Eagle eye
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The eagle eye is among the sharpest in the animal kingdom, with an eyesight estimated at 4 to 8 times stronger than that of the average human.[1] Although an eagle may only weigh 10 pounds (4.5 kg), its eyes are roughly the same size as those of a human.[1] Eagle weight varies: a small eagle could weigh 700 grams (1.5 lb), while a larger one could weigh 6.5 kilograms (14 lb); an eagle of about 10 kilograms (22 lb) weight could have eyes as big as that of a human who weighs 200 pounds (91 kg).[1] Although the size of the eagle eye is about the same as that of a human being, the back side shape of the eagle eye is flatter. Their eyes are stated to be larger in size than their brain, by weight.[2] Color vision with resolution and clarity are the most prominent features of eagles' eyes, hence sharp-sighted people are sometimes referred to as "eagle-eyed". Eagles can identify five distinctly colored squirrels and locate their prey even if hidden.[3]
In addition to eagles, birds such as
Eye anatomy and physiology
The outer most region of the eye is the cornea; light passes through the cornea first. Light is then refracted when passed through the cornea given its curved convex shape. "The image formed by the cornea is upside down and reversed from right to left."(Journey N, 1997–2019) The layers of the cornea in raptors include: the Anterior corneal epithelium, Anterior limiting lamina (Bowman's layer), Substantia propria (stroma comprising the majority of corneal thickness),Posterior limiting lamina (Descemet's membrane) Posterior epithelium (endothelium).[4]
The iris in eagles appears yellow and functions similarly to the iris in humans. The iris contracts and dilates to control the amount of light received by the retina. The muscles of the iris "striated muscle, smooth muscle, and a myopepithelial dilator muscle" Tucker, V. A. (2000–12) when contracted change the appearance of the pupil size. Eagles have large transparent lenses that have the ability to change shape. The purpose of the lens being able to change shape is so eagles can quickly focus on an object with accuracy. The sclera is made of approximately 15 small bones which give the eye its shape and function to protect the inner structures of the eye. The ciliary muscles originate at the sclera and are located within the ciliary body. These muscles are striated and function to change the shape of the lens.
An eagle's
Eagles have a highly developed sense of sight which allows them to easily spot prey. Eagles have excellent 20/5 vision compared to an average human who only has 20/20 vision. This means eagles can see things from 20 feet (or 6 meters) away that we can only see from 5 feet (or 1,5 meters) away. Beginning with their cranial structure, eagles have fixed eye sockets that are "angled 30 degrees from the midline of their face."
Eagles have upper and lower eyelids, the bottom lid is more mobile and gives the appearance of the eyelid blinking from bottom to top. Inside the eyelids are made up of connective tissue called fibroelastic plate (tarsus) that function to support the outer eyelid and give it shape. On the eyelids are small hair like feathers called filo-plumes that are comparable to human eyelashes. Eagles have a third eyelid also known as a
Most eagles have excellent vision. Generally, eagles do not suffer from
Eagle Species
Wood (1917), The Fundus Oculi of Birds, Especially as Viewed by the Ophthalmoscope: A Study in Comparative Anatomy and Physiology, describes eagle eye anatomy in detail:
- "fundus is dark reddish-brown, the lower half changing to a dull orange-red. The whole eyeground is covered with choroidal capillaries, and dotted over with brown pigment grains, giving it a rough, granular appearance. A gray sheen pervades the upper part of the fundus. On the temporal side and some distance from the upper end of the optic nerve is a brilliant, white, round dot surrounded by a small, light-green reflex ring, which is itself enclosed in a very brilliant, narrow green ring—the muscular region. On the nasal side of the disc, and on a level with this macula is another area, of a gray color, surrounded by a fan-shaped, luminous reflex. The optic nerve-entrance is distinctly white, and along its center is strewn a large number of minute pigment dots. The outer margin of the disc is bordered with black pigment, as if a shadow were cast upon it by the pecten. In this regard and in some others, this fundus resembles the eyeground of the sea eagle."[13]
- "White-bellied sea eagle (Haliaeetus leucogaster). The coloration of the eyeground is mostly dull-brown, the lower quadrants of the field being covered with dull, orange-red capillaries evidently choroidal. The optic disc is a long white oval, whose center is tinted with orange and covered with tiny pigment dots. The papillary margins are white bordered with black pigment. The upper half of the fundus is covered by a mass of dull gray dots. There is a well defined reflex near both maculae, each similar in position to that seen in the kestrel. These areas are evidently very sensitive to light, as the bird becomes very fidgety and irritable when the reflected rays from the mirror are thrown directly on one or other fovea. The pecten is very large and comes well forward towards the posterior surface of the lens. Both extremities of the organ are clearly visible through the ophthalmoscope. There are very opaque nerve fibers to be seen in any part of the eyeground."[14]
References
- ^ a b c d e f Grambo 2003, p. 11.
