Sheep have panoramic vision of 330°–360° and binocular
vision of 25°–50°. They are thought to have colour
vision and are able to distinguish between a variety of
colours: black, red, brown, green, yellow and white
(Alexander and Shillito, 1978). They have no accommodation,
so must lift the head to see distant objects. This
also means that they are unable to judge depth.
Sheep eyes possess very low hyperopia with little
astigmatism. Such physiological optics are likely to produce
a well-focused retinal image of objects in the middle
and long distance (Piggins, et al., 1996).
Sight is a vital part of communication and when
sheep are grazing they maintain visual contact with
each other (Crofton, 1958; Kilgour, 1977).
Each sheep throws its head to check the position of the other sheep.
This constant monitoring is probably what keeps the
sheep in a mob as they move along grazing.
Psychological stress induced by isolation is reduced
if sheep are provided with a mirror, indicating that the
sight of other sheep has stress-reducing properties
(Parrott, 1990).
http://animalbehaviour.net/JudithKBlackshaw/JKBlackshawCh3b.pdf
