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| Shady Grove Eye and Vision Care Dr. Alan N. Glazier Optometrist |
| For Appointment or General Info, Contact Us At: |
| 15200 Shady Grove Road Suite 100 Rockville, MD 20850 Tel: (301) 670-1212 Fax: (301) 216-9692  aglazier@youreyesite.com |
Coatings
ULTRAVIOLET COATING
ANSI, ISO and Prevent Blindness America all recommend UV protection of 380 nm for all lenses (the upper range of UV wavelengths extends to 380 nm, not 400). The term "UV 400" is a catch phrase, more sales pitch than fact. The FDA states that plano sun lenses should transmit no more than 5 percent of UV-A below 380 nm. Keep in mind that the ANSI Z80.3 "Sunglass and Fashion eyewear Standards" are voluntary for manufacturers. UV protection can vary among manufacturers, even within the same manufacturer's lines, and it can vary with lens material. Authored by Karlen Lamparelli, ABOC, NCLC; Review of Optometry, June 15, 2001, pgs. 61-64
SCRATCH RESISTANT COATING
Scratch-resistant coatings have developed in three phases. The first came when plastic lens materials were introduced. Because plastic lenses scratch much more easily than glass, manufacturers of plastic lenses developed the first anti-scratch coating so their lenses would appeal more to consumers and dispensers alike.
Phase two in scratch-resistant coatings came in reaction to polycarbonate. Today, almost all polycarbonate lenses (and all quality polycarbonates) come with scratch-resistant coating.
The third phase is the ongoing development and improvement of the multicoatings category. Scratch-resistant coatings are the foundation of all multicoatings.
One manufacturer survey on lens damage found that 65 percent of lens scratches occur on the front surface. So, the back surface gets its share of scratches, too. That's why scratch-resistant coating gets applied to both sides of the lens.
Three types of scratch-resistant coatings exist today. Hard coats resist abrasives, slippery coats repel abrasives, and resilient coats bounce back after contact with abrasives.
Some lenses must be scratch-coated due to the nature of the substrate. Polycarbonate, because it's soft, requires scratch-resistant coating. High-index lenses in 1.60 and higher indices likewise almost always get anti-scratch coated. Authored by Karlen Lamparelli, ABOC, NCLC; Review of Optometry, June 15, 2001, pgs. 61-64
ANTI-REFLECTIVE COATING
AR coating incorporates several layers of mineral deposits, which are usually applied to both lens surfaces. The various manufacturers and AR coating companies determine the number of applications for their signature techniques. Some apply AR only to the back surface. This helps cut down on front surface scratches and still reduces reflected glare. This is especially true with polarized lenses.
AR helps reduce glare for clearer viewing, which means less eyestrain and fatigue for the wearer. AR also improves eye contact by eliminating reflections from the lens surface; AR reduces the concentric ring effect on high-minus lenses. (Coke-bottle effect of thick lenses). Some manufacturers have said that AR can reduce the darkening effect of photochromic lenses 2-10%. However, makers of newer variable tint lenses claim they are AR compatible. Check with the photochromic manufacturer for its recommendations before having AR coatings applied.
If you plan to order a tinted AR coated lens, manufacturers recommend tinting it 10-15% darker than the desired final tint. The high-intensity cleaning process that lenses go through before AR coating is likely to reduce, remove or change tint shades. Some manufacturers advise over-tinting 15-20% then reducing the tint 5% in neutralizer or 180 degree heated water in order to reduce residual tint on the lenses before AR coating. Authored by Karlen Lamparelli, ABOC, NCLC; Review of Optometry, June 15, 2001, pgs. 61-64
PHOTOCHROMICS
The photochromic process had not been a coating, but that changed recently. In 1961 when glass photochromics were first introduced, the process introduced silver halide crystals into the glass mix. When plastic photochromics were introduced in the early 1990's the process deposited the photochromic coat onto the lens surface or in wafers within the substrate.
The newest process applies the photochromic properties to both sides of the lens surface, and can produce a variety of colors for task enhancement, such as sports-specific tints that highlight the yellow of a tennis ball. Or a patient can wear them just to make a fashion statement. Authored by Karlen Lamparelli, ABOC, NCLC; Review of Optometry, June 15, 2001, pgs. 61-64