- ^ a b c d e "Vision: An In-depth Look at Eagle Eyes". Journey North. Arboretum, University of Wisconsin-Madison. Retrieved 11 December 2020.
- ^ a b c Dudley 1997, p. 10.
- ^ "Raptor Ophthalmology: Anatomy of the Avian Eye". LafeberVet. 2014-12-10. Retrieved 2020-12-08.
- ^ Boothe 2001, p. 235.
- PMID 11076738.
- ^ a b "What is eagle eye vision?". All About Vision. Retrieved 2020-12-07.
- ^ a b Hutchinson & Silliker 2000, p. 34.
- ^ Potts & Ueblacher 2006, p. 16.
- ^ Potts & Ueblacher 2006, pp. 11–13.
- ^ "A Closer Look at the Fascinating World of Bird Eyelids". Buffalo Bill Center of the West. 2016-02-29. Retrieved 2020-12-07.
- ^ "Bald Eagle's Eyesight and Hearing - American Bald Eagle Information". www.baldeagleinfo.com. Retrieved 2020-12-07.
- ^ Wood 1917, pp. 90-.
- ^ Wood 1917, pp. 91.
General
- This article incorporates text from this source, which is in the public domain: Wood's "The Fundus Oculi of Birds, Especially as Viewed by the Ophthalmoscope: A Study in Comparative Anatomy and Physiology" (1917)
Bibliography
- Boothe, Ronald G. (16 November 2001). Perception of the Visual Environment. Springer. pp. 235–. ISBN 978-0-387-98790-3.
- Dudley, Karen (1997). Bald Eagles. ISBN 9780919879942.
- Grambo, Rebecca L. (14 December 2003). Eagles. Voyageur Press. ISBN 978-0-89658-363-4.
- Hutchinson, Alan E.; Silliker, Bill (1 April 2000). Just Eagles. Willow Creek Press. pp. 34–. ISBN 978-1-57223-277-8.
- Potts, Steve; Ueblacher, Sigrid Noll- (2006). Wildlife of North America. Capstone. p. 11–. ISBN 9780736884839.
- Wood, Casey Albert (1917). The Fundus Oculi of Birds, Especially as Viewed by the Ophthalmoscope: A Study in Comparative Anatomy and Physiology (public domain ed.). Lakeside Press. pp. 90–.
- Carvalho, Clarissa Machado de, Rodarte-Almeida, Ana Carolina da Veiga, Santana, Marcelo Ismar Silva, & Galera, Paula Diniz. (2018). Avian ophthalmic peculiarities. Ciência Rural, 48(12), e20170904. Epub December 6, 1928.https://doi.org/10.1590/0103-8478cr20170904
- Bald Eagle's Eyesight and Hearing - American Bald Eagle Information, www.baldeagleinfo.com/eagle/eagle2.html.
- "Eagle Biology." National Eagle Center, www.nationaleaglecenter.org/learn/biology/.
- "Facts About Eagle Eyesight: What Is Eagle Vision And How Do Hawkeye See?" ImproveEyesightHQ.com, www.improveeyesighthq.com/eagle-eyesight.html.
- Hay, Anne. "A Closer Look at the Fascinating World of Bird Eyelids." Buffalo Bill Center of the West, 11 May 2020, centerofthewest.org/2016/02/29/eyelids-like-bird/.
- "Raptor Ophthalmology: Anatomy of the Avian Eye." LafeberVet, 26 Oct. 2020, lafeber.com/vet/raptor-ophthalmology-anatomy-of-the-avian-eye/.
- Team, All About Vision Editorial. "What Is Eagle Eye Vision?" All About Vision, All About Vision, 7 Dec. 2020, www.allaboutvision.com/resources/eagle-vision/.
- Tucker, V. A. (2000–12). "The deep fovea, sideways vision and spiral flight paths in raptors". The Journal of Experimental Biology. 203 (Pt 24): 3745–3754. PMID11076738.