Not your everyday go-to lens, 1.74 can be a real problem solver for extremely high prescriptions.
Mitsui Chemicals America and Miki USA supply the bulk of lens casters in our industry with monomer to cast 1.74 lenses. Here are five key points you may not know about this material.
1. The Abbe value of 1.74 material is about 32, comparable to polycarbonate. With over 50% of lenses sold today being polycarbonate, one might infer that this Abbe value has little effect on vision. However, it’s important to remember that 1.74 lenses are used for the highest prescriptions, and in those cases, the effects of a low Abbe value are more evident to the wearer.
2. With 80% of the monomer made from plant products, 1.74 can be considered an eco-friendly material. Being greener than other high-index lenses, it is also easier to surface and finish.
3. Like almost all high-index lens materials, 1.74 material absorbs nearly 100% of ultraviolet radiation.
4. Because 1.74 lenses do not inherently absorb blue light, it may be a good idea to have these lenses coated with a blue light attenuating treatment, especially with the continuing evidence that blue light can be harmful.
5. Lenses made with 1.74 material have thermoset characteristics, which means that they will deform if heated and will not revert back to their original shape if rewarmed after cooling. Instead, they will remain warped. Other lens materials such as CR-39 also exhibit this same characteristic.
Lenses made from 1.74 can be good problem solvers for higher prescriptions, so it is important to be mindful of the material’s benefits as well as its limitations when recommending it.
Mitsui’s 1.74 Monomer Goes Green
Mitsui’s 1.74 lens material is now made with a more eco-friendly, plant-based monomer named DoGreen. After its research and development department developed this process last year using a plant-based oil to produce the monomer, the product was certified as a biomass-derived product by the USDA, as well as in Japan. Now, as of October 2015, every 1.74 lens material sold by Mitsui is made with this plant-based monomer. Further development is planned for more plant-based monomers, according to the company, which stated, “The Mitsui Chemicals Group will continue research and development of biosynthesis and plant culture technology, such as polymers derived from plants.”
Mark Johnson, ABOC, NCLC, LDO, is the director of optical services at Virginia Eye Institute in Richmond, VA.
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