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Perger prism. A Perger prism or Perger–Porro prism system is a prism, that is used to invert (rotate by 180°) an image. The special feature of this prism is that, like a traditional double Porro prism system, it manages this with only four beam deflections and has neither a roof edge with the accompanying phase correction problems, a ...
A refractometer is a laboratory or field device for the measurement of an index of refraction ( refractometry ). The index of refraction is calculated from the observed refraction angle using Snell's law. For mixtures, the index of refraction then allows the concentration to be determined using mixing rules such as the Gladstone–Dale relation ...
Vertex distance is important when converting between contact lens and glasses prescriptions and becomes significant if the glasses prescription is beyond ±4.00 diopters (often abbreviated D). The formula for vertex correction is , where F c is the power corrected for vertex distance, F is the original lens power, and x is the change in vertex distance in meters.
During prism adaptation, an individual wears special prismatic goggles that are made of prism wedges that displace the visual field laterally or vertically. In most cases the visual field is shifted laterally either in the rightward or leftward direction. While wearing the goggles, the individual engages in a perceptual motor task such as pointing to a visual target directly in front of them ...
Ophthalmic trial frame. ophthalmic trial frame is used to hold lenses and other accessories during correction of refractive errors. A trial frame is a tool used by ophthalmic professionals like ophthalmologists and optometrists. It is basically an adjustable spectacle frame with multiple cells, used to hold corrective lenses, and other ...
Camera lucida in use. A camera lucida is an optical device used as a drawing aid by artists and microscopists . The camera lucida projects an optical superimposition of the subject being viewed, onto the surface upon which the artist is drawing. The artist sees both scene and drawing surface simultaneously, as in a photographic double exposure.