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Clear lens extraction, also known as refractive lensectomy, custom lens replacement or refractive lens exchange is a surgical procedure in which clear lens of the human eye is removed. Unlike cataract surgery , where the cloudy lens is removed to treat a cataract , clear lens extraction is done to surgically correct refractive errors such as ...
Prentice's rule, named so after the optician Charles F. Prentice, is a formula used to determine the amount of induced prism in a lens: [3] = where: P is the amount of prism correction (in prism dioptres) c is decentration (the distance between the pupil centre and the lens's optical centre, in millimetres)
Any of the above features, color, polarization, gradation, mirroring, and materials, can be combined into the lens for a pair of sunglasses. Gradient glasses are darker at the top of the lens where the sky is viewed and transparent at the bottom. Corrective lenses or glasses can be manufactured with either tinting or darkened to serve as ...
improved lens manufacturing and measurement technology. Today the complex surfaces of a progressive lens can be cut and polished on computer-controlled machines, allowing 'freeform surfacing', as opposed to the earlier casting process, thus explaining the difference in price.
But the glasses themselves (which took around 10 days to arrive — your mileage may vary) are great; they're lightweight and comfortable, and Pair nailed my fairly complicated progressive-lens ...
This specifies the part of the prescription designed primarily to improve far vision. In a bifocal lens, this generally indicates what is to be placed in the top segment. NV is an abbreviation for near vision. This may represent a single-vision lens prescription to improve near work, or the reading portion of a bifocal lens.
Welding glass protects against glare and flying sparks. It is a more extreme implementation of the same idea as sunglasses, suited to the more intense light generated during welding. Arc welding goggles must be much darker than blowtorch goggles. Shades 12, 13, and 14 welding glass must be used to stare directly at the sun or a solar eclipse.
A corrective lens is a transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye.