In most vertebrates and some mollusks the eye works by allowing light to enter it and project onto a light-sensitive panel of cells known as the retina at the rear of the eye, where the light is detected and converted into electrical signals, which are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris which regulates the intensity of the light that enters the eye. The eyes of cephalopods, ...

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Eye, Eye - Varieties of eyes, Eye - Evolution of eyes, Eye - Anatomy, Eye - Cytology, Eye - Acuity, Eye - Dynamic range, Eye - Adnexa and related parts, Eye - The orbit, Eye - Eyebrows, Eye - Eyelids, Eye - Eyelashes, Eye - Eye movement, Eye - Rapid eye movement, Eye - Saccades, Eye - Microsaccades, Eye - Vestibulo-ocular reflex, Eye - Smooth pursuit movement, Eye - Optokinetic reflex, Eye - Vergence movement, Eye - Accommodation, Eye - Diseases disorders and age-related changes

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Animals with compound eyes have a wide field of vision, allowing them to look in many directions. To see more, they have to move their entire head or even body. The visual system in the brain is too slow to process that information if the images are slipping across the retina at more than a few degrees per second (Westheimer and McKee, 1954). Thus, for humans to be able to see while moving, the brain must compensate for the motion of the head by turning the eyes. Another complication for vision in frontal-eyed animals is the developme ...

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Eye, Eye - Varieties of eyes, Eye - Evolution of eyes, Eye - Anatomy, Eye - Cytology, Eye - Acuity, Eye - Dynamic range, Eye - Adnexa and related parts, Eye - The orbit, Eye - Eyebrows, Eye - Eyelids, Eye - Eyelashes, Eye - Eye movement, Eye - Rapid eye movement, Eye - Saccades, Eye - Microsaccades, Eye - Vestibulo-ocular reflex, Eye - Smooth pursuit movement, Eye - Optokinetic reflex, Eye - Vergence movement, Eye - Accommodation, Eye - Diseases disorders and age-related changes

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There are many diseases and disorders that may affect the eyes. As the eye ages certain changes occur that can be attributed to solely the aging process. Most of these anatomic and physiologic processes follow a gradual decline. With aging, the quality of vision worsens due to reasons independent of aging eye diseases. While there are many changes of significance in the nondiseased eye, the most functionally important changes seem to be a reduction in pupil size and the loss of accommodation or focusing capability (presbyopia). The ar ...

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Eye, Eye - Varieties of eyes, Eye - Evolution of eyes, Eye - Anatomy, Eye - Cytology, Eye - Acuity, Eye - Dynamic range, Eye - Adnexa and related parts, Eye - The orbit, Eye - Eyebrows, Eye - Eyelids, Eye - Eyelashes, Eye - Eye movement, Eye - Rapid eye movement, Eye - Saccades, Eye - Microsaccades, Eye - Vestibulo-ocular reflex, Eye - Smooth pursuit movement, Eye - Optokinetic reflex, Eye - Vergence movement, Eye - Accommodation, Eye - Diseases disorders and age-related changes

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There are many diseases and disorders that may affect the eyes. As the eye ages certain changes occur that can be attributed to solely the aging process. Most of these anatomic and physiologic processes follow a gradual decline. With aging, the quality of vision worsens due to reasons independent of aging eye diseases. While there are many changes of significance in the nondiseased eye, the most functionally important changes seem to be a reduction in pupil size and the loss of accommodation or focusing capability (presbyopia). The ar ...

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Eye, Eye - Varieties of eyes, Eye - Evolution of eyes, Eye - Anatomy, Eye - Cytology, Eye - Acuity, Eye - Dynamic range, Eye - Adnexa and related parts, Eye - The orbit, Eye - Eyebrows, Eye - Eyelids, Eye - Eyelashes, Eye - Eye movement, Eye - Rapid eye movement, Eye - Saccades, Eye - Microsaccades, Eye - Vestibulo-ocular reflex, Eye - Smooth pursuit movement, Eye - Optokinetic reflex, Eye - Vergence movement, Eye - Accommodation, Eye - Diseases, disorders, and age-related changes

Read more here: » Eye: Encyclopedia II - Eye - Diseases, disorders, and age-related changes

Main articles: List of eye diseases and disorders and Ocular manifestations of systemic disease There are many diseases and disorders that may affect the eyes. As the eye ages certain changes occur that can be attributed to solely the aging process. Most of these anatomic and physiologic processes follow a gradual decline. With aging, the quality of vision worsens due to reasons independent of aging eye diseases. While there are many changes of significance in the nondiseased e ...

