 |
Even though summer
has drawn to a close, photochromic lenses are a great option
for patients year round.
Photochromic lenses
were first introduced in 1966. While glass lens was in its
molten state, a photochromic dye made from silver halide was
mixed in. In its non-activated state, the dye was clear.
When the molecules of silver halide were activated by
ultraviolet light, it caused them to change shape and to
absorb more visual color. Patients experienced visual
comfort as the lenses darkened outdoors and became clearer
inside while being protected from the ultraviolet rays of
the sun.
These new lenses
were not without room for improvement. In instances where
there was a noted difference in prescription between the two
lenses, the stronger, thicker lens would darken both quicker
and to a more intense hue than its weaker counterpart, and
the lifespan of the photochromic performance was short
lived, often accompanied by a constant tint to the lenses
indoors.
|
Manufacturing
methods and lens materials improved. The lighter weight of
plastic was a welcome change from glass. Lenses were now
submerged in a bath of silver halide, causing it to be
absorbed much further into the lens. This remedied the issue
of a lens changing at a different rate and to a different
hue than its mate.
Photochromic
technology has been embraced by many manufacturers, and is
available in almost all lens materials. Photogrey and
Photobrown glass lenses as well as Thin N' Dark high index
glass, Sunsensors mid-index plastic photochromics by Corning
Medical Optics, Kodak Instashades, and Fototec by Tifosi
among others.
Transitions® Optical,
Inc. became the first to commercialize a plastic photochromic
lens using proprietary surface treatment technology. It is
not surprising that Transitions are the most recognized
plastic photochromic line by both patients and eye care
professionals.
Active patients of
any age will benefit from photochromic lenses, but they are
extremely well suited for children's wear. Eyeglasses,
sports, and swim goggles are all available with
polycarbonate Transitions lenses. Eighty percent of a
person's UV exposure happens before the age of 18.
Instilling healthy habits includes protecting children's
eyes from UV rays. The color changing capabilities of the
photochromic lenses often fascinate children, causing them
to be more involved with the care and wearing of their eye
wear.
As photochromic
lenses become more common, types of photochromic lenses are
getting as specific as the activities they can be used for.
There are color options that provide optimum contrast for
golf, tennis, even hunting. Aside from the fact that
photochromic lenses serve a dual purpose of indoor and
outdoor eye wear, they also serve a therapeutic purpose as
well. Patients with unique visual needs may benefit from
Corning's CPF lenses. The CPF lenses are a line of specialty
photochromic lenses for patients who are acutely sensitive
to light, who require more contrast, or who suffer from
ocular conditions such as retinitis pigmentosa, albinism,
photo-phobia, diabetic retinopathy and more.
Patients may inquire
about adding treatments or coatings to their photochromics.
More is not necessarily better in this situation.
Photochromic lenses are UV protected, negating the need for
additional UV filters or coatings. These lenses are able to
be tinted, but it is not recommended, as it can alter the
performance of the lens. Scratch coatings are also not
needed in most cases. Most photochromic lenses, including
Transitions, are hard-coated. More coating can affect the
clarity of the lens.
Anti-reflective
coating can be a great partner to photochromic lenses when
applied to the back side. Front side anti-reflective coating
can cause the lens not to darken to its full capacity
outdoors.
One of the most well
received advancements in photochromic lenses is the
Drivewear, by Transitions and Younger Optics, a photochromic
lens made specifically for driving. Most traditional
photo-phobic lenses do not darken enough when driving for
most patients’ satisfaction, and while glass photochromic
lenses do tend to perform better in a vehicle than plastic,
it does not lend itself to modern frame styles, and is
generally heavier than plastic.
Drivewear is also polarized, and changes between three distinct colors,
depending on the lighting condition. Each color creates
optimum contrast, clarity, and glare filtering. However,
Drivewear does not completely lighten indoors. Its default
color is a greenish yellow suited for overcast skies.
Currently, Drivewear is only available in hard resin in
plano, single vision, and IMAGE progressive, but a wider
selection of lens materials as well as multi-focal options
will soon be available.
Even with the
advancements of photochromic lenses, there are still factors
that influence the functionality of the lens.
Temperature:
Photochromic lenses turn darker in colder temperatures, and
retard the rate that the lenses lighten indoors. In warmer
climates, the opposite is true; the lenses change quickly,
but do not darken to such a degree.
Lens Material: The
photochromic element in glass lenses will retain its
performance over time. Plastic lenses will display a slight
slowing of photochromic darkening over time. Plastic is
often more suitable for modern frame styles and to create a
lighter weight material.
Even though there
have been great advancements in the technology and
performance of photochromic lenses, they are still not a
substitute for dedicated eye wear. Both plastic and glass
photochromic lenses do not get as dark as sun lenses are
able to, and only a few photochromic lenses are available
polarized. Sun wear can be personalized to the patient's
personal taste with mirrored coatings, and task specific
lenses (polarized and non-polarized).
Dedicated sun wear
and photochromic eye wear can provide patients with
comfortable and stylish ways to protect their eyes from both
bright light more importantly, ultraviolet light. It is our
responsibility as eye care professionals to educate patients
on what type of lens and what lens options are best for
their lifestyle. |
