The pecten or pecten oculi is a
comb-like structure of
blood vessels belonging to the
choroid in the
eye of a
bird. It is a non-
sensory,
pigmented structure that projects into the
vitreous humor from the point where the
optic nerve enters the
eyeball.[1] The pecten is believed to both nourish the
retina and control the
pH of the vitreous body.[2] High levels of
alkaline phosphatase activity in the pecten oculi have been linked to the transport of nutrient molecules from the highly vascularized choroid into vitreous and retinal cells, thus nourishing the eye.[3] It is present in all birds and some
reptiles.[4]
In the
vertebrate eye, there are blood vessels in front of the retina, partially obscuring the image. The pecten helps to solve this problem by greatly reducing the number of blood vessels in the retina and leading to the extremely sharp eyesight of birds such as
hawks.[5] The pigmentation of the pecten is believed to protect the blood vessels against damage from
ultraviolet light.
Stray light absorption by melanin granules of pecten oculi is also considered to give rise to small increments in temperature of pecten and eye; this may offer increased metabolic rate to optimize eye physiology in low temperatures at high-altitude flights.[6] The structure varies across bird
species and is
conical in the
kiwi, vaned in the
ostrich and
pleated in most other birds.[7]
^Walls (1942), The Vertebrate Eye and its Adaptive Radiation, Hafner Publishing,
ISBN0-02-854430-7
^Kiama, S. G.; Maina, J. N.; Bhattacharjee, J.; Weyrauch, K. D. (2001). "Functional morphology of the pecten oculi in the nocturnal spotted eagle owl (Bubo bubo africanus), and the diurnal black kite (Milvus migrans) and domestic fowl (Gallus gallus var. domesticus): a comparative study". Journal of Zoology. 254 (4): 521–528.
doi:
10.1017/s0952836901001029.
^Kiama, S G; Bhattacharjee, J; Maina, J N; Weyrauch, K D (December 1994), "A scanning electron microscope study of the pecten oculi of the black kite (Milvus migrans): possible involvement of melanosomes in protecting the pecten against damage by ultraviolet light", Journal of Anatomy, 185 (Pt 3): 637–642,
PMC1166670,
PMID7649799