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Eye, Eye - Varieties of eyes, Eye - Evolution of eyes, Eye - Anatomy, Eye - Cytology, Eye - Acuity, Eye - Dynamic range, Eye - Adnexa and related parts, Eye - The orbit, Eye - Eyebrows, Eye - Eyelids, Eye - Eyelashes, Eye - Eye movement, Eye - Rapid eye movement, Eye - Saccades, Eye - Microsaccades, Eye - Vestibulo-ocular reflex, Eye - Smooth pursuit movement, Eye - Optokinetic reflex, Eye - Vergence movement, Eye - Accommodation, Eye - Diseases disorders and age-related changes

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The structure of the mammalian eye owes itself completely to the task of focusing light onto the retina. All of the individual components through which light travels within the eye before reaching the retina are transparent, minimising dimming of the light. The cornea and lens help to converge light rays to focus onto the retina. This light causes chemical changes in the photosensitive cells of the retina, the products of which trigger nerve impu ...

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Eye, Eye - Varieties of eyes, Eye - Evolution of eyes, Eye - Anatomy, Eye - Cytology, Eye - Acuity, Eye - Dynamic range, Eye - Adnexa and related parts, Eye - The orbit, Eye - Eyebrows, Eye - Eyelids, Eye - Eyelashes, Eye - Eye movement, Eye - Rapid eye movement, Eye - Saccades, Eye - Microsaccades, Eye - Vestibulo-ocular reflex, Eye - Smooth pursuit movement, Eye - Optokinetic reflex, Eye - Vergence movement, Eye - Accommodation, Eye - Diseases disorders and age-related changes

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When bright light is shone on the eye, it will automatically constrict. This is the pupillary reflex, which protects the retina from bright light, and is an important test of brainstem function. Also, the pupil will constrict if a person sees a thing or person which arouses anger or loathing. 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. Certain drug ...

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Pupil, Pupil - Dilation of the pupil, Pupil - Constriction of the pupil

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Visual acuity can be measured with several different metrics. Cycles per degree (CPD) measures how much an eye can differentiate one object from another in terms of degree angles. It is essentially no different from angular resolution. To measure CPD, first draw a series of black and white lines of equal width on a grid (similar to a bar code). Next, place the observer at a distance such that the sides of the grid appear one degree apart. If the grid is 1 meter away, then the grid should be about 8.7 millimeters wide. Finally, increas ...

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Eye, Eye - Varieties of eyes, Eye - Evolution of eyes, Eye - Anatomy, Eye - Cytology, Eye - Acuity, Eye - Dynamic range, Eye - Adnexa and related parts, Eye - The orbit, Eye - Eyebrows, Eye - Eyelids, Eye - Eyelashes, Eye - Eye movement, Eye - Rapid eye movement, Eye - Saccades, Eye - Microsaccades, Eye - Vestibulo-ocular reflex, Eye - Smooth pursuit movement, Eye - Optokinetic reflex, Eye - Vergence movement, Eye - Accommodation, Eye - Diseases disorders and age-related changes

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How a complex structure like the projecting eye could have evolved is often said to be a difficult question for the theory of evolution. Darwin famously treated the subject of eye evolution in his Origin of Species: To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible ...

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Eye, Eye - Varieties of eyes, Eye - Evolution of eyes, Eye - Anatomy, Eye - Cytology, Eye - Acuity, Eye - Dynamic range, Eye - Adnexa and related parts, Eye - The orbit, Eye - Eyebrows, Eye - Eyelids, Eye - Eyelashes, Eye - Eye movement, Eye - Rapid eye movement, Eye - Saccades, Eye - Microsaccades, Eye - Vestibulo-ocular reflex, Eye - Smooth pursuit movement, Eye - Optokinetic reflex, Eye - Vergence movement, Eye - Accommodation, Eye - Diseases disorders and age-related changes

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Dilation occurs when signals from sympathetic fibers (these fibres travel from the sympathetic trunk up to the face) cause the iris dilator muscles to contract. Damage to the sympathetic tract to the face (cranial nerve VII) results in Horner's syndrome, a symptom of which is excessive pupillary constriction (miosis) in one eye. This disparity in pupil size is termed anisocoria. The human pupil dilates if the person sees something (or someone) of interest or is aroused. Studies have shown that humans (especially females) are ju ...

