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Dr. Kurt Skinner

3 minutes reading time (549 words)

Lens Materials

trying-glasses-on

So it’s been determined that a spectacle prescription will help you with your visual system. The type of prescription and amount of power combined with the size and shape of the eyeglass frames you choose will play a big part in how well your glasses perform for you as well as how good they look on you when you wear them.

Nearsighted corrections are thinnest in the center of the lens and get thicker out at the edges. The higher the prescription and larger the frames, the thicker that edge will be. Farsighted prescriptions are thickest in the center and get thinner in the periphery. So it’s important to choose a frame that helps to allow your eyes to center fairly well in those frames. In other words, if you choose an over-sized frame for your face, your pupils may be looking through the very top nasal part of those frames leaving the outside bottom of the lens getting thicker and causing more visual distortion.

Traditional lenses for glasses were made with crown glass. In the early 1970’s plastic materials began being perfected well enough to make optically pure lenses. This reduced the weight of the average pair of glasses by half. The continued advancement of resins led to even more densely compacted plastics such as polycarbonate and Hi-Index materials allowing even thinner and lighter lenses that become shatter-proof and inherently block harmful UV light rays.

Very few glasses are made with traditional Crown Glass anymore. In fact there are only 2 active glass lens manufacturing facilities in the country at this time. Even though glass remains the most optically pure material to make lenses, Plastic (or CR-39) now has very similar optical ratings, offers almost half the weight of glass and reduces likelihood of shattering if trauma occurs. There are coatings that harden the surface of plastic to make it more resistant to scratching and allow for the blocking of UV light rays.

Trivex is a denser plastic that creates thinner lenses than standard CR-39 plastic, is more impact-resistant, and blocks 100% of Ultraviolet rays.

Polycarbonate is the most common lens material these days. Lenses are 40% thinner than CR-39 Plastic making them much lighter to wear and inherently shield the eyes from UV rays. In addition, they are shatter-proof and cost about the same as a hard-coated plastic lens. Obviously this makes it a perfect choice for children’s lenses.

To really make your lenses the thinnest and lightest possible, Hi-Index plastics are employed. This category of lens material represents the highest technology of plastic engineered. They are still lightweight, block the UV light rays, and are essentially shatterproof. This is the best material for the type of Rimless Frames that are mounted with screw posts drilled right through the lens.

All of these materials have coatings available to make them photochromic—or to have the ability to change in darkness in response to sunlight. And newer technology is always being developed to mold the shape of the lens to provide the best optical power for the correction the patient needs.

Your Doctor and Optician at Brookside Optometric Group can help educate you and guide you to a frame that best fits your facial features as well as accommodating the prescription you need in an eyeglass that is contemporary and attractive.

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