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Light - Sight and Ultraviolet Radiation

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By: Bud Decot (1925-2014)


What effect does radiation, (i.e. visible light and ultraviolet radiation), have on the human eyes? How can the damaging effects of light on the eyes be minimized?

There are a few questions all of us should be concerned about and know the answers to.

First, let's define light, for the purpose of this article, using the "wave length theory". In this theory, light is defined as energy coming out of atoms in timy bursts called "photons" which travel in wavy motions. Light is classified according to wave length as measured between crests. The shortest and most energetic is violet. If you were to shine a beam of light through a prism, you would produce the rainbow spectrum of visible light which is always in the same sequential order: violet, indigo, blue, green, yellow, orange and red. This band of light rays, measuring from 400 to 700, nanometers produces every color and shade visible to the human eye.

What about wavelengths shorter than 400nm and those longer than 700nm? Wavelengths shorter than 400 nm are called Ultraviolet Rays and are not visible to the human eye. Wave longer than 700 nm are called Infrared Rays and are also not visible. It is important to understand to understand that just because these rays are invisible does not mean that they do not effect, strain, or damage the eyes. On the contrary, there are profound effects upon the eyes.

Let's consider some of the effects of Ultraviolet Radiation (UV) on our eyes. The high energy photons of UV cause sunburn, snow blindness, and the "welder's flash". Prolonged exposure of the eye to UV can cause damage to the cells of the cornea (front protective covering of the eye) resulting in corneal ulcers.

Until recently, the medical profession believed that most UV, not already absorbed by the Earth's ozone layer, was absorbed by the cornea before entering the eye and the optical eyeglasses had little effect on this process. It has been determined that only a portion of the UV is absorbed by the cornea. Research has demonstrated that the human cornea absorbs UV measuring 286-320 nm (UVB). However, the part of the UV spectrum measuring 320-400 nm (UVA) is the most damaging type of UV radiation, and it is the UVA that travels directly to the crystalline lens of the human eye. UVA can cause extensive damage to our eyes when we are exposed to hours of sunlight.

Prolonged bombardment of the eyes by UVA radiation results in photochemical eye damage and as the eye ages, penetration of UVA increases. Over a period of time UVA exposure causes the generation of large amounts of pigments which results in Brown or Sun Shine cataracts. A cataract is evidenced by the clouding of the crystalline lens of the eye resulting in an inability of the lens to pass light through to the retina. It might be mentioned here that after cataract surgery the eye has no lens to absorb UVA radiation and the damaging rays can then travel directly to the retina and cause extensive damage.

The results of the research outlined here have been brought forth technical advances in the optical industry to further protect our eyes. Decot-Hy-Wyd, Inc. has all the necessary equipment to service its customers with protection against Ultraviolet Radiation.  All Decot lenses sold since 1986 have Ultraviolet protection, which eliminates 95% -99% of the UV rays entering the eyes.  

I might add here that the sun is not the only source of damaging UV. UV is also emitted from florescent lights and computer terminals. Virtually all persons wearing glasses could do themselves a favor and have the UV protection process put on their lenses.

For the 44 years I have been selling sport glasses most of you know that I have personally advised my customers to use "the lightest lens shade you can wear on a bright day." This advice has been reinforced by the aforementioned discoveries that determined UV to be damaging to the eyes. When you wear a light shade of lens you are forcing your pupil to constrict, which decreases the amount of UV entering the eyes. I have long disapproved the promotion of dark glasses by the optical industry. It has been determined that dark lenses which allow the pupil to dilate, consequently permit more UV to enter the inner part of the eye where extended damage can occur. In other words, dark glasses do not protect your eyes. Light to medium tinted lenses with the new UV protection process is the ultimate answer for those who cherish their vision.

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