Vitamin C is a water-soluble nutrient essential for life, used by the human body for many purposes. It is one of a number of such key nutrients called vitamins.
To the best of scientific knowledge, all animals and plants synthesize their own vitamin C, except for humans and a small number of other animals, including, apes, guinea pigs, the red-vented bulbul, a fruit-eating bat and a species of trout. This has led a minority of scientists, most notably Linus Pauling to conclude that failure to produce the chemical by an animal s ...
Vitreous humour is the clear aqueous solution that fills the space between the lens and the retina of the vertebrate eyeball. The solution is 99% water, but has a gelatinous viscosity two to four times that of water. The remaining solutes include salts, sugars, phagocytes, and a network of collagen fibres. The phagocytic cells are present to remove unwanted debris in the visual field. The primary purpose of the vitreous humour is to provide a cushioned support for the rest of the eye, as well as a clea ...
Visual processing in the brain goes through a series of processing stages. Destruction of the first visual cortical area, primary visual cortex (or V1 or striate cortex) leads to blindness in the part of the visual field that corresponds to the damaged cortical representation. The area of blindness - known as a scotoma - is in the visual field opposite the damaged hemisphere and can vary from a small area up to the entire hemifield.
Although individuals with damage to V1 are not consciously aware of stimuli presented in their blind fi ...
Retinol, the dietary form of vitamin A, is a fat-soluble, antioxidant vitamin important in vision and bone growth. It belongs to the family of chemical compounds known as retinoids. Retinol is ingested in a precursor form; animal sources (milk and eggs) contain retinyl esters, whereas plants (carrots, spinach) contain carotenoids. Tissue cells convert these precursors to retinol, and then to either retinal or retinoic acid.
Retinol - Chemical structure and function.
Many different geometric isomers o ...
Visual phototransduction is a process by which light is converted into electrical signals in the rod cells and cone cells of the retina of the eye. It is divided into an activation process and an inactivation process.
Other related archivescone cells, electrical signals, eye, light, retina, rod cells
The visual system is the part of the nervous system which allows organisms to see. It interprets the information from visible light to build a representation of the world surrounding the body. Note that different species are be able to see different part of the light spectrum; for example, some can see into the ultraviolet, while others can see into the infrared.
This article mostly describes the visual system of mammals, although other "higher" animals have similar visual systems. In this case, the visual system consists of:Including:
The ciliary body is the part of the eye containing the ciliary muscle and ciliary processes. There are two sets of ciliary muscles in the eye. They are near the front of the eye, above and below the lens. They are attached to the lens by connective tissue called zonular fibers, and are responsible for shaping the lens to focus light on the retina.
When the ciliary muscle relaxes, it flattens the lens which generally improves the focus for farther objects. When it contracts, the lens becomes more convex which generally i ...
The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye lying between the retina and the sclera. The choroid provides oxygen and nourishment to the outer layers of the retina [1].
Along with the ciliary body and iris, the choroid forms the uveal tract. In humans and other primates, darkly colored melanin pigment in the choroid helps limit reflections within the eye that would potentially result in the perception of confusing images. Poor vision frequently results from lack of thi ...
The term symptom (from the Greek syn = con/plus and pipto = fall, together meaning co-exist) has two similar meanings in the context of physical and mental health:
A symptom may loosely be said to be a physical condition which shows that one has a particular illness or disorder (see e.g. Longman, 1995). An example of a symptom in this sense of the word would be a rash. However, correctly speaking, this is known as a sign, as would any indication detectable by a person other than the sufferer in the ab ...
Color digital images are made of pixels, and pixels are made of combinations of primary colors. A channel in this context is the grayscale image of the same size as a color image, made of just one of these primary colors. For instance, an image from a standard digital camera will have a red, green and blue channel. A grayscale image has just one channel.
In the digital realm, there can be any number of conventional primary colors making up an image; a channel in this case is extended to be the grayscale image based on any such conventional primary color. By extension, a channel is any grayscale image ...
The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments" (J. Smythies [1]), while field of view "refers to the physical objects and light sources in the external world that impinge the retina". In other words, field of view is everything that (at a given time) causes light to fall onto the retina. This input is processed by the visual sys ...
Image:PDE5 1.jpg cGMP specific phosphodiesterase type 5 is an enzyme (EC 3.1.4.17) from the phosphodiesterase class. It is found in various tissues, most prominently the corpus cavernosum and the retina.
The phosphodiesterase (PDE) isozymes found in rod and cone photoreceptor cells of the retina belong to a large family of cyclic nucleotide PDEs that catalyze cAMP and cGMP hydrolysis.
The i ...
Zeaxanthin is one of the two carotenoids contained within the retina.
Within the central macula, zeaxanthin is the dominant component, whereas in the peripheral retina, lutein predominates.
Lutein and zeaxanthin have identical chemical formulas and are isomers, but they are not stereoisomers. The main difference between them is in the location of a double bond in one of the end rings. This difference gives lutein ...
Canthaxanthin is a food additive used for farmed salmon raised in environments where astaxanthin sources are not available. Canthaxanthin gives salmon a pink color similar to pink/red species of wild salmon, while at the same time acting as an antibiotic. It has E number E161g.
Health concerns have raised the issue of safety concerning the usage of canthaxanthin in commercially sold salmon. As a result, in the United States, food packaging must indicate if artificial coloring (including, but not limted to canthaxanthin) is added to the fish. In addition, the European Union has set limits on how mu ...
In the arts of painting, web design, and photography, color theory is a set of basic rules for mixing color to achieve a desired result. As pigment and light are different in terms of how they combine to create colors, so too are the rules for dealing with each. White light is composed of the mixture of the three primary hues red, green and blue. Black is approximated in pigment by mixing the primaries cyan, magenta and yellow (the imperfect primaries blue, red and yellow are the more traditional primaries due their colorfast properti ...
The watchmaker analogy is often used as a teleological argument (argument from design) in support of the view that the universe (or features of it) are the product of a conscious designer or designers.
Watchmaker analogy - History.
Monotheists have suggested: if we find a watch in a field, it is too complex to have appeared there by natural process so they assume that there must be a watchmaker responsible for its creation. Similarly, the argument goes, life is extremely complex and requires a creato ...
VIP is a peptide hormone containing 28 amino acid residues.
Its role in the intestine is to greatly stimulate secretion of water and electrolytes, as well as dilating intestinal smooth muscle, dilating peripheral blood vessels, and inhibiting gastrin-stimulated gastric acid secretion.
It is also found in the brain and some autonomic nerves. One region of the brain includes a specific region of the suprachiasmatic nuclei (SCN), which is the location of the 'master pacemaker'. Given that the SCN is responsible for detecting ambie ...
The lens or crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to focus on the retina.
In humans, the refractive power of the lens in its natural environment is approximately 15 dioptres, roughly one-fourth of the eye's total power.
The lens is flexible and its curvature is controlled by ciliary muscles. By changing the curvature of the lens, one can focus the eye on objects at different dis ...
Usher syndrome is a genetic disease causing deaf-blindness. It is essentially progressive retinitis pigmentosa combined with congenital hearing impairment. It is almost always inherited in an autosomal recessive pattern and is estimated to occur in 1 in 10,000 people. Whilst this is a rare genetic condition, it represents the major cause of syndromic deafness with blindness. The condition gets its name from British ophthalmologist, C.H. Usher, who in 1914 wrote a paper describing several cases in which the link between conge ...
