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Adjustable focus eyeglasses are eyeglasses with an adjustable focal length. They compensate for refractive errors (such as presbyopia) by providing variable focusing, allowing users to adjust them for desired distance or prescription, or both.
In transport, driver visibility is the maximum distance at which the driver of a vehicle can see and identify prominent objects around the vehicle. Visibility is primarily determined by weather conditions (see visibility) and by a vehicle's design.
Progressive lenses (those that function as both reading and distance glasses) start at $295, while tinted prescription lenses cost an additional $100 from the base model.
A corrective lens is a transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye.
Glasses, also known as eyeglasses and 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.
In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres. At this distance, the symbols on the line representing "normal" acuity subtend an angle of five minutes of arc, and the thickness of the lines and of the spaces between the lines subtends one minute of arc.
Example of a situation where glare can be problematic, if, for instance, the ability to determine the distance and speed of passing cars is reduced. Glare can reduce visibility by: Reduction of brightness of the rest of the scene by constriction of the pupils
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While pinhole glasses are claimed to be useful for people who are both near- and far-sighted, they are not recommended [citation needed] for people with over 6 diopters of myopia. Additionally, pinhole glasses reduce brightness and peripheral vision, and thus should not be used for driving or when operating machinery.
Vertex distance is the distance between the back surface of a corrective lens, i.e. glasses (spectacles) or contact lenses, and the front of the cornea.