Avian Eye Tunics

The Retina contains the vitreous humor.

The tunics have the same function in birds as mammals. However, there are some differences in structure. The sclera, the outermost layer, is reinforced by eleven to sixteen small bones forming the sclerotic ring in avians. The cornea is generally larger in mammals than in birds, in relation to the size of the eye, with nocturnal birds having larger corneas than diurnal birds.

The uvea is the middle tunic, which contains the choroid, tapetum lucidum, iris, and ciliary body (Internal Structures of the Avian Eye).

One major difference between the mammalian and avian retina is that the mammalian retina is vascularized, while the avian is not. The retina contains the fovea, which is the point of sharpest vision or highest resolution. In certain avian eyes, such as the hawk, there are two fovea. There is a central area across the retina with a fovea at each end. This allows the bird to see the horizon, while in flying position, without the movement of eye or neck muscles. The common buzzard has 1,000,000 cones per square millimeter of retinal surface as opposed to man, who contains 200,000.

Main Page