Collins English Dictionary Irides is a definition of irides by The Free DictionaryIris.
The amount of light reaching the retina is controlled by the iris, a thin structure in the eye.The eye color is determined by the iris.The iris is the focal point of the eye.
The iris has two layers: a stroma and a pigmented epithelial cells.
The stroma is connected to two muscles, one of which contracts the pupil in a circular motion and the other which pulls the iris in folds.
The circle-radius dilator muscle is the opposing muscle of the sphinching muscle.When it's dilating, the iris inner smaller circle-circumference changes in size.The larger circle-circumference does not change the size.There is a constriction on the iris.
The back surface is covered by a layer that is two cells thick, but the front surface has no epithelium.The dilator muscles are projected on the anterior surface.Light can't pass through the iris to the retina because of the high pigment content.The sclera and the anterior ciliary body are attached to the root of the iris.The anterior uvea is the iris and ciliary body.The trabecular meshwork, located just in front of the iris root, is where the water in the eye drain out, which can lead to problems with vision and intraocular pressure.The iris along with the anterior ciliary body are used to drain humour from the eye.
The ciliary portion of the iris is separated from the pupils by the collarette.There is a vestige of the embryo in the collarette.The region where the sphincter muscle and dilator muscle overlap is typically defined.The iris is supplied with blood vessels by the radial ridges.The most peripheral part of the iris is the root.
The muscle cells of the iris are smooth in mammals and lizards, but striated in birds.The fish's irides are unable to dilate and contract because they don't have either.
The stroma and the anterior border layer of the iris are derived from the neural crest.
The color of the iris varies between brown, hazel, green, gray, and blue.Occasionally, the color of the iris is due to a lack of pigmentation, as in the pale-white of oculocutaneous albinism, or to obscuration of its pigment by blood vessels.The dark pigment melanin contributes the most to normal human iris color, despite the wide range of colors.One factor in determining the eye color of a person is the amount of melanin in the iris.This molecule is slightly different from the one found in skin and hair.There are variable amounts of eumelanin and pheomelanin produced by melanocytes.More of the former is found in brown-eyed people.
A person's epigenetic constitution is made up of the effects of texture, pigmentation, fibrous tissue, and blood vessels within the iris stroma.A person's "eye color" is the color of their iris, the transparent part of the eye, and the white sclera outside the area of interest.
The stromal pigment cells are brown to dark brown in color, while the iris pigment epithelium is black.Most human irises show a condensation of the brownish stromal melanin in the thin border layer, which by its anterior position has an overt influence on the overall color.The degree of dispersion of the melanin, which is in subcellular bundles, has some influence on the observed color, but melanosomes in the iris of humans and other vertebrates are not mobile.Alterations in iris color can be caused by abnormal clumping of melanosomes.The other stromal components reflect and absorb colors other than brown or black.There is a yellow "wear and tear" pigment that can enter into the visible eye color.
Many incorrect statements exist in the literature about the optical mechanisms by which the nonpigmented stromal components influence eye color.The most important element is the absorption and reflection by the biological molecule in the blood vessels.Tyndall scattering occurs in the sky as well.The interference phenomena in the feathers of birds do not contribute to the color of the human eye, but they are important in many animals.In-bearing cells and quasicrystalline formations enhance the optical effects and can be associated with interference effects.The chemical components remain the same, but the dependence of color on the angle of view is what distinguishes interference.White babies are usually blue-eyed due to scattering and absorption from the stroma.If brown or black color is seen, it's because of the amount of melanin deposited.
Eye color and its variations are not fully understood.In other species, the iris color can follow a different pattern.
Humans have very few amber-colored eyes.They have a solid orange/gold color that may have lighter shades of the same color within the iris.When the yellow pheomelanin is dominant within the iris, this is an unusual occurrence.Pheomelanin is found on individuals with green eyes.Green eyes have a strong presence of both pheomelanin and melanin.One may mistake amber eyes for brown in poor lighting.This can happen in pictures with poor lighting as well.It's easy to tell the difference between the two colors in natural areas.It's a common mistake to refer to amber eyes as hazel.Although similar, hazel eyes have a stronger presence of melanin with two very distinct colors within the iris, and often contain many speckles of mixed colors.
Heterochromia is an eye condition in which one iris is a different color from the other and the rest is the same color.Uncommon in humans, it is an indicator of ocular disease, such as chronic iritis or diffuse iris melanoma, but may also occur as a normal variant.It's less common to see sectors or patches of different colors in the same iris.Since his right iris had a darker color than his left, he was dubbed dikoros.
Heterochromia and variegated iris patterns are common in veterinary practice.The genetically determined Waardenburg syndrome of humans may be similar to the Heterochromia shown by the Siberia husky dogs.Heterochromia can be seen in some white cat fancies, with the most common pattern being one uniformly blue, the other copper, orange, yellow, or green.Some animals and some species have striking variation within the same iris.Several herding breeds, particularly those with a blue merle coat color, may show well-defined blue areas within a brown iris, as well as separate blue and darker eyes.Some horses that are part of the white, spotted, palomino, or cremello groups of breeds may show amber, brown, white and blue all within the same eye, without any sign of eye disease.There is a citation needed.
Proponents of iridodiagnosis believe that patterns, colors, and other characteristics of the iris can be examined to determine information about a patient's systemic health.The iris charts are used to divide the iris into zones for specific parts of the human body.The eyes are seen as "windows" into the body's state of health.10