Pecten oculi
Encyclopedia
The pecten or pecten oculi is a comb-like structure of blood vessel
s belonging to the choroid
in the eye
of a bird
. It is non-sensory and is a pigment
ed structure that projects into the vitreous body from the point where the optic nerve
enters the eyeball. The pecten is believed to both nourish the retina
and control the pH
of the vitreous body. It is present in all birds and some reptile
s.
In the vertebrate eye, blood vessels lie in front of the retina
, partially obscuring the image. The pecten helps to solve this problem, lifting the blood vessels away from the retina and leading to the extremely sharp eyesight of birds such as hawk
s. The pigmentation of the pecten is believed to protect the blood vessels against damage from ultraviolet
light. The structure varies across birds and is conical in the kiwi, vaned in the ostrich and pleated in most other birds.
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s belonging to the choroid
Choroid
The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye , while in the outlying areas it narrows to 0.1 mm...
in the eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
of a bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
. It is non-sensory and is a pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
ed structure that projects into the vitreous body from the point where the optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...
enters the eyeball. The pecten is believed to both nourish the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
and control the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of the vitreous body. It is present in all birds and some reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s.
In the vertebrate eye, blood vessels lie in front of the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
, partially obscuring the image. The pecten helps to solve this problem, lifting the blood vessels away from the retina and leading to the extremely sharp eyesight of birds such as hawk
Hawk
The term hawk can be used in several ways:* In strict usage in Australia and Africa, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks,...
s. The pigmentation of the pecten is believed to protect the blood vessels against damage from ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light. The structure varies across birds and is conical in the kiwi, vaned in the ostrich and pleated in most other birds.
External links
- Electron microscopy photos of the pecten in the black kite (Milvus migrans)