Spectacles were invented as an improvement of the "reading stones" of the high medieval period in Northern Italy in the second half of the 13th century. The medieval (11th or 12th century) rock crystal Visby lenses may or may not have been intended for use as burning glasses. These were primitive plano-convex lenses initially made by cutting a glass sphere in half. Between the 11th and 13th century " reading stones" were invented. The Arabic translation of Ptolemy's Optics became available in Latin translation in the 12th century ( Eugenius of Palermo 1154). The book was, however, received by medieval scholars in the Islamic world, and commented upon by Ibn Sahl (10th century), who was in turn improved upon by Alhazen ( Book of Optics, 11th century). Ptolemy (2nd century) wrote a book on Optics, which however survives only in the Latin translation of an incomplete and very poor Arabic translation. Both Pliny and Seneca the Younger (3 BC–65 AD) described the magnifying effect of a glass globe filled with water. Pliny also has the earliest known reference to the use of a corrective lens when he mentions that Nero was said to watch the gladiatorial games using an emerald (presumably concave to correct for nearsightedness, though the reference is vague). Pliny the Elder (1st century) confirms that burning-glasses were known in the Roman period. The oldest certain reference to the use of lenses is from Aristophanes' play The Clouds (424 BCE) mentioning a burning-glass. Others have suggested that certain Egyptian hieroglyphs depict "simple glass meniscal lenses". The so-called Nimrud lens is a rock crystal artifact dated to the 7th century BCE which may or may not have been used as a magnifying glass, or a burning glass. Some scholars argue that the archeological evidence indicates that there was widespread use of lenses in antiquity, spanning several millennia.
The lentil also gives its name to a geometric figure. The word lens comes from lēns, the Latin name of the lentil (a seed of a lentil plant), because a double-convex lens is lentil-shaped. Lens for LSST, a planned sky surveying telescope
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