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 ...

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 - Acuity

See also:

Visual acuity, Visual acuity - History, Visual acuity - Physiology of visual acuity, Visual acuity - Visual acuity expression, Visual acuity - Measurement, Visual acuity - Measurement considerations, Visual acuity - Normal vision

Read more here: » Visual acuity: Encyclopedia II - Visual acuity - Physiology of visual acuity

Visual acuity depends upon how accurately light is focused on the retina (mostly the macular region), the integrity of the eye's neural elements, and the interpretative faculty of the brain [1]. "Normal" visual acuity is frequently considered to be what was defined by Snellen as the ability to recognize an optotype when it subtended 5 minutes of arc, that is Snellen's chart 20/20 feet, 6/6 meter, 1.00 decimal or 0.0 logMAR. In humans, the maximum acuity ...

See also:

Visual acuity, Visual acuity - History, Visual acuity - Physiology of visual acuity, Visual acuity - Visual acuity expression, Visual acuity - Measurement, Visual acuity - Measurement considerations, Visual acuity - Normal vision

Read more here: » Visual acuity: Encyclopedia II - Visual acuity - Normal vision

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

Read more here: » Eye: Encyclopedia - Eye

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

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 ...

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 - Anatomy

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

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 ...

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 - Acuity

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 ...

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 - Evolution 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 ...

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 - Cytology

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 ...

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

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 ...

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 - Eye movement

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 - 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 - Eye

Visual acuity (VA) is one of many components of the visual perception sense and is defined as the eye's ability to resolve fine details. VA is a quantitative measure to see an in-focus image at a certain, standarized distance. VA is the most common measurement of visual function that is performed in a clinical setting. Visual acuity - History. In 1843 Kuechler, a German ophthalmologist, developed a set of three charts, but his work was almost completely forgotten. In 1854 Jaeger published a set of re ...

Including:

Visual acuity - History Visual acuity - Physiology of visual acuity Visual acuity - Visual acuity expression Visual acuity - Measurement Visual acuity - Measurement considerations Visual acuity - Normal vision

Read more here: » Visual acuity: Encyclopedia - Visual acuity

Visual acuity is typically measured monocularly rather than binocularly with the aid of an optotype chart for distant vision, an optotype chart for near vision, and an occluder to cover the eye not being tested. The examiner may also occlude an eye by sliding a tissue behind the patient's eyeglasses, or instructing the patient to use his or her hand. This latter method is typically avoided in professional settings as it may inadvertently allow the patient to peek through his or her fingers, or press the eye and alter the measurement when tha ...

See also:

Visual acuity, Visual acuity - History, Visual acuity - Physiology of visual acuity, Visual acuity - Visual acuity expression, Visual acuity - Measurement, Visual acuity - Measurement considerations, Visual acuity - Normal vision

Read more here: » Visual acuity: Encyclopedia II - Visual acuity - Measurement

Ideally, the eye examination consists of an external examination, followed by specific tests for visual acuity, pupil function, extraocular muscle motility, visual fields, intraocular pressure and ophthalmoscopy through a dilated pupil. A minimal eye examination consists of tests for visual acuity, pupil function, and extraocular muscle motility, as well as direct ophthalmoscopy through an undilated pupil. ...

See also:

Eye examination, Eye examination - Comprehensive eye examination, Eye examination - Case history, Eye examination - Entrance tests, Eye examination - Refraction, Eye examination - Functional tests, Eye examination - Health assessment, Eye examination - Setting, Eye examination - Basic examination, Eye examination - External examination, Eye examination - Visual acuity, Eye examination - Pupil function, Eye examination - Ocular motility, Eye examination - Visual field confrontation testing, Eye examination - Intraocular pressure, Eye examination - Ophthalmoscopy, Eye examination - Slit lamp

Read more here: » Eye examination: Encyclopedia II - Eye examination - Setting

Eye examination - Case history. Eye examination - Entrance tests. External examination Visual acuity Amplitude of accommodation Color vision Cover test Stereopsis Near point of convergence Extraocular motilities Pupils Visual field screening Interpupillary distance Eye examination - Refraction. Lensometry Keratometry Retinos ...

See also:

Eye examination, Eye examination - Comprehensive eye examination, Eye examination - Case history, Eye examination - Entrance tests, Eye examination - Refraction, Eye examination - Functional tests, Eye examination - Health assessment, Eye examination - Setting, Eye examination - Basic examination, Eye examination - External examination, Eye examination - Visual acuity, Eye examination - Pupil function, Eye examination - Ocular motility, Eye examination - Visual field confrontation testing, Eye examination - Intraocular pressure, Eye examination - Ophthalmoscopy, Eye examination - Slit lamp

Read more here: » Eye examination: Encyclopedia II - Eye examination - Comprehensive eye examination

Visual loss results in the absence of vision where it existed before, which can happen either acutely (i.e. abruptly) or chronically (i.e. over a long period of time). The effects of visual loss can, before the acquisition of alternative adaptations and skills, be devastating; especially when a person's vision disappears over a short period of time. Visual loss - Acute visual loss. Acute visual loss may be dramatic in presentation, and is almost always alarming to the person experiencing the loss. It ...

Including:

Visual loss - Acute visual loss
Visual loss - Media opacity Visual loss - Retinal disease Visual loss - Optic nerve disease Visual loss - Visual pathway disorder Visual loss - Functional disorder

Read more here: » Visual loss: Encyclopedia - Visual loss

Blindness can be defined physiologically as the condition of lacking visual perception. The definition as it applies to people thus legally classified is, however, more complex. "Blindness" also applies to partial visual impairment: In North America and most of Europe, legal blindness is defined as visual acuity (vision) of 20/200 (6/60) or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet from an object to see it with the same degree of cl ...

Including:

Blindness - Causes of blindness
Blindness - Diseases Blindness - Abnormalities and injuries Blindness - Genetic defects
Blindness - Adaptive techniques Blindness - Tools
Blindness - Mobility Blindness - Reading and magnification Blindness - Computers Blindness - Other aids
Blindness - Social attitudes towards blindness

Read more here: » Blindness: Encyclopedia - Blindness

Eye examination - External examination. External examination of eyes consists of inspection of the eyelids, surrounding tissues and palpebral fissure. Palpation of the orbital rim may also be desirable, depending on the presenting signs and symptoms. The conjunctiva and sclera can be inspected by having the individual look up, and shining a light while retracting the upper or lower eyelid. The cornea and iris may be similarly inspected. < ...

See also:

Eye examination, Eye examination - Comprehensive eye examination, Eye examination - Case history, Eye examination - Entrance tests, Eye examination - Refraction, Eye examination - Functional tests, Eye examination - Health assessment, Eye examination - Setting, Eye examination - Basic examination, Eye examination - External examination, Eye examination - Visual acuity, Eye examination - Pupil function, Eye examination - Ocular motility, Eye examination - Visual field confrontation testing, Eye examination - Intraocular pressure, Eye examination - Ophthalmoscopy, Eye examination - Slit lamp

Read more here: » Eye examination: Encyclopedia II - Eye examination - Basic examination