Most of the Owl species are nocturnal and have become well adapted to night vision which helps them to hunt their prey in dark.
The better night vision is due to the following reasons:
A lot more rods in the retina of their eyes. The rods are the photosensitive pigments found in the eyes. these rods are adapted to seeing in the dark. Hence, the owls have a better vision at night.
Large cornea helps the owls to pick up even the slightest amount of light present.
The magical layer of Tapetum lucidum. This layer is like a mirror and reflects back the light and helps in a better vision.
However, some diurnal owls do not have a good vision in dark conditions and instead, are better adapted for hunting during the day.