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Glasses, also known as eyeglasses and spectacles, are vision eyewear with clear or tinted lenses mounted in a frame that holds them in front of a person's eyes, typically utilizing a bridge over the nose and hinged arms, known as temples or temple pieces, that rest over the ears. Man with glasses. Glasses are typically used for vision ...
An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient. If an eye examination indicates that corrective lenses are appropriate, the prescriber generally ...
Optics and vision. Vision of humans and other organisms depends on several organs such as the lens of the eye, and any vision correcting devices, which use optics to focus the image. The eyes of many animals contains a lens that focuses the light of its surroundings onto the retina of the eye. This lens is essential to producing clear images ...
Astigmatism (optical systems) An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- (a ...
Adjustable focus eyeglasses are eyeglasses with an adjustable focal length. They compensate for refractive errors (such as presbyopia) by providing variable focusing, allowing users to adjust them for desired distance or prescription, or both. Current bifocals and progressive lenses are static, in that the user has to change their eye position ...
A photochromic eyeglass lens, part of the lens darkened after exposure to sunlight while the other part remained covered. A photochromic lens is an optical lens that darkens on exposure to light of sufficiently high frequency, most commonly ultraviolet (UV) radiation. In the absence of activating light, the lenses return to their clear state.
A photochromic eyeglass lens, after exposure to sunlight while part of the lens remained covered by paper. Photochromism is the reversible change of color upon exposure to light. It is a transformation of a chemical species (photoswitch) between two forms by the absorption of electromagnetic radiation (photoisomerization), where the two forms ...
Eyepiece. A collection of different types of eyepieces. An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is named because it is usually the lens that is closest to the eye when someone looks through an optical device to observe an object or sample.
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