Throughout life, environmental variables such as proximity to the equator, higher elevations, reflective ability of the ground surface and mid-day exposure, increase the risks of developing sun related eye diseases. Although the effects of sun damage may not become apparent until much later in life, a person's first decade, when the lens is most transparent, may represent the period of greatest exposure. At no other time in life are we as prone to the lasting effects of the sun's rays than in infancy.

To understand the increased risk to infants and children, we must examine the changes in lens' transparency that occur and the relationship of light to ocular damage.

At birth, the lens of the human eye is almost 95 percent transparent and remains quite clear for the first decade. As the crystalline lens gradually loses transparency and begins to yellow; the amount of ultraviolet (UV) penetrating the lens decreases. By age 25, less than 20 percent of UV rays reach the retina.

Light or electromagnetic radiation is categorized by wavelength. The optical spectrum includes ultraviolet, visible and infrared light. UV light has a wavelength shorter than 400 nanometers; some believe that wavelengths to 450 nanometers are hazardous. Visible light wavelengths range from approximately 380 nanometers to 760 nanometers. Infrared (IR) light has a wavelength longer than 760 nanometers.

UV light is further subdivided into three types: UVA, UVB and UVC. The shorter ultraviolet wavelengths are most harmful. UVA ranges from 320 to 400 nanometers, with the highest energy. UVB ranges from 290 to 320 nanometers, causes sunburn and other burns to the lids and related structures and is thought to have carcinogenic effects on the skin. It also has been linked to cataracts and other retinal problems. UVC ranges from 200 to 290 nanometers and would be the most harmful, if it were not filtered out by the earth's ozone.

The cornea absorbs ultraviolet light in the lower ranges. The crystalline lens of an adult eye absorbs ultraviolet light between 300 and 390 nanometers. It is estimated that 50 to 80 percent of lifetime exposure to ultraviolet occurs by the age of 18. Prior to age 5, there are not enough chromophores (parts of a molecule responsible for its color) in the lens of a child. Because the lens of a child is so transparent, it does not filter the ultraviolet with the efficiency of the adult eye. As the eye matures, UVA is absorbed and converted, which turns the lens slightly yellow. After a lifetime of absorption, the lens may be significantly yellow and require removal (brunescent cataract).

The length of the light wave striking the retina determines the colors that make up the visible spectrum. Blue and blue-violet light are the most damaging to the eye, especially when combined with UV or IR. While the cornea and crystalline lens absorb some of the ultraviolet, high percentages of blue light still pass through. UV and blue light cause cumulative damage to retinal and skin cells.

These longer wavelengths have been thought to be the least damaging as much of infrared light is absorbed by the cornea and lens and does no reach the retina. However, there is a suggestion that damage to the eye may occur from a combination of IR and UV.

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. These materials are available polarized or as transitions. 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 be selectively attenuate harmful blue light. Since polarized lenses reduce reflected glare, children may suffer less discomfort and have reduced eyestrain.

Photochromic lenses have come a long way over the last several years. 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 the time when they are most vulnerable.

Babies less than 6 months old should not be in the sun. Older babies should wear hats, use strollers with canopies and, whenever possible, wear sunglasses.

Children who wear corrective lenses should wear prescription sunglasses, clip-on sunglasses or photochromic lenses. Children spending long periods at the beach, water or playing in the snow should have sunglasses specifically designed for those activities.

Non-prescription sunglasses remain an inexpensive commodity, and when the need for sun protection is recognized, few parents can resist paying the price for prescription sun protection. The additional cost of photochromic lenses is justified by the added convenience. Clip-on sunglasses are inexpensive and may be the only reasonable option available to the parent on a limited budget for rapidly changing prescriptions. While sunglasses may break, get lost or outgrown, the cost of replacement is minor when compared to costly cataract surgery or the priceless human retina.

A famous quote to go by: “Only two retinas are issued per newborn, and they have to last a lifetime.”

Mark DiVietro is an optician at Silbert Optical in Auburn.