ULTRAVIOLET RADIATION

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Electromagnetic radiation is composed of electric and magnetic fields perpendicular to each other .Electromagnetic radiation can propagate without the need of medium, all living organisms are continuously exposed to electromagnetic radiation from sun, electric appliances, computers.Electromagnetic radiations are categorized according to there freq. and wavelength which is inversely proportional to each other.All nonionizing radiation can't break molecular bonds or produces ions, and can therefore be used for therapeutic medical applications.Higher freq. electromagnetic radiation such as x-rays and gamma rays is ionizing and can break molecular bounds to form ions.Ionizing radiation can also inhibit cell division and is therefore either not/or used in very small doses for imaging or to destroy tissues.

Ultraviolet radiation:Is electromagnetic radiation with freq. Range of with freq. range of 7.5 x 1014 to 1015 Hz and wave length from 400 nm to below 290 nm.UV radiation lies between visible light and x-ray UV radiation is divided into three bands:UVA: 400-320 nmUVB: 320-290 nmUVC: less than 290 nm

UVA: also known as long wave UV, is non ionizing and produce fluorescence in many substances.UVB: or middle wave UV is also nonionizing, it produce the most skin erythema.UVC: short wave UV, is ionizing and germicidal.

Both UVA & UVB reach the earth from the sun, however, UVC is filtered out by the ozone layer.

The intensity of UV radiation reaching the skin is greatest when a high power lamp is used, when the loop is close to the pt. and when the radiation beam is perpendicular to the surface of the skin. Penetration is deepest for UV radiation with the highest intensity, longest wave length and lowest freq. thus UVA penetrate farthest and reaches through several millimeters of skin, while UVB and UVC penetrate less deeply and are almost entirely absorbed in the superficial epidermal layers. The penetration of UV radiation is also less deep if the skin is thicker or darker.

Effect of UV radiation:1. Erythema production: erythema or redness of

the skin due to dilatation of the superficial blood vessels caused by the release of histamine, is one of the most common effects of exposure to UV radiation, UVB is most portent than UVA, the precise mechanism is unknown, however, it is known that this effect is mediated by prostaglandin release from the epidermis, and it may be also related to DNA damaging effect of UV radiation.

2. Tanning: a delayed pigmentation of the skin occur in response to UV radiation exposure. This effect is the result of increase production and upward migration of melanin granules and oxidation of premelanin in the skin.

Effect of UV radiation .. cont:3. Epidermal hyperplasia: a thickening of the

superficial layer of the skin, occurs 3 days after exposure to UV radiation. This effect is thought to be caused by the release of prostaglandine precursors leading to increasing DNA synthesis by epidermal cells, resulting in ↗ epithelial cell turnover and cellular hyperplasia.

4. Vitamin D synthesis: UV irradiation of the skin is necessary for the conversion of provitamin D to vitamin D, rickets can be result of inadequate exposure to UV, inadequate intake of vitamins or poor kidney function. For most indivuals the exposure to UV or sunlight is sufficient to maintain adequate level of vitamin D production, UV exposure may be inadequate in some bedridden pt.

Ultraviolet irradiation induces keratinocyte proliferation and epidermal hyperplasia through the activation of the epidermal growth factor receptor

Clinical indication fot the use of UV radiatiuon:1. Psoriasis: the therapeutic effect of UV radiation in the ttt of

this conditions thought to be due to it’s ability to inactivate cell division on inhibition the DNA synthesis and mitosis of hyper proliferating epidermal cells.

2. Wound healing: UV may be used for ttt of wound that have not respond to or are inappropriate for other types of ttt UVC may be used to enhances epithelialization, destroy bacteria, cause minimal erythema or tanning ( but has low carcinogenic effect). UV thought to facilitate wound healing by increasing epithelial cell turnover, causing epidermal cell hyperplasia, accelerating tissue formation, increasing blood flow, killing bacteria, increasing vit. D production and promoting sloughing of necrotic tissues.

3. Other indications: scleroderma, eczema, atopic dermatitis and vitiligo.

Contraindication for the use of UV radiation:1. Irradiation of the eyes: should be

avoided because it can damage the cornea, the eyelids and the lens.

2. Skin cancer: because it is known to be carcinogenic. Not to be used in pt. with pul. Tuberculosis cardiac, kidney or liver diseases.

3. SLE and fever; this conditions may be exacerbated by exposure to UV radiation.

Pterygium

Precaution for UV use1. Photosensitizing medications: care should be taken when applying UV radiation

to pt. who are taking these medicament; include ( sulphanamide, tetracycline, quinolone,gold therapy, amiodarone, phenothiazines and psoralen.)

2. While the pts. Are taking these medicaments they have increased sensitivity to UV radiationresulting in decrease in the minimal erythemal dose & an increase risk of burning.

3. Photosensitive pts.: some pts. Particulary those with fair skin and hair coloring and those with red hair are particulary sensitive to UV exposure, because they have accelerated & exaggerated skin response( low level of UV should be used when determining the minimal erythemal dose and for ttt.

4. Pts. who have had recent X-ray radiation; because the skin is more susceptible to develop malignancies.

5. No dose of UV should be repeated until the effects of the previous dose have disappeared. To minimize the risk of burns or an excessive erythemal response.

Adverse effects of UV:1. Burning: will occure if too high dose is

used. Can usually be avoided by carful assessment of the minimal erythemal dose prior to initiating ttt and by avoiding further exposure when signs of erythema form a prior dose are sill present.

2. Premature aging of skin: chronic exposure to UV radiation, including sunlight is associated with premature aging of the skin. The skin may dry, coarse, leathery appearance with wrinkling and pigmentation abnormalities, may be due to collage degeneration that accompanies long term exposure to UV radiations.

A 69-year-old man who drove a delivery truck for 28 years shows damaged skin on the left side of his face

Adverse effects of UV ..cont:3. Carcinogenesis: prolonged

exposure to UV may be a risk factor for the development of basal cell and squamous cell carcinoma and malignant melanoma.

4. Eye damage: UV of the eyes can cause photokeratitis, conjunctivitis and cataract.

Application techniques:How to determin the minimal erythemal dose (MED): the smallest dose producing erythema with 8 hs after exposure that disappears within 24 hs after exposurs.

1. Place UV opaque glasses on the pt. and clinician.2. Remove all clothing and wash an area of the body

least exposed to natural sunlight. The areas usually used are the volar forearm, abdomen or the buttocks.

3. Take apiece of cardboard approximately 4 x 20 cm and cut four square holes 2 x 4 cm in it.

4. Place the cardboard on the test area drape the area around the cardboard so that the surrounding skin will not be exposed.

Application techniques ..cont:

5. Setup the lamp 60-80 cm away from and perpendicular to the area to be exposed.

6. Cover all except one of the hole in the cardboard.7. Turn the lamp ON, when it reach full power, direct the

beam towerd the area to be exposed and start the timer.

8. After 120 sec uncover the 2nd hole .. Then after another 60 sec uncover the 3rd hole .. Then after 30 sec the 4th .. After another 30sec turn the lamp OFF.

According to this protocol the 1st hole has been exposed for 240sec, the 2nd = 120sec the 3rd = 60sec and the 4th = 30sec.The pt. should be observed during 24 hs mild reddening of the skin after 8 hs that disappear within 24 hs was treated with the minimal erythemal dose (MED).