Ultra-violet radiation (UVR) is electromagnetic energy that is invisible to the human eye, with wavelengths between 10nm and 400nm. Ultra-violet lies between visible light and x-rays in the electromagnetic spectrum.
The therapeutic part of the ultra-violet spectrum may be divided into:
- UVA ⇒ 400-315 nm
- UVB ⇒ 315-280 nm
- UVC ⇒ below 280 nm
UVA and UVB are biotic, where as UVC is abiotic.
Production of UVR
The Sun emits a broad spectrum of ultraviolet radiation, including UVA, UVB, UVC. Both UVA and UVB reach the earth from the sun. however, UVC is filtered out by the ozone layer. For therapeutic purposes, some form of generator is used to emits UVR.
Types of UVR Generators
Two types of UVR generators-
- Mercury vapor lamp– can be of two types;
- Air cooled medium pressure mercury vapor (Alpene sun lamp)
- Water cooled mercury vapor lamp (kromayer lamp)
- Fluorescent lamps
A) Mercury Vapor Lamp-
A mercury-vapor lamp is a gas-discharge lamp that uses an electric arc through vaporized mercury to produce light. These are used for the production of ultraviolet rays for therapeutic purposes.
For explanation, you may click here – Mercury Vapor Lamp for Production of UV Rays
B) Fluorescent tubes
- One of the major problems with the mercury lamp is that it produces a certain proportion of short ultra-violet rays.
- Modern treatment regimens often require the use of long-wave ultra-violet without the short wave and so various types of fluorescent tubes have been designed.
- The spectrum of each tube depends upon the type of phosphor coating. each tube is about 120 cm long and made of a type of glass that allows long-wave ultra-violet to pass.
- The inside of the tube is coated with a special phosphor.
- A low-pressure arc is set up inside the tube between its ends by a process of ionization similar to that described for the mercury vapor tube.
- Short ultra-violet is produced, but it is absorbed by the phosphor and re-emitted at a longer wavelength.
- Depending upon which particular phosphor is used, the output of the tube may be part UVB and part UVA (280-400) or UVA (360-400nm), as in the PUVA apparatus, but accurate control of the emitted wavelength is possible.
- The theraktin tunnel is a semi-cylindrical frame in which are mounted four fluorescent tubes.
- Each tube is mounted in its own reflector in such a way that an even irradiation of the patient is produced, allowing treatment of the whole body in two halves.
- Normally fluorescent tubes with a spectrum of 280-400 nm are used.
- For the treatment of psoriasis, where a large amount of UVA, is required, the fluorescent tubes are used.
- The tubes are usually mounted in a vertical battery on a wall, or four sides of a box surrounding the patient.
- This form of ultra-violet is usually given two hours after the patient has taken a photoactive drug such as psoralen: hence the term PUVA (psoralen ultraviolet A)
Absorption of UV Rays in body
The superficial layer of our body is skin. it is a protective layer of our body. it absorbs the ultraviolet light and prevent its penetration down to unprotected or weak cells.
The extent of the reaction or damage depends on the wavelength of ultraviolet and the amount of ultraviolet absorbed.
UVC is absorbed in the epidermis along with UVB, and UVA may penetrate as far as the capillary loops in the dermis.
Physiological Effects of UVR
Immediate/ acute effects
- Increased skin growth
- Vitamin D production
- Prophylactic effect
- Immunosuppressive effects
- Effects on eye
Long term/ chronic effects
- Solar elastosis or aging
A) Immediate acute effects-
Erythema is reddening of the skin as a result of an inflammatory reaction stimulated by ultraviolet rays ⇒ release of histamine like substance ⇒ dilation of the capillaries and arterioles and exudation of fluid into skin.
The Erythema reaction has been used to classify doses of ultra-violet given to patients. there are 4 degrees of erythema E1, E2, E3, and E4.
|Degree of Erythema||Latent Period (hours)||Appearance||Approximate duration||Skin edema||Skin discomfort||Desquamation||Relation to E1|
|E1||6-12 h||Mildy pink||<24 h||None||None||None||x 1|
|E2||6 h||Definite pink red, blanches on pressure.||2 days||None||Slight soreness||Powdery||x 2.5|
|E3||3 h||Very red, does not blanch||3-5 days||Some||Hot and painful||Thin sheets||x 5|
|E4||<2 h||Angry red||1 week||Blister||Very painful||Thick sheets||x 10|
- Pigmentation or tanning of the skin follows the erythema.
- Its amount varies with the intensity of the erythema.
- It is due to the increased deposition of the pigment melanin formed in the basal cell layer of the skin by the melanoblasts and migrates to the superficial layers of the epidermis.
3) Desquamation (increased skin growth):
- Desquamation or peeling is proportional to the intensity of the erythema.
4) Vitamin D production:
- UVB is able to convert sterols in the skin, such as 7-dehydro-cholesterol to vitamin D.
- Vitamin D is required to assist in the absorption of calcium and phosphorous from the intestine to blood stream.
- Suberythemal dosage of UVB are adequate to promote vitamin D synthesis.
5) The Prophylactic effects:
The resistance of the body to infection is increased as a result of the stimulation of reticuloendothelial system ⇒ antibodies against bacteria and toxins.
6) Immunosuppressive effects:
- UV destroys Langerhan’s cell and stimulates the proliferation of suppressor T cells, ( T cells are regulatory in that they inhibit antibody production)
- This immunosuppressive effects may contribute to the development of skin cancer.
