The human eye
The pupil is the central transparent area (showing as black). The greenish-brown area surrounding it is the iris. The white outer area is the sclera, the central transparent part of which is the cornea.

Schematic diagram of the human eye.

The pupil is the variable-sized, black circular or slit shaped opening in the center of the iris that regulates the amount of light that enters the eye.^[1] It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. The iris of my eye. ... The iris of my eye. ... The human iris The iris is the green/grey/brown area. ... Schematic diagram of the human eye. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... Image File history File links Schematic_diagram_of_the_human_eye_en. ... Image File history File links Schematic_diagram_of_the_human_eye_en. ... The human iris The iris is the green/grey/brown area. ... It has been suggested that this article or section be merged with Electromagnetic radiation. ... A human eye. ... Biological tissue is a collection of interconnected cells that perform a similar function within an organism. ...

Comparative anatomy

In humans and many animals (but few fish), the size of the pupil is controlled by involuntary constriction and dilation of the iris in order to regulate the intensity of light entering the eye. This is known as the pupillary reflex. In normal room light, a healthy human pupil has a diameter of about 3-4 millimeters, in bright light, the pupil has a diameter of about 1.5 millimeters, and in dim light the diameter is enlarged to about 8 millimeters. Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. ... Animalia redirects here. ... A giant grouper at the Georgia Aquarium Fish are aquatic vertebrates that are typically cold-blooded; covered with scales, and equipped with two sets of paired fins and several unpaired fins. ... The human iris The iris is the green/grey/brown area. ... It has been suggested that this article or section be merged with Electromagnetic radiation. ... In medicine, pupil constriction (also known as the pupillary reflex) is reduction of pupil size. ...

The shape of the pupil varies between species. Common shapes are circular or slit-shaped, although more convoluted shapes can be found in aquatic species. The reasons for the variation in shapes are complex; the shape is closely related to the optical characteristics of the lens, the shape and sensitivity of the retina, and the visual requirements of the species. In biology, a species is one of the basic units of biodiversity. ... A circular may be: the adjective form of circle an advertisement which is circulated a Pastoral letter, Encyclic, or Papal bull that is circulated between churches a circular argument is a term for a type of logical fallacy where the very thing that is trying to be proved is assumed... Animal environments are classified as either aquatic (water), terrestrial (land), or amphibious (water and land). ... Human eye cross-sectional view. ...

Slit-shaped pupils are found in species which are active in a wide range of light levels. In strong light, the pupil constricts and is small, but still allows light to be cast over a large part of the retina.

The orientation of the slit may be related to the direction of motions the eye is required to notice most sensitively (so a vertical pupil would increase the sensitivity of the eyes of a small cat to the horizontal scurrying of mice). The narrower the pupil, the more accurate the depth perception of peripheral vision is, so narrowing it in one direction would increase depth perception in that plane.^[2] Animals like goats and sheep may have evolved horizontal pupils because better vision in the vertical plane may be benficial in mountainous environments.^[3] Peripheral vision is a part of vision that occurs outside the very center of gaze. ...

Ground dwelling snakes, such as boas, pythons and vipers, have vertical slit-shaped pupils to help them hunt prey on the ground while tree snakes have circular pupils. Small cats and foxes also have slit shaped pupils while lions and wolves have round pupils even though they are in the same respective families. Some hypothesize that this is because slit pupils are more beneficial for animals that hunt small prey than large prey.^[4] Families Acrochordidae Aniliidae Anomalepididae Anomochilidae Atractaspididae Boidae Bolyeriidae Colubridae Cylindrophiidae Elapidae Hydrophiidae Leptotyphlopidae Loxocemidae Pythonidae Tropidophiidae Typhlopidae Uropeltidae Viperidae Xenopeltidae Snakes are cold blooded legless reptiles closely related to lizards, which share the order Squamata. ... Boa Kwon (born November 5, 1986 in Guri, Gyeonggi-do, South Korea) is a South Korean singer, commonly known by her stage name BoA. She is an active singer in both South Korea and Japan. ... Genera Aspidites Antaresia Apodora Bothrochilus Leiopython Liasis Morelia Python Python is the common name for a group of non-venomous constricting snakes, specifically the family Pythonidae. ... Subfamilies Crotalinae (Pit Vipers) Viperinae (Vipers) The Viperidae family is made up of two subfamilies: Crotalinae (Pit Vipers) Viperinae (Vipers) Categories: Stub | Snakes ... Cats may refer to: Felines, members of the animal family Felidae The domesticated animal, cat The musical, yeah right, I bet that this was really dumb. ... A red fox The foxes comprise 23 species of omnivorous canids, found worldwide. ... Binomial name Panthera leo (Linnaeus, 1758) The Lion (Panthera leo) is a mammal of the family Felidae. ... Binomial name Canis lupus Linnaeus, 1758 Wolf redirects here. ...

