The human eye contains one primary vein that carries blood away from the eye. There are also many smaller veins, known as capillaries, branching throughout the eye, supplying oxygen and nutrients to the tissues. These smaller veins are too small to be seen with the naked eye.
Note: The question may refer to the visible red veins often seen on the white of the eye. These are not true veins, but rather dilated blood vessels called conjunctival vessels, which can become enlarged due to several factors, including allergies, eye strain, and infections.
