Eyes, vitamin

Retinol (RET-uh-nol) is the scientific name for vitamin A, a vitamin found only in animals. It occurs as a yellowish to orange powder with a slight brownish cast and is a relatively stable compound. Retinol is converted in the body from an alcohol to the corresponding aldehyde, retinal (C2oH280), one of the primary chemical compounds involved in the process by which light is converted to nerve impulses in the retina of the eye. Vitamin A is also required for a number of other biochemical reactions in the body, including growth and development of tissue and maintenance of the immune system. 

In the retinal cells of the eye, vitamin A (all-trans-retinol) is converted into the 11-ds-isomer, which is then oxidised to 11-cts-retinaldehde. In the dark the latter then combines with the protein opsin to form rhodopsin (visual purple), which is the photoreceptor for vision at low light intensities. When light falls on the retina, the czs-retinaldehyde molecule is converted back into the aW-trans form and is released from the opsin. This conversion results in the transmission of an impulse up the optic nerve. The all-frans-retinaldehyde is converted to all-trans-retinol, which re-enters the cycle, thus continually renewing the light sensitivity of the retina (Rg. 5.2). 

In the eye, vitamin A fluorescence was obtained from the rod and cone layer of the retina, very intense in the light-adapted eye and less intense in the dark-adapted eye. This is in keeping with the view that the protein-vitamin complex, retinene, which is formed from rhodopsin under the influence of light, liberates vitamin A, which subsequently becomes resynthesized into rhodopsin. 

The sohd product and its aqueous solutions are mildly acidic and irritate the skin, eyes, and mucous membranes. The soHd material when moist generates the pungent, irritating odor of sulfur dioxide. Food-grade sodium metabisulfite is permitted ia those foods that are not recognized as sources of vitamin B, with which sulfur dioxide reacts (316) (see Vitamins,THIAMINE). 

The stmcture of vitamin A [11103-57-4] and some of the important derivatives are shown in Figure 1. The parent stmcture is aH-Zra/ j -retinol [68-26-8] and its lUPAC name is (all-E)-3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexen-l-yl)-2,4,6,8-nonatetraen-l-ol (1). The numbering system for vitamin A derivatives parallels the system used for the carotenoids. In older Hterature, vitamin A compounds are named as derivatives of trimethyl cyclohexene and the side chain is named as a substituent. For retinoic acid derivatives, the carboxyl group is denoted as C-1 and the trimethyl cyclohexane ring as a substituent on C-9. The stmctures of vitamin A and -carotene were elucidated by Karrer in 1930 and several derivatives of the vitamin were prepared by this group (5,6). In 1935, Wald isolated a substance found in the visual pigments of the eye and was able to show that this material was identical with Karrer s retinaldehyde [116-31-4] (5) (7). 

Solutions in contact with polyvinyl chloride can become contaminated with trace amounts of lead, titanium, tin, zinc, iron, magnesium or cadmium from additives used in the manufacture and moulding of PVC. V-Phenyl-2-naphthylamine is a contaminant of solvents and biological materials that have been in contact with black rubber or neoprene (in which it is used as an antioxidant). Although it was only an artefact of the separation procedure it has been isolated as an apparent component of vitamin K preparations, extracts of plant lipids, algae, livers, butter, eye tissue and kidney tissue [Brown Chem Br 3 524 1967]. 

The treatment of an autoimmune disease very much depends on the nature of the clinical outcome it causes. Although the formation of autoantibodies causes the inactivation of the gastric intrinsic factor, the subsequent shortage of vitamin B12 can be easily overcome by supplying it via an parenteral route. Lifelong immunosuppression (with all its side effects) thus is inappropriate. When, however, as in sympathetic ophtalmia, after damage of the first eye the second eye is endangered, an even drastic immunosuppression is mandatory. 

Ascorbic acid is photosensitive and unstable in aqueous solution at room temperature. During storage of foods, vitamin C is inactivated by oxygen. This process is accelerated by heat and the presence of catalysts. Ascorbic acid concentration in human organs is highest in adrenal and pituitary glands, eye lens, liver, spleen, and brain. Potatoes, citrus fruits, blade currants, sea buckthorns, acerola, rose hips, and red paprika peppers are among the most valuable vitamin C sources [1,2]. 

The bright colors of flowers and the varied hues of autumn leaves have always been a cause for delight, but it was nor until the twentieth century that chemists understood how these colors arise from the presence of organic compounds with common structural features. They discovered how small differences in the structures of the molecules of these compounds can enhance photosynthesis, produce important vitamins, and attract pollinating bees. They now know how the shapes of molecules and the orbitals occupied by their electrons explain the properties of these compounds and even the processes taking place in our eyes that allow us to see them. 

Health benefits — Research reports indicate that natural (3-carotene possesses numerous benefits for the human body and consistently supports the use of (3-carotene as part of the human diet. The human body converts (3-carotene to vitamin A via body tissues as opposed to the liver, hence avoiding a build-up of toxins in the liver. Vitamin A is essential for the human body in that it assists the immune system and helps battle eye diseases such as cataracts and night blindness, various skin ailments such as acne, signs of aging, and various forms of cancer. 

Tripathi, B. and Tripathi, R. (1984). Cellular and subcellular events in retinopathy of oxygen toxicity with a preliminary report on the preventative role of vitamin E and gamma-aminobutyric acid a study in vitro. Curr. Eye Res. 3, 193-208. 

There are no approved pharmacologic treatments for atrophic AMD. The Age-Related Eye Disease Study showed that a supplement containing ascorbic acid 500 mg, vitamin E 400 IU, beta carotene 15 mg, zinc oxide 80 mg, and cupric oxide 2 mg reduced the rate of clinical progression of all types of AMD by 28% in patients with at least intermediate macular degeneration. No benefit was seen in patients with earlier stages of age-related maculopathy however, the duration of the study may have been insufficient to detect this benefit.25... 

Age-Related Eye Disease Study Research Group (2007), The relationship of dietary carotenoid and vitamin A, E, and C intake with age-related macular degeneration in a case-control study, AREDS Report No. 22, Arch. Ophthalmol. 125 1225-1232. 

Seddon, J. M., U. A. Ajani et al. (1994). Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. Eye disease case-control study group. JAMA 272(18) 1413-1420. 

We have mentioned microwave ovens a few times already. Although we might employ such an oven regularly, no one has actually seen microwave radiation. The photons are wholly invisible. The phenomenon of sight can be simplified to the photo-effected transformation of a pigment related to retinal within the retina at the back of the eye. Retinal is derived from vitamin A. 

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