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A prescription of −1.00 +0.25 × 180 describes a lens that has a horizontal power of −1.00 D and a vertical power of −0.75 D. Only ophthalmologists write prescriptions in + cylinder. An optometrist would write a prescription in - (minus) cylinder. All spectacle and contact lenses would be made in minus cylinder.
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 ).
Ballistic sunglasses or prescription eyeglasses must meet the same requirements. In brief, the U.S. military standard requires that ballistic eyewear must be able to withstand up to a 3.8 mm (.15 caliber) projectile at 195 m/s (640 ft/s)) for spectacles and 5.6 mm (.22 caliber) projectile at 168–171 m/s (550–560 ft/s) for goggles.
1/20/2011 Following the description in the Axis section, 'in the meridian specified by axis in the prescription, the power is equal to the value listed under "sphere". ', the example in the "Variations in prescription writing" section where Spherical=+2.0, Cylindrical=+1.0, Axis=180° would give a power of +2.00 diopters at the 180° meridian.
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The U.S. military standard (MIL-PRF-31013), requires (at a minimum) that ballistic eyewear can always withstand a 0.15 caliber, 5.8 grain, T37 shaped projectile at a velocity of 640 to 660 feet per second (approximately 3.8 mm 0.376 g at a velocity of 195 – 201 m/s). Goggles are required to stop a 17-grain fragment simulating projectile ...
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