CR-39 (Columbia Resin) is also known as plastic or hard resin. Lens made of CR-39 are much lighter than glass. But CR-39 is less scratch resistant and must be coated to improve index: 1.498.Advantages of these lenses are :
Lighter than glasses, readily tintable, less like to fog, suitable for children and one eyed patients.
Monday, 20 February 2017
CR-39 lens
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Advantages: The chart is familiar Inexpensive, quick and easy to use and interpret Disadvantages: Snellen chart has only one 6/60 lette...
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Preferences: Similarly quantities of letters per line. Consistently separating amongst lines and letters. Uniform movement ...
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