Achromatopsia: An hereditary disorder of sight due to a lack of cone vision - that type of vision provided by the cone photoreceptors in the retina. In the normal eye, there are some 6 million cone photoreceptors; they are located largely in the center of the retina. Lacking cones, persons with achromatopsia have to rely on their rod photoreceptors. There are about 100 million rod photoreceptors which are located mainly around the periphery of the retina. Rods saturate at higher levels of illumination and do not provide color vision or good detail vision.
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Blindness: Loss of useful sight. Blindness can be temporary or permanent. Damage to any portion of the eye, the optic nerve, or the area of the brain responsible for vision can lead to blindness. There are numerous (actually, innumerable) causes of blindness. The current politically correct terms for blindness include visually handicapped and visually challenged.
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Colorblindness: The inability to perceive colors in a normal fashion. The most common forms of colorblindness are inherited as sex-linked (X-linked) recessive traits. Females are carriers and males are affected. As a result, approximately 1 in 8 males is colorblind as compared to less than 1 in 100 females.
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Condition: The term "condition" has a number of biomedical meanings including the following: - An unhealthy state, such as in "this is a progressive condition."
- A state of fitness, such as "getting into condition."
- Something that is essential to the occurrence of something else; essentially a "precondition."
- As a verb: to cause a change in something so that a response that was previously associated with a certain stimulus becomes associated with another stimulus; to condition a person, as in behavioral conditioning.
Cone: A type of specialized light-sensitive cell (photoreceptor) in the retina of the eye that provide sharp central vision and color vision.
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Eye: The organ of sight. The eye has a number of components. These components include but are not limited to the cornea, iris, pupil, lens, retina, macula, optic nerve, choroid and vitreous.
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Genetic: Having to do with genes and genetic information.
Health: As officially defined by the World Health Organization, a state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity.
Lens: The transparent structure inside the eye that focuses light rays onto the retina (the nerve layer that lines the back of the eye, senses light and creates impulses that go through the optic nerve to the brain). The lens was named after the lentil bean because it resembled it in shape and size.
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Nerve: A bundle of fibers that uses chemical and electrical signals to transmit sensory and motor information from one body part to another. See: Nervous system.
Pigment: A substance that gives color to tissue. Pigments are responsible for the color of skin, eyes, and hair.
Red-green colorblindness: A form of colorblindness in which red and green are perceived as identical. This is the most common type of colorblindness. It is inherited in an X-linked recessive manner and affects 6% of males. It is also known as deutan colorblindness, deuteranopia, and Daltonism.
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Retina: The retina is the nerve layer that lines the back of the eye, senses light, and creates impulses that travel through the optic nerve to the brain. There is a small area, called the macula, in the retina that contains special light-sensitive cells. The macula allows us to see fine details clearly.
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Retinal: Pertaining to the retina , the extraordinary layer of neurons (nerve cells) that line the back of the eye, which can sense light and create impulses capable of voyaging through the optic nerve to the brain where the impulses are recognized as an image.
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Rod: A type of specialized light-sensitive cell (photoreceptor) in the retina of the eye that provides side vision and the ability to see objects in dim light (night vision).
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- Genetic Disease - Learn about genetic disease caused by abnormalities in an individual's genome. There are four types of genetic inheritance, single, multifactoral, chromosome abnormalities, and mitochondrial inheritance. Genetic testing is available for some genetic diseases.
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