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 disease. Although the
effects of sun damage may not become apparent until much later in life, the
first decade of life, when the lens of the eye is most transparent, may represent the period of greatest exposure. And, 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.
CHANGES IN LENS TRANSPARENCY FROM BIRTH
TO AGE 25 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
THE RISKS—LIGHT AND
Light or electromagnetic radiation
is categorized by wavelength. The
optical spectrum includes ultraviolet, visible and infrared light.
- Ultraviolet (UV) light has a wavelength shorter than 400nm; some
believe that wavelengths to 450nm
- Visible light wavelengths range
from approximately 380nm to
- Infrared (IR) light has wavelength
longer than 760nm.
Ultraviolet—UV light is further subdivided into UVA, UVB and UVC.
The shorter ultraviolet wavelengths are most harmful.
- 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. The proceedings from the
National Academy of Science states that compared to UVB, UVA rays cause
a larger number of mutations in the deep layers of skin where tumors
- UVB ranges from 290 to 320nm, cause 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 290nm 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 390nm. It is estimated that 50 to 80 percent of the lifetime exposure to ultraviolet occurs by the
age of 18 years. Prior to age five, 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).
Visible light—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.
It is commonly accepted that intraocular lenses (IOLs) should incorporate
UV protection, but the benefit of tinting the IOL to block blue light remains controversial. Lenses that block portions of the visible spectrum also affect
color perception and diminish night vision. So, as more children receive
IOLs, this becomes increasingly problematic. Adequate lighting is essential to
proper visual development, yet that same light may increase the eventual likelihood of retinal damage.
wavelengths have been
thought to be the least
damaging as much of
infrared light is absorbed by the cornea
and lens, and does not
reach the retina. However, there is a suggestion that damage to the eye may occur from a combination of IR and UV.
RECOMMENDED LENS MATERIALS AND COLORS
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.
Because of its effect on blue light, brown lenses also are beneficial. As
more research documents the damaging effects of blue light, the need for a
brown lens becomes increasingly evident. Children at higher risk for macular degeneration may also benefit from a golden-brown, melanin lens. An
absorptive value of 70 percent is also recommended for all brown lenses
used on children.
Although gray and brown lenses are considered “all-purpose” lens colors,
other colors may be used for special situations. For example, a medium density vermillion (cranberry color) lens is ideal for early morning snow play. This
lens color increases depth perception by filtering haze and reducing glare.
Not all lens colors are appropriate for pediatric application. While gradient tints and fad colors such as pink, blue and yellow may look cute and offer
some UV filtering benefit, they often reduce acuity and affect color rendition. Gray-blue lenses and green lenses are also discouraged for the same reasons. The addition of blue to a gray lens increases lens density (darkness) to
an unacceptable level. A green lens will filter some blue light, but the lens
has to be darkened significantly to offer comparable visual transmission to
gray or brown lenses. Gradient lenses do not offer sufficient protection from
reflective ground surfaces to be considered for use on children.
While polarized lenses are beneficial under most conditions, they may
not be appropriate for young children first learning to snow ski. While
adult downhill racers use polarized goggles, children may need some
glare and contrast for safe surface discrimination. While playing in the
snow, it is most important to reduce UVA and UVB while reducing glare,
since about 80 percent of the UV hitting the snow is reflected.
Blue Light (500 nm)
Transmission by Age
What a child sees and what a child doesn’t see
may have lasting and very damaging effects.
Macular degeneration is a group of diseases characterized by a
loss of central vision. The primary causes of macular degeneration are exposure to UV and the blue wavelengths radiation. In
the United States, retinal diseases are the leading cause of blindness and macular degeneration is the leading retinal disease. The
Eye Disease Prevalence Research Group estimates that by the
year 2020, approximately three million individuals will have significant symptoms associated with age-related macular degeneration. UV and blue light is suspected of causing irreversible damage and most exposure occurs before the age of 10 years. Cataract A cataract is opacity of the lens and is the leading cause of blindness worldwide. By 80 years of age, over half of all Americans
have cataracts. Exposure to ultraviolet light has long been associated with the development of cataracts.
A pterygium is a fleshy growth usually found
on the conjunctiva at the inner corner of the
eye. Ultraviolet light exposure (both UVA and
UVB) appears to be the most significant factor in the development of pterygia. This may
explain why the incidence is vastly greater in populations near
the equator and in persons who spend a great deal of time outdoors.
SPECIAL EDGING CONSIDERATIONS FOR HIGHER POWER
The use of polycarbonate or Trivex lenses is not the only safety consideration when fitting children with prescription sunwear. While these lenses
may protect the eye from injury, children can be injured when the frame
and/or lenses are driven into the face. While accidents are inevitable, the
damage can be lessened with the use of appropriate edging techniques.
Any portion of the lens that exceeds the interior eyewire of the frame
poses a potential safely hazard. For plus lenses, this usually will be the
upper nasal area of the glasses. Since aspheric plus lenses provide flatter
curves, they are easier to edge and often produce a safer, more attractive,
and more comfortable sunglass. However, even non-aspheric plus lenses should be surfaced for minimum thickness.
Surfacing a plus lens is more costly than using a stock lens; but, when
dealing with the smaller eye sizes required for children, it is essential. Cutting a lens for 40
eye frame out of a
70mm blank, will create
a much thicker edge
and a heavier lens than
ordering lenses from a
surface lab, the desired
thickness must be carefully considered and always specified. The suggested minimum edge thickness for a plus lens is 1.3mm and should not
Split bevels are also effective in reducing the amount of lens exceeding
the interior eyewire. Reasonable splitting of the bevel is helpful in preventing or reducing injury.
Special care must also be taken with the edges of both plus and minus
polycarbonate and Trivex lenses. Instead of the standard hide-a-bevel,
the edges must be rolled on all higher powers.