When an eye is photographed with a flash, the iris cannot close the pupil fast enough and the blood-rich retina is illuminated, resulting in the red-eye effect. This article or section does not adequately cite its references or sources. ... A photographic flash is a device that produces a flash of light required for indoor or other low light conditions. ... Human eye cross-sectional view. ... The red-eye effect on a human. ...

Constriction of the pupil

The pupils of sheep and goats are horizontal almost rectangular ovals.

When bright light is shone on the eye, it will automatically constrict. This is the pupillary reflex, which is an important test of brainstem function. Furthermore, the pupil will dilate if a person sees an object of interest. Image File history File linksMetadata The_number_of_the_beast. ... Image File history File linksMetadata The_number_of_the_beast. ... Species See text. ... Species See Species and subspecies The goat is a mammal in the genus Capra, which consists of nine species: the Ibex, the West Caucasian Tur, the East Caucasian Tur, the Markhor, and the Wild Goat. ... In medicine, pupil constriction (also known as the pupillary reflex) is reduction of pupil size. ... The brain stem is the stalk of the brain below the cerebral hemispheres. ...

The oculomotor nerve, specifically the parasympathetic part coming from the Edinger-Westphal nucleus, terminates on the circular iris sphincter muscle. When this muscle contracts, it reduces the size of the pupil. The oculomotor nerve () is the third of twelve paired cranial nerves. ... Anatomy and Physiology of the A.N.S. In contrast to the voluntary nervous system, the involuntary or autonomic nervous system is responsible for homeostasis, maintaining a relatively constant internal environment by controlling such involuntary functions as digestion, respiration, and metabolism, and by modulating blood pressure. ... The Edinger-Westphal nucleus is the accessory parasympathetic nucleus of the oculomotor nerve, supplying the constricting muscles of the iris. ... The Iris sphincter muscle is a muscle of the human body. ...

Certain drugs cause constriction of the pupils, such as heroin. Other drugs, such as alcohol, cause pupil dilation. Heroin ((INN) Diacetylmorphine, (BAN) diamorphine) is a semi-synthetic opioid. ... Functional group of an alcohol molecule. ...

Another term for the constriction of the pupil is miosis. Substances that cause miosis are described as miotic. Miosis should not be confused with meiosis, the cellular division process involved in sexual reproduction. ... A miotic substances causes the constriction of the pupil of the eye ...

See also

• Dilated fundus examination
• Eye contact
• Horner's syndrome
• Mydriasis
• Synechia

Dilated fundus examination (DFE) is diagnostic procedure that employs the use of mydriatic eye drops to dilate or enlarge the pupil in order to obtain a better view of the internal surface of the eye (i. ... Eye contact is the event when two people look at each others eyes at the same time[1]. It is a form of nonverbal communication, and can be an intense or emotional occurrence or a soon-forgotten event. ... Horners syndrome is a clinical syndrome caused by damage to the sympathetic nervous system. ... // Mydriasis is an excessive dilation of the pupil due to disease or drugs. ... In medicine, synechia refers to an adhesion, usually involving the iris (see article below) but also within the uterus as in Ashermans syndrome. ...

Additional images

Iris, front view. Image File history File links Gray878. ...