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It has been proposed that glass eye covers in hieroglyphs from the Old Kingdom of Egypt (c. 2686–2181 BCE) were functional simple glass meniscus lenses. The so-called Nimrud lens, a rock crystal artifact dated to the 7th century BCE, might have been used as a magnifying glass, although it could have simply been a decoration.
The Peli Lens is a mobility aid for people with homonymous hemianopia. It is also known as “EP” or Expansion Prism concept and was developed by Dr. Eli Peli of Schepens Eye Research Institute in 1999. It expands the visual field by 20 degrees.
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.
The spectrometer uses a prism or a grating to spread the light into a spectrum. This allows astronomers to detect many of the chemical elements by their characteristic spectral lines. These lines are named for the elements which cause them, such as the hydrogen alpha, beta, and gamma lines.