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An eyeglass prescription. Similar to medical prescriptions, eyeglass prescriptions are written on paper pads or included in a patient's electronic health record, and contain a number of different abbreviations and terms: DV is an abbreviation for distance vision. This specifies the part of the prescription designed primarily to improve far vision.
A current mirror is a circuit designed to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. The current being "copied" can be, and sometimes is, a varying signal current.
Optical glass refers to a quality of glass suitable for the manufacture of optical systems such as optical lenses, prisms or mirrors.Unlike window glass or crystal, whose formula is adapted to the desired aesthetic effect, optical glass contains additives designed to modify certain optical or mechanical properties of the glass: refractive index, dispersion, transmittance, thermal expansion and ...
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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A Snellen chart or other eye chart may initially reveal reduced visual acuity. A keratometer may be used to measure the curvature of the steepest and flattest meridians in the cornea's front surface. [14] Corneal topography may also be used to obtain a more accurate representation of the cornea's shape. [15]
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In late 2017, Snapchat wrote off $40m worth of unsold Spectacles inventory and unused parts. As of May 2018, the company sold 220,000 pairs, which was less than initially expected. [ 14 ] In April 2018, the company launched Spectacles 2.0, which included additional colors, lighter frames, the option of mirrored lenses, and the removal of the ...