We assume that owls, being primarily a bird of the night, must have superior eyesight. Actually, they can see no better than humans or cats at night. What makes them especially talented at obtaining food after dark is their hearing.
While owls do see well in dim light, it is their ears that make them such great hunters at night. Owls have large ear openings just behind their eyes. With special feathers as part of their facial disks, which act like sound funnels as well as asymmetrical ear locations, they can hear the slightest rustle of sound of an insect or a mouse/vole under leaves or snow.