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by convention, an axis of 90° is vertical, 0° or 180° are horizontal; if the cylinder power is positive, the lens is most convergent 90° from the axis; if the cylinder power is negative, the lens is most divergent 90° from the axis; if the cylinder power is zero, the lens is spherical and has the same power in every meridian
GI glasses are eyeglasses issued by the American military to its service members. Dysphemisms for them include the most common " birth control glasses " ( BCGs ) and other variants. At one time, they were officially designated as regulation prescription glasses ( RPGs ).
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.
Eyewear retail is a steadily growing business, driven by the rising global population, economic development, increased consumer purchasing power, and the global prevalence of ocular diseases. [48] The increased use of digital screens has led to an increase in vision impairment , cataracts , myopia , hypermetropia , eye irritation , dry eyes ...
Man with glasses. A woman with glasses. Glasses, also known as eyeglasses or 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 for support.
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Several key mistakes could throw off the accuracy of blood pressure readings for people who take them at home. The average "normal" blood pressure is 120/80, according to the American Heart ...
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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