Een van de grootste zorgen bij infrarood therapie zijn de ogen. Infrarood wordt gebruikt voor de huid of het gezicht. Kan het rode licht onze ogen beschadigen of kan het juist gebruikt worden om de ogen te genezen?
Introductie
Eyes are perhaps the most vulnerable and precious parts of our
bodies. Visual perception is a key part of our conscious experience, and
something so integral to our day-to-day functioning. Human eyes are
especially sensitive to light, being able to differentiate between up to
10 million individual colours. They can also detect light between the
wavelengths of 400nm and 700nm.
We do not have the hardware to perceive near infrared light (as used in infrared light therapy),
just as we do not perceive other wavelengths of EM radiation such as
UV, Microwaves, etc. It has recently been proven that the eye can detect
a single photon.1 Like elsewhere on the body, eyes
are made up of cells, specialised cells, all performing unique
functions. We have rod cells to detect light intensity, cone cells to
detect colour, various epithelial cells, humor producing cells, collagen
producing cells, etc. Some of these cells (and tissues) are vulnerable
to some types of light. All of the cells receive benefits from some
other types of light. Research in the area has increased significantly
in the last 10 years.
we see light. Graph showing the wavelength perception range of the
light sensitive cells in the human eye. Note that the green cones can
detect light in the orange/red range.
Which Color/Wavelength of Light is Beneficial for eyes?
Most of the studies that point to beneficial effects use LEDs as the
light source with the vast majority around the wavelength of 670nm
(red). Wavelength and light type/source are not the only important
factors though, as the light intensity and exposure time affect the
results.
How does red light help the eyes?
Given that our eyes are the primary light-sensitive tissue in our
body, one might think that the absorption of red light by our red cones
has something to do with the effects seen in the research. This is not
entirely the case.
The primary theory explaining the effects of red and near infrared
light therapy, anywhere in the body, involves the interactions between
light and the mitochondria. The core function of mitochondria is to
produce energy for its cell – light therapy improves its ability to make
energy.
The eyes of humans, and specifically the cells of the retina, have
the highest metabolic requirements of any tissue in the entire body –
they require a lot of energy. The only way to meet this high demand is
for the cells to house many mitochondria – and so it is no surprise that
cells in the eyes have the highest concentration of mitochondria
anywhere in the body.
Seeing as light therapy works via interactions with the mitochondria,
and the eyes have the richest source of mitochondria in the body, it is
a reasonable assumption to hypothesise that the light will also have
the most profound effects in the eyes compared to the rest of the body.
On top of that, recent research has shown that degeneration of the eye
and retina is directly linked to mitochondrial dysfunction. So a therapy
that can potentially restore the mitochondria, of which there are many,
in the eye is the perfect approach.
Best wavelength of light
670nm light, a deep red visible type of light, is by far the most
studied for all eye conditions. Other wavelengths with positive results
include 630nm, 780nm, 810nm & 830nm. Laser vs. LEDs – a note Red
light from either lasers or LEDs can be used anywhere on the body,
although there is one exception for lasers specifically – the eyes. Lasers are NOT suitable for light therapy of the eyes.
light (even if it is red) can be hazardous to the eyes. The laser beam
can be focused by your eye’s lens into a tiny point of intense energy –
leading to burns and scars. Red LED light doesn’t pose the same risk and
so is not hazardous.
This is due to the parallel/coherent beam property of laser
light, which can be focused by the lens of the eye to a tiny point. The
entire beam of laser light can enter the eye and all of that energy is
concentrated into an intense tiny spot on the retina, giving an extreme
power density, and potentially burning/damaging after just a few
seconds. LED light projects out at an angle and so does not have this
issue.
Power density & dose
Red light passes through the eye with over 95% transmission. This is
true for near infrared light and similar for other visible light such as
blue/green/yellow. Given this high penetration of red light, the eyes
only require a similar treatment modality to the skin. Studies use
around 50mW/cm2 power density, with quite low doses of 10J/cm2 or less. For more information on light therapy dosing, see this post.
Harmful light for eyes
Blue, violet and UV light wavelengths (200nm-480nm)
are bad for the eyes, being linked to either retinal damage or damage in
the cornea, humour, lens and optical nerve. This includes direct blue
light, but also blue light as part of white lights such as
household/street LED bulbs or computer/phone screens. Bright white lights,
especially those with a high colour temperature (3000k+), have a large
percentage of blue light and are not healthy for the eyes. Sunlight,
especially midday sunlight being reflected off water, also contains a
high percentage of blue, leading to eye damage over time. Luckily the
earth’s atmosphere filters out (scatters) blue light to some extent – a
process termed ‘rayleigh scattering’ – but midday sunlight still has a
lot, as does sunlight in space seen by astronauts. Water absorbs red
light more so than blue light, so the reflection of sunlight off lakes/oceans/etc
is just a more concentrated source of blue. It’s not just reflected
sunlight that can do harm though, as ‘surfer’s eye’ is a common issue
related to UV light eye damage. Hikers, hunters and other outdoorsmen
can develop this. Traditional sailors such as old navy officers and
pirates would almost always develop vision issues after a few years,
mainly due to sea-sunlight reflections, exacerbated by the nutritional
issues. Far infrared wavelengths (and just heat in
general) can be harmful for the eyes, as like with other cells of the
body, functional damage occurs once the cells get too warm (46°C+ /
115°F+). Workers in old furnace related jobs such as engine management
and glass blowing always developed eye issues (as the heat radiating
from fires/furnaces is far infrared). Laser light is
potentially harmful for the eyes, as mentioned above. Something like a
blue or UV laser would be the most destructive, but green, yellow, red
and near infrared lasers can still potentially cause harm.
Eye conditions helped
General vision – visual acuity, Cataracts, Diabetic Retinopathy,
Macular Degeneration – aka AMD or age-related macular degeration,
Refractive Errors, Glaucoma, Dry Eye, floaters.
Practical applications
Using light therapy on the eyes before sun exposure (or exposure to
bright white light). Daily/weekly use to prevent eye degeneration.
References
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