While walking along an overgrown bush trail following a friend, a branch snaps back and hits you in the eye. You experience a sharp pain and your eye tears profusely. The result is a serious corneal abrasion.
At a skeet shoot, you are concentrating on station eight, high house. After calling for the bird and powdering it, a small fragment of the clay target enters your eye and is embedded in the cornea. A foreign body injury! It must be removed.
It is a bright,sunny, early July day. You get a late start and do not hit the water until mid-morning. The walleye fishing is slow but you are a fanatic. Your sunglasses? They were left on the seat of your truck. After six hours on the water, it is time to go in. At two o’clock in the morning, you wake up to an excruciating pain in your eyes. Your eyes feel like sandpaper and are extemely light sensetive. This pain is a result of an ultraviolet burn on the front surface of an ultraviolet burn on the front surface of your eyes.
These cases are classified as ocular emergencies and they require medical attention. Depending on the severity of the abrasion and foreign body injuries, it is possible to lose an eye. The ocular ultra violet burn predisposes you to another burn in the future.
These eye injuries could have been prevented with the proper ophthalmic quality lenses and frames. The correct eyewear will protect you from foreign bodies and ultraviolet radiation. The proper lens selection can enhance contrast under varying light conditions and sharpen your vision.
We need a little background information on UVR for you to understand why protection from UVR is important. Ultra violet radiation is generated by the sun. You cannot see it, you cannot feel it nor can you rely on body temperature as a gauge for ultraviolet radiation. It is not the heat of the sun that causes sunburn, but the ultraviolet radiation. Water, sand and snow act like mirrors to reflect the radiation back to you. The brighter the surface,the more rays are reflected to you.
Dark clouds decrease the amount of radiation that reaches you, but it is not eliminated completely. Ultraviolet radiation is divided into short wavelength UVB radiation (290 to 315 Nanometers) and long wavelength UVA radiation (315 to 380 nanometers). These wavelengths of radiation are beyond the visible spectrum that the human eye can see. Ultraviolet radiation causes photokeratoconjuntivitis, commonly known as snow blindness. As well, it contributes to and accerlates the development of cataracts, causes corneal degeneration and contributes to the development of pinquecula and pterygium. Furthermore, ultraviolet radiation is responsible for the degeneration of retinal pigment epithelium.This accerlates age related macular degeneration which is a major cause of blindness in North America today. It also causes tumors of the eyelid.- malignant melanoma which is fatal in most cases.
Protection from ultraviolet radiation – both UVA & UVB – is important, because eye tissues do not develop a tolerance. People with blonde hair and blue irises are most vulnerable to UV damage. Damage to eye tissue by repeated exposure is additive, incremental and irreversible. Systemic medication such as tranquilizers,anti-hypertensives,diuretics,oral contraceptives,antipsychotics,antidiabetics and antibiotics can increase your eye sensitivity to ultraviolet radiation.
Spectacle lenses are made from three materials; 1)crown glass, 2)CR 39 resin or polycarbonate. The best safety lenses are made from polycarbonate, followed by CR 39 resin and then a treated crown glass lens. The polycarbonate and CR 39 resin lenses can have scratch resistant coatings applied to them and they are half the weight of crown glass lenses. Polycarbonate lenses more expensive than CR 39 resin lenses because they require special equipment to edge, tint and generate curves.
Contrary to popular opinion, clear crown glass and coated clear crown glass lenses provide no effective protection against radiation, though some solid, through-the-glass tints provide partial ultraviolet radiation protection. CR 39 resin lenses block UVB and, therefore, offer partial protection in their clear form. An ultraviolet inhibitor can be added to block UVA in the CR 39 material. Polycarbonate, like other high index materials, block UVB & UVA(up to 380 nm) in the clear form.
Specialty lenses such as photochromatics in glass and plastic block most ultraviolet radistion. Polarized glass and plastic lenses are making a comeback and they make an excellent filters.
The best value in ophthalmic lenses today, is the CR 39 resin material with the scratch resistant coating
So what is the best tint? It depends on light levels associated with your outdoor activity. In low light conditions, dawn, dusk, and night driving a clear lens with an anti-reflective coating is best. Clear lenses transmit 92% of incident light, 8% is lost to reflection. The anti-reflective coating increases the amount of light transmitted to 99%. The 7% increase in the amount of light transmitted is within our ”just noticeable difference” threshold criteria. This means that we can see better under low light conditions with an anti-reflective coated lens. For sitting in a deer stand at dusk or dawn or in a goose blind the anti-reflective coatings are excellent and can help you to remain hidden because, while the front surface of a regular spectacle lens acts like a mirror and reflects light, reflections are virtually eliminated with a coated lens. Another real advantage to coated lenses is that your vision will be enhanced while driving at night.
For other full-light applications, a tinted lens with ultraviolet protection is more appropriate. The color of the tinted lens is personal preference and independent of the ultraviolet radiation protection. Sunglasses work best if they absorb 60-75% of visible light. Grey lenses tend to distort colors less. Strong greens, browns and ”blue-blocking” lenses can affect color perception in people with normal color vision.
Polarized sunglasses do more than just offer ultraviolet protection. These specialty lenses eliminated ”glare” from surfaces like water and snow. Whether you are a fly fisherman, walleye, salmon or ice fisherman these lenses deserve a look. They are one of the best sunglass lenses on the market today and are available in prescription form. I would not be caught on the water or the snow without them.
Photochromatic lenses are hybrids and are unique, in that they darken on exposure to ultra violet light. They are available in glass and plastic lenses. The darkening rate is temperature dependent, and so the colder it is, the darker they become. Photochromatic lenses are excellent ultraviolet absorbers and are a good choice for outdoor winter sports. Their downfall is they never lighten up completely and that may be a problem for some people who already have difficulty with night driving.
For people who are involved in trap, skeet and sporting clays the light medium target orange(LMTO)tint brightens the background and improves clay target contrast. This makes picking up the clay target easier and quicker. For these shotgun sports, the LMTO tinted lenses should be fit into a ”Randolph” or ”Decot” frame, both of which are designed specifically for shotgun shooting. The size,shape,and frame design are important considerations in determining the level of ultraviolet protection. A large lens mountd in a wrap-around frame sitting close to your face will reduce the amount of radiation reaching your eyes from the sides and top. A broad brimmed hat and side shields give added protection.
If you need prescription lenses to correct small amounts of farsightedness, nearsightedness or astigmatism the correction should be ground into your outdoor eyewear. The resultant in focus retinal image will improve visual acuity and enhance depth perception, reduce eye fatigue and improve your visual comfort.
Properly fitted eyewear is important for all outdoor pursuits. The proper lenses can protect you physically from projectile foreign bodies and ultraviolet radiation. The correct coatings and tints can improve vision and contrast depending on the ambient light.
Eye injuries in the outdoors can be prevented with a little background knowledge and some commom sense.
Source: Hunting & Shooting Magazine