As Bill Sardi of Eye Communications once said, “Only two retinas are issued per newborn and they have to last a lifetime.” The health of our children is one of our most treasured preoccupations. Even if in most cases, sight problems are detected fairly early now, there is an area that is set aside by most parents.
Since 20 years, as we all know, the global exposure to the sun rays has been increasing spreading more and more UV A, B and C on our bodies:
UVA ranges from 320 to 400nm (as defined by ISO and SAA) and represents the longest UV wavelength with the highest energy. While single doses of UVA are less damaging, an accumulation has been associated with cataracts and long term changes to cell layers, especially in the skin around the eyes. The Queensland Institute for Medical Research reports that most damage from UVA occurs before age 30.
UVB ranges from 290 to 320nm, cause sunburn and other burns to the lids. It also has been linked to cataracts and other retinal problems.
UVC ranges from 200 to 290nm would be the most harmful, if it were not filtered out by the earth’s ozone.
One area which is very sensible to the sun is our eyes.
The cornea absorbs ultraviolet light in the lower ranges. The crystalline lens of an adult eye absorbs ultraviolet light between 300 and 390nm. It is estimated that 50 to 80 percent of the lifetime exposure to ultraviolet occurs by the age of 18 years.
At birth, the lens of the human eye is almost 95 percent transparent and remains quite clear for the first decade of life. As the crystalline lens gradually loses transparency and begins to yellow, the amount of UV penetrating the lens decreases. By age 25, less than 20 percent of UV rays reach the retina.
Lens Transparency by Age
- Birth 95%
- 6 Months 80%
- 8 Years 75%
- 25 Years 20%
Polycarbonate and Trivex lenses are the most impact-resistant lenses available and are the only lenses recommended for children’s sunglasses. These lenses offer a natural UVA and UVB inhibitor and can be tinted to the desired density and color. In addition, these materials are available polarized and in photochromic. Polarized polycarbonate and Trivex lenses are an excellent choice for children.
Water, sand and cement are significant sources of reflected glare and young children are frequently exposed to all three. Today’s polarized lenses block harmful ultraviolet light and can selectively attenuate harmful blue light. Since polarized lenses reduce reflected glare, and scatter (Rayleigh’s effect) children may suffer less discomfort and have reduced eyestrain.
Photochromic lenses have come a long way over the last several years. These lenses change more readily and the versions now available in poly-carbonate fade in about half the time of the plastic counterpart. Children seldom will switch from indoor glasses to sunglasses without parental assistance and/or insistence.
Since photochromic lenses automatically adjust in proportion to the intensity of the light, they are an excellent choice for children at a time when they are most vulnerable.
Lens Colors
Absorptive lenses are classified by two variables: the lens color and the lens transmission or density. For example, a G-15 lens is gray-green in color and has a visual transmission of 15 percent. There are only two colors of lenses suggested for general pediatric use, gray and brown. The lens-of-choice for most children is gray-gray or gray-green with an absorptive value of 70 percent. The gray color of the lens provides even color transmission throughout the visual spectrum for more natural color rendition, and in polycarbonate and Trivex, offers excellent absorption of UV radiation.
The 70 percent density recommendation is sufficient to offer adequate protection without significantly reducing acuity.
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