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Depending on the eyeglasses, they serve many functions. [37] Reading glasses These are general over-the-counter glasses which can be worn for easier reading, especially for defective vision due to aging called presbyopia. Single vision prescription lenses They can correct only one form of defective vision, either far-sightedness or near ...
The gradient starts at the wearer's distance prescription at the top of the lens and reaches a maximum addition power, or the full reading addition, at the bottom of the lens. The length of the progressive power gradient on the lens surface depends on the design of the lens, with a final addition power between 0.75 and 3.50 dioptres .
Across the world, screening programs are important for identifying children who have a need for spectacles but either do not wear any or have the wrong prescription. [14] Often, children who are suspected of having amblyopia are too young to be able to verbally recognize letters on the Snellen chart, making the eye examination challenging. [13]
Presbyopia can be corrected using glasses, contact lenses, multifocal intraocular lenses, or LASIK (PresbyLASIK) surgery. [2] [7] [4] The most common treatment is glass correction using appropriate convex lens. Glasses prescribed to correct presbyopia may be simple reading glasses, bifocals, trifocals, or progressive lenses. [4]
In glasses with powers beyond ±4.00D, the vertex distance can affect the effective power of the glasses. [4] A shorter vertex distance can expand the field of view, but if the vertex distance is too small, the eyelashes will come into contact with the back of the lens, smudging the lens and causing annoyance for the wearer.
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