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Impact ultraviolet radiation on the eyes

01 May 2009
Prevention of eye injuries UV radiation
 
 
With proper selection of prevention of the patient may avoid eye and skin lesions.
 
The expected increase in life expectancy, thinning of the ozone layer, increase the time spent outdoors increases the incidence of pathologies associated with UV light.
 
UV radiation and ozone
 
The sun - the main source of UV radiation. In the atmosphere of UV light present a part of solar radiation. Geographic latitude, altitude, cloudiness, time of day, time of year - all of these factors affect the intensity of radiation reaching the Earth's surface, and including the eyes. For example, Atlanta (Georgia) and El Paso (TX) are at the same latitude, but El Paso receives approximately 38% of UV radiation more as is at higher altitude and climate of land there. Another example: Alaska receives 10 times less UV radiation than Hawaii because Hawaii is closer to the equator.
 
Plot of UV radiation in the electromagnetic spectrum is preceded by "seems" light wavelengths of UV light are in the range of 100-400 nm. Near UV range (UV-A) is the area range from 315 to 400 nm, average area of ​​the spectrum (UV-B) - from 280 to 315 nm UV-C radiation covers the range from 200 to 280 nm, from 100 to 200 plot located nm vacuum ultraviolet radiation, the most toxic areas of the spectrum of UV radiation. Fortunately, ozone located in the stratosphere, fully delays vacuum ultraviolet light and UV-C radiation that do not reach the earth. However, growth abnormalities the incidence of skin and eyes in recent decades, perhaps in part due to the weakening or the depletion of the protective ozone layer over some regions of the planet.
 
The highest intensity of UV radiation at the Earth's surface recorded Observatory Mauna Loa (Hawaii), located at high altitude (300 meters above sea level) and close to the equator. This unique position allows the observatory to monitor the state of the ozone layer of the atmosphere.
 
The presence of "holes" in the ozone layer was set at 80 years and at the same time stressed the close relationship between the intensity of UV radiation at the Earth's surface and the thickness of the ozone layer.
 
Although the maximum numbers thinning and "holes" have been recorded over Antarctica, ozone fall noted above and Hawaii (200 Dobson units (units of ozone concentration)) - in December 1994 against 249 units in December 1964). The intensity of UV radiation with a wavelength of 295 nm, which reaches the Earth's surface through this "hole" has tripled in that time.
 
Restoring ozone will be very slow, and the initial values ​​are unlikely to be achieved by 2050. Expect that all countries, especially developing countries, will strictly adhere to the terms of the Montreal Protocol - is to be far from reality. It's no secret that, for example, India and several other countries widespread illegal large-scale production HFK (chloro-fluoro-carbons), which is active contraband imports of manufactured products. In the US HFK can not legally be made, but significant tax-exempted HFK still used in older refrigeration systems (such as air conditioners used cars). Taxes HFK so high that huge amounts of toxic gases contraband imported into the US (by volume smuggling second only to smuggling of prohibited pharmaceuticals). While maintaining production at current levels HFK projected reduction in the concentration of ozone in the stratosphere will be 6 percent in the next few decades. In that case, you should expect an increase in the incidence of UV-induced pathologies eyes and skin.
 
There is plenty of evidence linking UV radiation and skin lesions. Research related eye pathologies connection with UV radiation less, but recent work suggests that UV light is dangerous for the eye. It is shown that tangentially directed light passes through the anterior chamber from the outside to the nasal area of ​​the eye. Because a large refractive corneal peripheral part in the nasal corner of the eye creates approximately 20-fold excess intensity of the ambient UV radiation intensity of the UV radiation falling on a horizontal surface. Although damage to the nerve endings corneal epithelium - the main source of symptoms in fotokeratyt, stroma and endothelium also damaged by UV radiation.
 
There is strong evidence that UV radiation causes degenerative changes in the cornea, known climatic keratopathy point or spheroidal degeneration. Precision keratopathy may develop much earlier than previously thought. In one recent study described the recurrence of the disease in two different cases later 3.5 years after transplantation of cornea.
 
In another study shows a link between the incident UV radiation and increased polimehalii pleomorfizm and endothelial cells of the cornea when comparing groups working outdoors with the control group. Similar results were obtained in the group of welders (the average length of service with welding - 17 years) who have also polimehalii growth of endothelial cells (control - a person of the same age without experience with welding). Because artificial sources of UV radiation should not be discounted in the analysis of potential risk factors.
 