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Pupil, Pupil - Dilation of the pupil, Pupil - Constriction of the pupil

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The retina contains two forms of photosensitive cells - rods and cones. Though structurally and metabolically similar, their function is quite different, though they are equally important to vision. Rod cells are highly sensitive to light allowing them to respond in dim light and dark conditions. These are the cells which allow humans and other animals to see by moonlight, or with very little available light (as in a dark room). However, they do not distinguish between colours, and have low visual acuity (a measure of detail). This is why th ...

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Eye, Eye - Varieties of eyes, Eye - Evolution of eyes, Eye - Anatomy, Eye - Cytology, Eye - Acuity, Eye - Dynamic range, Eye - Adnexa and related parts, Eye - The orbit, Eye - Eyebrows, Eye - Eyelids, Eye - Eyelashes, Eye - Eye movement, Eye - Rapid eye movement, Eye - Saccades, Eye - Microsaccades, Eye - Vestibulo-ocular reflex, Eye - Smooth pursuit movement, Eye - Optokinetic reflex, Eye - Vergence movement, Eye - Accommodation, Eye - Diseases disorders and age-related changes

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Belief in the evil eye is strongest in the Middle East, Asia and Europe, especially the Mediterranean region; it has also spread to other areas like the Americas. In some more areas where light-colored eyes are relatively rare, people with blue eyes are feared to possess the power to bestow the curse, intentionally or unintentionally. Belief in the evil eye features in Islamic mythology; it is not a part of Islamic doctrine, however, and is more a feature of Islamic folk religion. The evil eye is also significant in Jewish folklore; i ...

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Evil eye, Evil eye - Distribution of the belief, Evil eye - Talismans offering protection, Evil eye - Modern usage

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Attempts to ward off the curse of the evil eye resulted in a number of talismans being resorted to. Painted balls (or disks) painted with a blue circle with a concentric black circle inside representing an evil eye are common talismans in the Middle East. A blue eye can also be found on some forms of the Hand of Fatima (or Hamsa), an amulet against the evil eye in the Middle East. The large eyes often seen painted at the prows of Mediterranean boats are there, traditionally, to ward off the evil eye; the staring eyes return the malici ...

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Evil eye, Evil eye - Distribution of the belief, Evil eye - Talismans offering protection, Evil eye - Modern usage

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The gaze can be characterized by who is doing the looking: the spectator's gaze: the spectator who is viewing the text. This is often us, the audience of a certain text, intra-diegetic gaze, where one person depicted in the text who is looking at another person or object in the text, such as another character looking at another, extra-diegetic gaze, where the person depicted in the text looks at the spectator, such as an aside, or an acknowledgement of the fourth wall, or the camera's gaze, which is the gaze of the ...

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Gaze, Gaze - Forms of gaze, Gaze - Effects of gaze, Gaze - Gaze and feminist theory, Gaze - Responses to male gaze, Gaze - Gaze and psychology

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The relation of body language to animal communication has often been discussed. Human paralanguage may represent a continuation of forms of communication that our non-linguistic ancestors already used, or it may be that it has been changed by co-existing with language. Some species of animals are especially adept at detecting human body language, both voluntary and involuntary: this is the basis of the Clever Hans effect (a source of artifact in comparative psychology), and was also the reason for trying to teach the chimpanzee Washoe Americ ...

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Body language, Body language - Voluntary body language, Body language - Involuntary body language, Body language - Origins of body language, Body language - The importance of body language in groups, Body language - Examples

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Gazing and seeing someone gaze upon another provides us with a lot of information about our relationship to the subjects, or the relationships between the subjects upon whom we gaze, or the situation in which the subjects are doing the gazing. The mutuality of the gaze can reflect power structure, or the nature of a relationship between the subjects, as proposed by Catherine Lutz and Jane Collins, where this "tell[s] us who has the right and/or need to look at whom". Gazing can often reflect emotion without speech - in Western culture, continued staring upon another c ...

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Gaze, Gaze - Forms of gaze, Gaze - Effects of gaze, Gaze - Gaze and feminist theory, Gaze - Responses to male gaze, Gaze - Gaze and psychology

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When photographed with a flash, the iris only reacts to protect the retina, and not fast enough to avoid the red-eye effect. This represents reflection of light from the back of the eye, and is closely related to the term red reflex, used by ophthalmologists in describing appearances on fundal examination. When used as a descriptive term in medicine, the meaning of "red eye" is quite different, and indicates that the bulbar conjunctiva is reddened due to dilatation of superficial blood vessels. Leaving aside rarities, it ...

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Iris anatomy, Iris anatomy - General structure, Iris anatomy - Histological features, Iris anatomy - Anterior surface features, Iris anatomy - Posterior surface features, Iris anatomy - Embryology, Iris anatomy - Color, Iris anatomy - Genetic and physical factors determining iris color, Iris anatomy - Faking the iris color, Iris anatomy - Iris color as paternity test, Iris anatomy - Different colors in the two eyes, Iris anatomy - Red eye

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Contact lenses are available in a number of varieties. Contact lens - Corrective vs. cosmetic contact lenses. A corrective contact lens is a contact lens designed to improve vision, whereas a cosmetic contact lens is a contact lens designed to change the appearance of the eye. Sometimes the two overlap. Although many people wear contact lenses for functional reasons, they are frequently referred to as a cosmetic alternative to eyeglasses. Conversely, some peop ...

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Contact lens, Contact lens - History, Contact lens - Usage, Contact lens - Types of contact lenses, Contact lens - Corrective vs. cosmetic contact lenses, Contact lens - Rigid vs. soft contact lenses, Contact lens - Daily vs. extended wear contact lenses, Contact lens - Spherical vs. toric contact lenses, Contact lens - Cleaning and disinfection products, Contact lens - Parameters, Contact lens - Products

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The iris is usually strongly pigmented, with colors ranging from brown to green, blue, grey, and hazel. Occasionally its color is due to lack of pigmentation, as in the pinkish-white of oculo-cutaneous albinism, or to obscuration of its pigment by blood vessels, as in the red of an abnormally vascularised iris (although human albinos generally have very light blue eyes, as the unpigmented color of the human iris is a pale blue). Despite the wide range of colors, there is only one pigment that contributes substantially to normal human iris color, the dark pigment called melanin. Structurally, this huge molecule is only slightly different from ...

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Iris anatomy, Iris anatomy - General structure, Iris anatomy - Histological features, Iris anatomy - Anterior surface features, Iris anatomy - Posterior surface features, Iris anatomy - Embryology, Iris anatomy - Color, Iris anatomy - Genetic and physical factors determining iris color, Iris anatomy - Faking the iris color, Iris anatomy - Iris color as paternity test, Iris anatomy - Different colors in the two eyes, Iris anatomy - Red eye

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Showing one's palms to the listeners may mean openness and honesty, hiding the palms may mean deceit. Moving the hands close to the mouth or touching the nose may also indicate deceit. Pointing with a leg or knee towards another person may mean interest or acceptance of said person. Pointing your body away from the one you talk to means you would rather not be talking to the person and would rath ...

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Body language, Body language - Voluntary body language, Body language - Involuntary body language, Body language - Origins of body language, Body language - The importance of body language in groups, Body language - Examples

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The iris is divided into two major regions: The pupillary zone is the inner region whose edge forms the boundary of the pupil. The ciliary zone is the rest of the iris that extends to its origin at the ciliary body. The collarette is the region of the iris separating the pupillary portion from the ciliary portion. It is typically defined as the region where the sphincter muscle and dilator muscle overlap. See also:

Iris anatomy, Iris anatomy - General structure, Iris anatomy - Histological features, Iris anatomy - Anterior surface features, Iris anatomy - Posterior surface features, Iris anatomy - Embryology, Iris anatomy - Color, Iris anatomy - Genetic and physical factors determining iris color, Iris anatomy - Faking the iris color, Iris anatomy - Iris color as paternity test, Iris anatomy - Different colors in the two eyes, Iris anatomy - Red eye

Read more here: » Iris anatomy: Encyclopedia II - Iris anatomy - General structure