Pectin is the most puzzling organ of the eye of a few reptiles and all birds (except kiwi). It is a highly vascular, pigmented, folded, and comb-like structure. It projects into the vitreous humour from the retinal surface ventral to the blind spot. It is soft and almost rectangular.
Functions of Pectin
Several functions have been assigned to the Pectin:
1. Probably its main function is to bring oxygen and nourishment to the retina, which is vascular in birds. It allows exchange of materials between the blood stream and the vitreous humour.
2. It is possible that the irregular shadow cast by this organ on the retina helps in detection of movements of an object. The function is supported by the observation that it is larger and much folded in predatory birds, and is small and smooth in nocturnal birds.
3. It may in some way be connected with accommodation. It probably regulates liquid pressure inside the eye which is changed by the change in the position of lens during accommodation. Last two functions arc yet to be confirmed.