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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)
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 ...
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.
Uncoated glasses lens (top) versus lens with anti-reflective coating. The reflection from the coated lens is tinted because the coating works better at some wavelengths than others. An antireflective , antiglare or anti-reflection ( AR ) coating is a type of optical coating applied to the surface of lenses , other optical elements, and ...
By shifting corrective lenses off axis, images seen through them can be displaced in the same way that a prism displaces images. Eye care professionals use prisms, as well as lenses off axis, to treat various orthoptics problems: Diplopia (double vision) Positive and negative fusion problems [ambiguous] [citation needed]
That feels exorbitant; they're just flimsy pieces of plastic, after all, easily lost or broken. They should be $10 apiece, maybe three for $20. Still, there's no denying the appeal of glasses that ...
The eye relief given in product specifications does not always give a realistic view of what a user can expect. Although eye-cups can usually be folded down to allow the spectacle wearer to get closer to binocular eyepieces, there are sometimes lens mountings that do not allow the theoretical eye relief to be obtained.
Adjustable focus lenses, like single-focus lenses, also reduce image-jump and spatial distortion in the field of view associated with traditional multi-focal lenses. Additionally, the ideal near-vision correction can be achieved with precision, because the variable lenses emulate the focusing action of the youthful (non-presbyopic) eye.
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