Eye - Eyelids

An eye is an organ that detects light. Different kinds of light-sensitive organs are found in a variety of creatures. The simplest eyes do nothing but detect whether the surroundings are light or dark. More complex eyes are used to provide the sense of vision. Many complex organisms including some mammals, birds, reptiles and fish have two eyes which may be placed on the same plane to be interpreted as a single three-dimensional "image" (binocular vision), as in humans; or on different planes producing two separate "images" (monocular ...

Including:

• 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

Read more here: » Eye: Encyclopedia II - Eye - Evolution of eyes

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

Read more here: » Eye: Encyclopedia II - Eye - Eye movement

Eye - The orbit. In many species, the eyes are inset in the portion of the skull known as the orbits or eyesockets. This placement of the eyes helps to protect them from injury. Eye - Eyebrows. In humans, the eyebrows redirect flowing substances (usually rainwater) away from the eye. Water in the eye can alter the refractive properties of the eye and blur vision. It can also wash away the tear fluid, and its beneficial effects, and can damage the cornea, due to osmotic differences between tear fluid and freshwa ...

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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 - Adnexa and related parts

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

Read more here: » Eye: Encyclopedia II - Eye - Acuity

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 ...

See also:

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 ...

See also:

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

Eye - The orbit. In many species, the eyes are inset in the portion of the skull known as the orbits or eyesockets. This placement of the eyes helps to protect them from injury. Eye - Eyebrows. In humans, the eyebrows redirect flowing substances (usually rainwater) away from the eye. Water in the eye can alter the refractive properties of the eye and blur vision. It can also wash away the tear fluid - along with it the protective lipid layer - and can alter corneal physiology, ...

See also:

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 - Adnexa and related parts

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

Read more here: » Eye: Encyclopedia II - Eye - Varieties of eyes

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

Read more here: » Eye: Encyclopedia II - Eye - Cytology

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

Read more here: » Eye: Encyclopedia II - Eye - Anatomy

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 ...

See also:

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

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 cepha ...

See also:

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 - Varieties of eyes