Ultraviolet Rays are rays that reach earth from the sun that are too high in frequency for the
human eye to see
The reason Ultraviolet rays are not visible is that the human eye can only see between 400
Nanometres and around 800 Nanometres.
Nanometres (Nm) are the unit of measurement for light rays. The different rays are interpreted
by our eyes as different colours. Blue, for example is a high frequency light wave (400-450
Nm) and Red is a very low frequency light wave (around 750Nm).
So high frequency ultraviolet rays arrive on planet earth between 0 and 400 Nanometres.
These high frequency waves are piercing and powerful and are responsible for most skin
cancers and sun related eye ailments. They pierce the eye unimpeded. The only way of
protecting yourself from them are by staying in a shaded area or by using sunglasses which
block all UV Rays.
There are three types of UV Rays:
1. UVC--between 0 and 250 Nanometres--these harmful rays are fortunately almost entirely
blocked out by the Earths atmosphere.
2. UVB--between 250--360 Nanometres--THE BIG BADDY! These are the most harmful UV
Rays are are responsible for most damage done to human eyes. These insidious ultraviolet
rays pass right through Earths atmosphere and bore directly into the deep internal workings of
the human eye.
3. UVA--between 260--400 Nanometres--less harmful than UVB rays but still of some concern.
These rays are only blocked by lenses which block out all light up to 400 Nanometres. (Called
UV400 lenses).
INFRARED RAYS are slower, lazy waves which cannot penetrate the human eye. They simply
bounce off the surface and may be noticed, if at all, as making the eye slightly warmer than
would otherwise be the case.
Before buying sunglasses it is useful to check that the brand you are buying uses UV400
lenses.
It is helpful in summer climates to consider some side protection as “stray light” can enter via
the side on smaller lens sunglass styles. This is particularly true when skiing or boating where
UV light reflects off the surface of snow and water and enters the eye via the “side door” if it
has the chance to do so. Recent wrap-around styles popular today are useful because they
eliminate most stray light.
THE HIGH RISK
CHECK LIST:
You are at a higher risk of sun related eye problems if you...
• Partake in outdoor sports.
• Work outdoors, or with artificial
light sources.
• Live in a bright, sunny climate.
• Have had cataract surgery.
• Take photosensitive prescription
medicine (antibiotics, hypertensive medicine, tranquilizers,
oral contraceptives, etc.).
• Have been exposed to bright
sunlight since childhood.
• Wear contact lenses.
