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Peripheral Light Focusing
Peripheral Light Focusing (PLF) can be described as the focusing of Solar Ultraviolet Radiation (SUVR) at the nasal limbus of the cornea. SUVR incident at the temporal limbus passes across the corneal dome and focuses at the nasal limbus. The limbal region is a stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can change into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell ... rich tissue. Ocular conditions such as pinguecula and pterygium may occur due to the result of this increased exposure to SUVR in limal area, but it is not the only cause of pterygium formation. References Eye {{eye-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ultraviolet
Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs, Cherenkov radiation, and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. The photons of ultraviolet have greater energy than those of visible light, from about 3.1 to 12 electron volts, around the minimum energy required to ionize atoms. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack sufficient energy, it can induce chemical reactions and cause many substances to glow or fluoresce. Many practical applications, including chemical and biological effects, are derived from the way that UV radiation can interact with organic molecules. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corneal Limbus
The corneal limbus (''Latin'': corneal border) is a highly vascularized and pigmented zone between the cornea, conjunctiva, and the sclera (the white of the eye) that protects and heals the cornea. The cornea is composed of three primary cell types: epithelial cells, corneal fibroblasts, and endothelial cells. The corneal surface is one of the body's most specialized structures that undergoes continuous cellular renewal and regeneration. It contains limbal epithelial stem cells (LESCs) in the palisades of Vogt. Limbal stem cell deficiency (LSCD) can lead to disorders where limbal stem cells are damaged or absent. Additional disorders involving the corneal limbus are caused by deficiencies in interactions between ocular structures, developmental anomalies, and cancer. This article explores the structure, functions, disorders, and clinical significance of the corneal limbus. Etymology The word "limbus" comes from the Latin meaning "border." Structure The corneal limbus is th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cornea
The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea Refraction, refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. The cornea can be reshaped by surgical procedures such as LASIK. While the cornea contributes most of the eye's focusing power, its Focus (optics), focus is fixed. Accommodation (eye), Accommodation (the refocusing of light to better view near objects) is accomplished by changing the geometry of the lens. Medical terms related to the cornea often start with the prefix "''wikt:kerat-, kerat-''" from the Ancient Greek, Greek word κέρας, ''horn''. Structure The cornea has myelinated, unmyelinated nerve endings sensitive to touch, temperature and chemicals; a to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stem Cell
In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can change into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell in a cell lineage. They are found in both embryonic and adult organisms, but they have slightly different properties in each. They are usually distinguished from progenitor cells, which cannot divide indefinitely, and precursor or blast cells, which are usually committed to differentiating into one cell type. In mammals, roughly 50 to 150 cells make up the inner cell mass during the blastocyst stage of embryonic development, around days 5–14. These have stem-cell capability. '' In vivo'', they eventually differentiate into all of the body's cell types (making them pluripotent). This process starts with the differentiation into the three germ layers – the ectoderm, mesoderm and endoderm – at the gastrulation stage. However, whe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pinguecula
A pinguecula is a common type of conjunctival stromal degeneration in the eye. It appears as an elevated yellow-white plaque in the bulbar conjunctiva near the limbus. Calcification may also be seen occasionally. Etiology The exact etiology is unknown, but it may be associated with aging and excessive exposure to UV light. Signs and symptoms It is seen as a yellow-white deposit on the conjunctiva adjacent to the limbus (the junction between the cornea and sclera). (It is to be distinguished clinically from a pterygium, which is a wedge shaped area of fibrosis that may grow onto the cornea.) A pinguecula usually does not cause any symptoms. It is most common in tropical climates and there is a direct correlation with UV exposure. Histologically, there is degeneration of the collagen fibers of the conjunctival stroma with thinning of the overlying epithelium and occasionally calcification. Actinic exposure of the thin conjunctival tissue is thought to cause fibroblasts to pro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pterygium (conjunctiva)
A pterygium of the eye (: ''pterygia'' or ''pterygiums'', also called surfer's eye) is a pinkish, roughly triangular tissue growth of the conjunctiva onto the cornea of the eye. It typically starts on the cornea near the nose. It may slowly grow but rarely grows so large that it covers the pupil and impairs vision. Often both eyes are involved. The cause is unclear. It appears to be partly related to long term exposure to UV light and dust. Genetic factors also appear to be involved. It is a benign growth. Other conditions that can look similar include a pinguecula, tumor, or Terrien's marginal corneal degeneration. Prevention may include wearing sunglasses and a hat if in an area with strong sunlight. Among those with the condition, an eye lubricant can help with symptoms. Surgical removal is typically only recommended if the ability to see is affected. Following surgery a pterygium may recur in around half of cases. The frequency of the condition varies from 1% to 33% in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
