Ultraviolet Radiation

PHYSICAL PROPERTIES OF ULTRAVIOLET RADIATION:

         Ultraviolet (UV) radiation is electromagnetic radiation
with a frequency range of 7.5 3 1014 to over 1015 Hz and
wavelengths from 400 to below 290 nm. The frequency of
UV radiation lies between that of x-rays and visible light . UV radiation is divided into three bands—UVA, UVB, and UVC—with wavelengths of 320 to 400, 290 to 320, and less than 290 nm, respectively. UVA, also known as long-wave UV, produces fluorescence in
many substances, whereas UVB, or middle-wave UV, produces
the most skin erythema. UVC, or short-wave UV, is
germicidal. Because UV does not produce heat, it is thought
to produce physiological effects by nonthermal mechanisms.
The most significant source of UV radiation is the
sun, which emits a broad spectrum of UV, including UVA,
UVB, and UVC. Both UVA and UVB reach the earth from
the sun; however, UVC is filtered out by the ozone layer.
Patients can be treated with UV of specific wavelength
ranges using a UV lamp.

The physiological effects of UV radiation are influenced
not only by the wavelength of the radiation but also by
the intensity of radiation reaching the skin and its depth
of penetration. The depth of UV penetration is affected by
the intensity of radiation reaching the skin, the wavelength
and power of the radiation source, the size of the
area being treated, the thickness and pigmentation of the
skin, and the duration of treatment. When a patient is
treated with a UV lamp, the intensity of UV radiation
reaching the patient’s skin is proportional to the power
output of the lamp, the inverse square of the distance of
the lamp from the patient, and the cosine of the angle of
incidence of the radiation beam with the tissue .
Thus the intensity reaching the skin is greatest when a
high-power lamp is used, when the lamp is close to the
patient, and when the radiation beam is perpendicular to
the surface of the skin.

         Penetration is deepest for UV radiation with the highest
intensity, longest wavelength, and lowest frequency.
Thus UVA penetrates farthest and reaches through several
millimeters of skin, whereas UVB and UVC penetrate less
deeply and are almost entirely absorbed in the superficial
epidermal layers. The penetration of UV radiation is less
deep if the skin is thicker or darker.

           UV radiation exposure produces skin erythema, tanning,
epidermal hyperplasia, and vitamin D synthesis.
Recent research supports that these effects are the result of
absorption of electromagnetic energy by the cells of
exposed skin, inducing apoptotic cell death and immune
suppression.3 UVC radiation is also bactericidal.

CLINICAL INDICATIONS FOR ULTRAVIOLET RADIATION:

           The earliest modern clinical use of UV radiation, for
which Neils Finsen was awarded the Nobel Prize in 1903,
was for the treatment of cutaneous tuberculosis. In the
1920s and 1930s, the use of UV radiation for the treatment
of skin disorders, including psoriasis, acne, and
alopecia, became very popular; however, with the advent
of antibiotics and other medications, the role of UV
radiation in dermatological medicine decreased. At this
time, UV radiation is used primarily for the treatment of
psoriasis and other dermatological conditions, including
scleroderma, eczema, atopic dermatitis, cutaneous T-cell
lymphoma (mycosis fungoides), vitiligo, and palmoplantar
pustulosis.These treatments may be applied in
conjunction with a range of topical medications.32 UV is
also used occasionally as a component of treatment for
chronic open wounds.Although the clinical
application of UV radiation in the treatment of skin
disorders is within the scope of physical therapy,
such treatments are generally provided by dermatologists
or their assistants. Treatment of chronic wounds
with UV radiation, however, generally is provided by a
physical therapist.

DETERMINING MINIMAL ERYTHEMAL DOSE OF ULTRAVIOLET FOR AN INDIVIDUAL: