Nov 2016

SPECIAL FEATURE: SUMMER SPECIAL AND SUNGLASSES
NZ standard is voluntary; in fact, there is no standard
sunglasses have to meet, and the price of the sunglasses
doesn’t necessarily reflect the quality of the UV
protection. Glasses claiming they are UV400 should also
be avoided, says Gaunt, unless they also state they meet
the above standard, as there is no universally accepted
definition of what UV400 actually means.
3. Choosing frames
CONTINUED FROM P11
Just like optical glasses, your clients need to be advised
on the right sunglass frames for their face shape, lifestyle
and purpose.
Sporty-types and those who do a lot of driving or
work outside, might prefer wrap-style frames that
give a greater area of coverage and have a darker tint
or reflective lenses for added clarity outside, while
those who wear sunglasses more casually might prefer
something that fits with their own sense of style – such
as oversized frames or vintage. If your client expresses
any concerns over losing their
sunglasses or where they might keep a
second pair, then photochromic lenses
that change with the environment are
probably the better lifestyle choice.
The same style tips you’d use for
helping a patient chose prescription
lenses work for sunglasses. For example,
a rounder face would benefit from
square-shaped sunglasses to balance
their face shape, while oval faces
shouldn’t wear glasses that are too
wide. And a good thing to remember
is if your client has a strong affiliation
with a particular style of frames, they
can probably have tinted lenses fitted in
those frames too.
4. Clip ons/over glasses
For the customer who sees sunglasses
as pure necessity, the resurgence of
‘over glasses’ and clip-ons is no doubt a
dream come true. Coverspecs are wraps
that go over the top of your clients
existing glasses, and they are approved
by the Cancer Society of New Zealand –
giving protection along the side of the
frame as well as over the lens. Other
brands include Cocoons eyewear and
Horizons eyewear.
Alternatively, clip-ons – available from
a number of different suppliers – are
armless frames with sunglass lenses
that clip on to your clients’ existing
glasses. They fold up when not in use so
they don’t have to be removed (and are
less likely to be misplaced).
5. Photochromic lenses are just as useful
inside as out
Photochromic lenses, like Transitions and Hoya Sensity, are
really great for those people who just want a pair of glasses
for all occasions, without having to remember to take out
their sunnies or accessories.
“Transitions lenses are not sunglasses. But for patients
looking to find an everyday lens they can wear from
morning to night, indoors to outdoors, Transitions lenses
will be the lens to recommend,” says Stuart Cannon,
Transitions Optical general manager, Asia-Pacific.
“Outdoors, Transitions lenses block 100% UVA and UVB
rays from the sun and also help protect our wearer’s eyes
from glare and harmful blue light.”
These lenses are also useful indoors. Transitions
Signature VII lenses block at least 20% of harmful blue
light indoors – up to two times more than standard
clear lenses – while still being clear, and more than
85% outdoors. Transitions XTRActive help provide more
protection everywhere they are needed, blocking at least
34% of harmful blue light indoors and 88-95% outdoors,
according to a recent study.
Sunlight exposure
and AMD
Dr David Worsley*
Whether, and to what degree, sunlight exposure is an age-related
macular degeneration (AMD) risk factor is controversial. Although visual
perception occurs between wavelengths 380-760 nm, the retina/retinal
pigment epithelium (RPE) complex is exposed to light from 320nm and above.
Wavelengths below 320nm, including most UVA and UVB, are blocked by the
cornea and crystalline lens.
Laboratory studies provide evidence to suggest a vulnerability to sunlight
exposure. Wavelengths beween 400-760nm absorbed by retinal/RPE proteins, such
as melanin and lipofuscin, can lead to cell damage. The RPE is prone to oxidative
stress, especially from UV and blue light, with DNA damage, alteration of RPE
cell size and movement. The age-related increase in both number of lipofuscin
granules in human RPE cells and in their photoreactivity may impose a greater risk
of oxidative damage in the aged RPE, suggesting a light-sensitive mechanism in
the development of AMD. Blue light related photoreactivity of melanosomes also
increases with age. Blue
light exposure in an
experimental rat model
of dry AMD induces
retinal injury.
The retina possesses
inherent protection
against sunlight
damage via antioxidant
enymes, light
absorbing pigments
such as melanin and
flavoproteins, and the
shedding of damaged
photoreceptor outer
segments.
Epidemiological
Does UV contribute to AMD?
evidence for light
exposure as an AMD risk
factor is inconclusive
and only a few studies report a positive association. One of the best, the Beaver
Dam Eye Study (BDES), found that exposure to summer sun as teenagers through
to the thirties was associated with later development of early AMD. Estimated
ultraviolet-B exposure and historical markers of sun sensitivity were not
associated. An inverse association was found between the level of protection from
sunlight via use of brimmed hats and sunglasses and AMD, but only in men. Follow
up five-year incidence of early AMD confirmed this association; however the 10-
year incidence study showed few significant associations between environmental
light and incidence and progression of early AMD. A recent analysis of long-term
data from the BDES found some evidence that light eye or hair colour combined
with sunlight exposure is associated with increased risk of developing early
AMD. The link may be a genetically determined lower level of photo-protective
eumelanin. Other studies have similar findings; for example the Chesapeake
Bay Waterman Study found late AMD to be associated with long-term high blue
light exposure. An Australian study found that sensitivity to sunburn may be a
risk factor. In contrast to these studies, several case-control studies have failed to
show associations between sunlight exposure and AMD. Several studies showed
a lowered risk of AMD. A review of the literature in 2012 noted these conflicting
findings but by met-analysis found overall evidence in favour of an association.
We need to be cognisant of the inherent
weaknesses of epidemiology studies dealing
with a complex exposure. Issues include
challenges in measuring acute and chronic
lifetime exposure and the effect of potential
confounding variables, such as sun sensitivity
and sun avoidance behaviours. Furthermore,
each study evaluates a different population
(ethnic and genetic makeup) with different
confounding factors and located in a variety of
geographical areas with very different exposure
intensities.
In conclusion, the literature is conflicting. That
doesn’t provide a practical solution for advising
your patient. So my take on the controversy
is that the data does not support a strong
association of sunlight exposure and AMD, but
a modest effect can’t be ruled out. Therefore
it is reasonable to advise simple measures to
reduce potential risk. A wide-brimmed hat will
drastically reduce sun exposure. Sunglasses
will give additional protection. However, strict
wearing of sunglasses is not indicated, indeed
there are some circumstances where tinted
lenses may have a functional impact for an AMD
patient with reduced macular function.
ABOUT THE AUTHOR
– BUILD TO
PERFORM
VIS ION EN H ANCEMENT
EYEWEA R
* Dr David Worsley is
an ophthalmologist at
Hamilton Eye Clinic and
Waikato Hospital. He is a
retina specialist with an
interest in AMD and sits on
the medical advisory board
for MDNZ.
12 NEW ZEALAND OPTICS November 2016