Fitting characteristics and consideration, by age There are certain ages with similar social and physical characteristics: The
infant/toddler, pre-school aged child and school aged child. Although
the social issues of older children differ greatly, the physical requirements
are essentially the same. Of primary concern within each aged group is
the fit of the bridge. The burden of fit is always the bridge.
Infant/Toddler—A baby’s bridge has
very little depth and can appear almost
flat. Yet, this tiny structure must support the weight of the glasses. To do so
comfortably, the bridge of the sunglass
must conform exactly to the shape of
the child’s nose. From infancy to aged
three, the depth of the child’s bridge
will increase to approximately 14mm
and continue to increase as the child matures. The primary change is to
the slope from the crest to the cheek.
The correct bridge will distribute the weight of the glasses evenly over
the sides and top of the child’s nose while avoiding contact with the
supra orbital bone and not resting heavily on the cheeks. Yet, the sunglass must be of sufficient size to limit UV exposure through the upper
eyewire or from the sides. While the eye should center vertically in the
frame, it should be large enough through the “A” measurement to allow
approximately one years growth. When fitting an infant or toddler with
sunglasses, prescription or non-prescription, the frame color will be traditional—blue for boys, pink for girls. Possible exceptions are unisex colored frames of tortoise, red or black, which can be quite striking on these
Preschool, three years through six years—Children in this age-group can be quite
independent and want to make all the decisions—decisions based solely on color. Availability will limit choices, but only
appropriate colors should be shown.
The correct bridge fit will still be the primary fitting concern. As with infants and
toddlers, the bridge shape must be one that
will distribute the weight evenly over the
sides and top of the child’s nose. The child’s nose will have more depth
than that of an infant, which will help the sunglass stay off the child’s
cheeks. The frame should be sized to allow at least one years growth and
be at least as wide as the widest part of the
School age, seven years through nine
years—By school age, children’s opinions
are beginning to be based more on their
peers and far less on their parents. Frame
color takes on a different role with this age group. Colors that were once in demand now may be firmly rejected.
While a seven year old may want a pink sunglass, she may refuse to wear
it by age eight. Whenever possible, non-gender-specific colors should be
shown to insure wearing compliance for the longest time. As the child
matures, it becomes increasing important to conform to their peers and
older children. Brand name recognition and their influence are escalating
for this age group.
Tweens, 10 years through
14 years—This is where the
fun begins. Tweens generally have fully developed facial
features, fully developed
visual systems and fully
developed attitudes and
opinions. These children
want to wear what older
teens are wearing. Today’s
tweens want brand names
and their parents have more
expendable income than any
previous generation. They
are more open to frame colors based on individual coloring, like cool colors for
youth with blue undertones and warm colors for those with golden
undertones. However, only popular colors are considered.
From the age of 10 years on, the shape of the child’s nose takes on far
greater cosmetic importance. In the younger age groups, the primary
concern is finding a sunglass frame that fits the child’s bridge correctly.
But, for tweens, it is the appearance of the frame’s bridge that may determine whether or not the child uses the sunglass.
If the bridge of the frame is too high, the child’s nose will appear too
long. If the bridge of the frame is quite low, the child’s nose will appear
too short. If the bridge of the frame is wide, the nose will look too wide.
In addition to the appearance of the nose, the child’s brow-line and
facial shape take on greater importance. Cosmetically, the sunglass frame
should balance the child’s face. Approximately one-third of the face
should be visible above the upper eyewire, the sunglass frame should
cover one-third of the face and one-third of the child’s face should be
visible below the sunglass.
The sunglass frame should be as wide as the widest part of the face. If
the sunglass is too narrow through the “A” measurement, it will look too
small, not offer adequate sun protection and the face will appear too full.
A sunglass frame that is too wide may be uncomfortable, make a narrow
face appear narrower and overwhelm small features.
Since the lenses of a sunglass are dark, the relationship of the sunglass
frame to the shape of the brow is less critical than in conventional eye-wear. However, the upper eyewire must offer sufficient coverage to block
uncomfortable glare and harmful sunrays, while maintaining the approximate 1/3, 1/3, 1/3 proportions.
Getting the word out—Eyecare professionals need to become advocates
armed with knowledge. At the very least, babies less than six months of
age 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 have Rx sunglasses, clip-on sunglasses or
photochromic lenses. Those children spending long periods at the
beach, on the water or playing in the snow, should have sunglasses
specifically designed for those activities.
Recommending from the chair—No advertising can compare in effectiveness to a recommendation from the doctor and all ECPs need to be
sunwear advocates. When eyecare professionals recognize the need for
sunglasses and pass that information on to the parent, more often than
not, the parent follows through.
Currently in Australia, schools require hats, sunscreen and sunglasses
for children playing outdoors. Started in 1981, Australia’s most recognizable health campaign is “Slip-Slop-Slap,” which recommends the use
of sunglasses, protective clothing and sunscreen before going out in the
sun. The original slogan of Slip on a shirt, Slop on sunscreen and Slap on
a hat was extended in later years to include “Wrap—on some sunnies
In the dispensary—The dispensary should advocate sunglasses by having printed information available for the parent and small sunglasses on
display. When browsing the sunglasses selection, few adults can resist
picking up a tiny sunglass and asking, “Do children really wear these?”
Products well placed within the dispensary indicate the office and staff
are prepared to care for children.
Overcome objections—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 a
parent on a limited budget or for rapidly changing prescriptions.
While any sunglass may be lost, broken or outgrown far too soon, the
cost of replacement is minor when compared to costly cataract surgery
or the priceless human retina. As Bill Sardi of Eye Communications once
said, “Only two retinas are issued per newborn and they have to last a