swellings".)