- In short, UV radiation induces a state of relative immunosuppression that prevents tumor rejection.
7) Effect on eye:
- Strong doses of UVB and C radiation to the eyes can lead to conjunctivitis and photokeratitis results in
- Irritation of the eye,
- A feeling of grit in the eye,
- Watering of the eye and
- Aversion to light (photophobia).
- In severe cases intense pain and spasm of the eyelid may be present this is also known as a ‘Snow Blindness’.
- While UVB and C are absorbed in the cornea,UVA can pass through to be absorbed mainly in the lens of the eye.
- The strong doses of UVA may lead to the formation of Cataracts.
B) Long term/chronic effects-
1)Solar elastosis and ageing-
- Prolonged exposure of UVR lead to, premature ageing of the skin, this is especially so in the fair-skinned.
- Decrease function of sebaceous and sweat glands.
- Loss of elastic tissue
- The skin becomes wrinkled, dry and leathery.
- Skin cancers, basal cell, and squamous cell carcinomas.
- Carcinogenesis is a danger, as these rays may have an effect on DNA and thus on cell replication.
- Shorter ultraviolet waves should be avoided and courses of treatment should not exceed four weeks.
Skin response to UVR depends upon:
- Quantity of UVR energy applied to the skin
- Biological responsiveness of skin.
1) Quantity of UVR energy applied to the skin, which depends upon-
- Output of the lamp.
- Distance between the lamp and the skin
- Angle at which radiation falls on the skin
- Time for which radiation is applied on the skin.
2) Biological responsiveness of skin-
The following skin types are described, from the most reactive through to the least:
Calculation of dosage
- E1 is determined from the skin test and the other erythemal dosages can be calculated as follows-
- Suberthermal 75% of E1
- E2 = 2.5×E1
- E3 = 5×E1
- E4 = 10×E1
- Double E4 = 20×E1
- E4 and double E4 are used on an open wound
- Minimal erythema dose (MED)– The smallest dose of UVR to result in erythema that is just detectable by eye at between 8-24 hours after exposure is called minimal erythemal dose.
Progression of UV dosage
Dosage can be progressed as follows:
- Suberythermal – previous dose plus 12.5%
- E1- previous dose plus 25%
- E2- previous dose plus 50%
- E3- previous dose plus 75%
Dosage used on open wounds are not progressed because there is no epidermis to thickness.
Alteration of the intensity with distance
To irradiate a smaller area the source is moved nearer to the patient but the time of exposure must be altered to maintain the same intensity under the law of inverse squares.
NOW TIME = OLD TIME × (NEW DISTANCE)² / (OLD DISTANCE)²
Therapeutic Effects and Uses of UVR
The therapeutic effects produced and the uses are listed as under:
- Psoriasis is a chronic skin disease of unknown causes,
- which are manifested either as silvery scales covering the pink or red plaques (chronic discoid psoriasis), or the small lesions scattered on the trunk, postural psoriasis, generalized postural and erythrodermic psoriasis, flexural psoriasis.
- In about 7-42percent of patients with psoriasis, there might occur arthritis, called psoriatic arthritis.
- The aim of ultraviolet irradiation is to decrease the rate of DNA synthesis in the cells of the skin and thus slow down their proliferation.
- It must be realized that, the long ultraviolet rays like UVB, UVA are beneficial for the treatment of psoriasis but no UVC.
- The different treatment regimens include:
- The Goeckerman regimen: This consists of the application of coal tar 2-3 times a day with general UVB radiation given once a day, as a suberythemal or E1(MED) dose.
- Leeds or Ingram regimen:
- PUVA (Psoralen ultra-violet A):
B) Acne vulgaris
Ultraviolet radiation is given in E2 doses for acne vulgaris, with the following aim-
- An erythema will bring more blood to the skin and so improve the condition of the skin
- Desquamation will remove comedones and allow free drainage of sebum, thus reducing the number of lesions.
- The UVR will have a sterilizing effect on the skin.
- This patients are benefited by mild doses of UVR.
D) Chronic infection
- Ultraviolet radiation at high doses are helpful for the treatment of chronic infection.
- An E4 dose can use for it.
- One evidence suggests that topical glucocorticoids and psoralen-UVA (PUVA) or narrowband UVB at a wavelength of 311nm are effective for the management of this condition.
F) Treatment of vitamin deficiency
- As already stated, cholecalciferol (vitamin D3) is formed in the skin, by the action of UVB and UVC on 7-dehydrocholesterol.
- Exposure to artificial UVR or artificial sun light is curative for vitamin D deficiencies such as rickets, osteomalacia, and senile osteoporosis.
G) Protection for hypersensitive skin
Person who work outside in the strong sunshine region, can have reduce effects of sun burn .
Suberythemal doses of UVB reducing blood pressure.
Pruritus due to uremia in patient with chronic renal failure also shows result when treated using suberythemal doses of UVB
Contraindications of UVR
- Irradiation of the eyes
- Skin cancer
- Pulmonary tuberculosis
- Cardiac, kidney and liver disease
- Systemic lupus erythematosus
Precautions to the Use of UVR
- With patients taking photosensitizing medication
- Recent Radiotherapy
- Until the effects of the prior dose have disappeared
Dangers of UVR
- Premature skin aging
- Damage to eyes
- Adverse effects due to PUVA
- Electrotherapy Therapy Simplified – Basant Kumar Nanda