Spectacles sport variety of lens materials

June 15, 2011

These are exciting times to sell eyewear options to your patients.

These are exciting times to sell eyewear options to your patients.

Your lens toolbox should include the basic lens options, with a variety of specialty lenses to recommend when you find your patients using their eyes for very specific needs.

Although every patient's lens prescription demands specialized treatment, there are basic lenses suitable for lower-powered prescriptions. These patients will be happy with the most common lens materials: CR-39, crown glass, Trivex, and polycarbonate.

CR-39

This common lens material has the lowest index of refraction, which means that it will be the thickest lens material choice. While the thickness is negligible for low-powered lenses, it should be taken seriously with high-powered prescriptions.

With a specific gravity of 1.32 g/cm3 , it is average in weight. Where CR-39 shines is with an Abbe value of 58. The higher the Abbe value, the less chromatic aberration will occur when light is passing through the lens. CR-39 has an attractive price point and it is tinted easily.

Another important item to remember with CR-39 is that it does not protect much against UV rays. To make it UV-protective, it can be dipped in a special bath.

Although CR-39 is tough, it is not unbreakable. CR-39 has been a popular lens material, yet polycarbonate and Trivex are moving to the head of the class in lens materials.

Crown glass

Once our only lens material option, crown glass has become a "has-been" in the optical world. Although it is the most scratch-resistant lens material, breakage is an important consideration. With an index of refraction of 1.523, it is average in lens thickness. Glass is the heaviest lens material, with 1 cm3 of glass weighing 2.54 g. Glass has a chromatic aberration of 59, making it the least chromatic of all lens materials.

Additionally, glass does not provide any UV protection. This lens material obviously is not a choice for anyone who wears eyewear outdoors frequently, or when lens breakage is a concern.