The retina of bird is the innermost layer and is sensory in nature. It is supplied by optic nerve projecting through the retina at they eye is a prominent vascular, pigmented fan shaped, vascular ridged plates called pectin, which protrudes, from the region of the blind spot, where the optic nerve enters.
This structure belongs to the choroids layer and extends in to the vitreous humor in the middle of the eye towards the ends with which it is connected by a transverse ligament.
The function of pectin is not definitely known although it is regarded that it may supply the lens with nutrient or may help to stabilize the pressure of the fluid within the eye. However, it is quite possible that it is associated with the remarkable power of optic accommodation found in birds.