It is shown that cataracts are more common in women of all ages than men, and this difference increases with age. In one of his last works, these data are confirmed.
 
Sex differences in the genesis of cataracts can be important and need further study. Probable explanation for the increased incidence of cataracts in older women - to change the way of life in this century and the growth of insolation due to the great time spent by women outdoors.
 
 
Cancroid
 
On the relationship between solar radiation and skin cancer has long been suspected. At the end of the last century, it was shown that the sailors are chronically exposed to sunlight, a so-called "skin sailors". At the beginning of the century found an increased incidence of skin cancer among farmers and people with fair skin.
 
The effects of UV radiation on the skin - erythema, blistering, peeling, and finally tan - pretty well studied past few decades. While people are free to carry low-dose exposure to UV radiation, the immune system of the skin that provides the tolerance really suffer. It is believed that ymmunohenetycheskye factors also increase the risk of UV-induced skin cancer.
 
Chronic UV radiation effects accumulate. This means that an increase in life expectancy and increases the risk of skin cancer. With chronic UV-B radiation associated basal and squamous cell carcinoma, constituting 90% of all surface cancers.
 
The incidence of basal skin cancer in the US is growing rapidly. In the period from 1983 to 1994, the incidence of basal skin cancer in the US increased by about half. Melanoma skin is about 5% of all skin cancers, but in the structure of deaths from skin cancers of all types is already 75%. The incidence of melanoma is also growing rapidly. For 30 years from 1961 to 1991, the risk of developing melanoma in their lifetime increased 5 times and continues to grow.
 
Melanoma are highly malignant and cause significant mortality. These tumors are probably more related to acute exposure with considerable intensity (sunburn) and overexposure in childhood than with chronic UV-B-tion radiating throughout life.
 
In some people the risk of skin cancer than others. These are people with fair skin, and patients who work with chemicals and taking medications that increase sensitivity to UV radiation.
 
Preventive measures
 
Options for protecting the eyes from UV light a lot. UV-protective lenses. Most contact lenses sold today, freely pass UV radiation. Fortunately, some hidrohelnye and rigid gas-permeable lenses are made of a material with added UV blocking agent. It is useful to evaluate transmission spectra for different materials with ?? UV blocking properties because lenses absorb in the UV range differently.
 
According to Class II American National Standards Institute, contact lenses must absorb at least 95% of UV-B radiation and at least 70% of UV-A radiation to be classified as UV-protective. As the ultraviolet absorbing agent incorporated into the material, the percentage of UV radiation reaching the eye will depend on the thickness of the lens.
 
So, choosing a lens with the smallest thickness of all the particular series, you can decide whether this series of standards of protection. Furthermore, given standard requires that UV blocking lens whole, not its individual parts.
 
Diameter rigid gas permeable lenses most smaller than the diameter of the cornea. Therefore, these lenses with UV blocking properties, of course, provide less protection than soft lenses hidrohelnye. For example, the selection hazopronytsaemoy rigid lens diameter of 9.0 mm to 11.5 mm diameter cornea only 60% of the corneal protected from UV radiation, and the critical stem cells located on the limb, very poorly protected or not protected at all. Despite this and the fact that the absorption of rigid gas-permeable lenses in the UV range far from optimal, wearing such a lens is still better than a lens that does not provide UV protection.
 
Hidrohelnye lens cover limb, and the right kind of UV protection plate protects the entire cornea and, consequently, the internal structures of the eye. It is important that hidrohelnaya soft lens with UV blocker also protects epithelial stem cells located on the limb, and a layer of cells palisadnyh Vogt.
 
Corneal Epithelium - very dynamic structure. To ensure the normal thickness of the epithelium and physiologically healthy state needs a constant flow of "fresh" epithelial cells from the limbus and conjunctival cell layer palisadnyh Vogt. This concept is known as the XYZ-theory. The epithelium together with stem cells - the most sensitive to UV radiation structure of the cornea. Because the lens, protecting lymbalnoy region is the best.
 
Thus most of the UV-induced pathologies can be prevented. The physician should inform patients about the dangers of UV radiation.
 
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