Buzzards for instance have distance vision 6 to 8 times better than ours, part of this is a result of the lens shaped central fovea which acts something like a times two magnifying lens. It is strongly supplied with blood vessels and is thought to help keep the retina well supplied with nutrients. Like us, birds have a small blind spot where the optic nerve meets the retina. There are two sorts of light receptors in the birds eye. They are called 'rods' and 'cones'.
Rods are better for night vision because they are sensitive to small quantities of light.
However as it is the cones that allow us to distinguish between different colours of light they are more important to colour orientated animals such as birds. Also there can be as many as 150 rods connected to a single nerve cell, this increases its sensitivity but reduces its definition, i.e. things look blurry. Cones can be as few as one or two per nerve cell, this works the opposite way making them less sensitive but more accurate for detail. Which is good during the daylight. Cones come in different flavours depending on which pigment they contain, different pigments detect different colours.