This document provides an overview of low intensity laser therapy. It defines lasers and describes their production process, involving a lasing medium, power supply, and resonating cavity. Lasers produce beams that are monochromatic, coherent, and collimated. They are classified based on potential biological hazards and energy output. Laser-tissue interaction depends on wavelength, incidence angle, and tissue type. Mechanisms of low-level laser therapy involve cellular chromophores absorbing photons and initiating photochemical reactions.

1. Low Intensity Laser
Therapy
Presented by
Dr. Doaa Rafat
Lecturer at Basic Science Department

2. Low Intensity Laser Therapy
Students learning objectives
Define LASER.
Describe the mechanisms of LASER production.
Explain the characteristics of LASER beam.
Identify the different types of LASER.
Explain physiological effects of LASER.
Describe indication, contraindication and precautions of LASER
therapy.

3. Definitions:
Light is a form of electromagnetic waves with wavelength (100 – 10,000 nm)
It contains tiny "energy packets" called photons.
Photons are "energy packets" that contain certain amount of energy according to
its wavelength.
The word LASER is an acronym for Light Amplification by Stimulated
Emission of Radiation.
The word LASER refers to:
Light: Electromagnetic radiation that can produce visual sensation.
Amplify: To increase in size, volume or significance.
Stimulate: To excite, encourage or provoke something to grow, develop or
become more active.

4. • Emission: A flowing forth, such as the release of electrons from
parent atoms.
• Radiation: The transfer of energy in the form of rays, waves or
particles, often from a central source; also called radiant energy.
• LASER is an amplified type of light beam that is different from
ordinary light beam, with very specific wavelength and therefor
specific energy.
• Electromagnetic waves consist of electrical and magnetic fields
perpendicular to the direction of propagation and to each other with
fluctuating amplitude.

5. LASER production
LASER production requires the followings;
A- Lasing medium (gain medium):
• It is a material that generates the LASER light.
• It can include any types of matters; gas, solid or liquid.
• This material is capable of absorbing energy and subsequently
gives off excess energy as photons of specific wave length.
B- Power supply to excite lasing medium:
• LASERs use an electrical power supply that can potentially
deliver up to 10,000 V.

6. C- Resonating cavity
It is a mirrored chamber that contains the lasing medium.
The two mirrors are placed on both ends of the lasing
chamber.
One mirror is totally reflective and reflects all beams falling
on its surface.
The other mirror is semipermeable (partially reflective) and
wavelength matched that permits beams with one wavelength
only to pass.

7. D- Steps for LASER production;
• Excitation:
• Atoms become excited by application of an external power
energy.
• Incident photons are absorbed by resting electrons of the
lasing media which move it to higher energy level.
• Spontaneous emission:
• Excited electron drops to lower resting level emitting single
photon of a specific wavelength depending on elements of
the lasing medium.
• Stimulated emission:
• Incident photon interacts with already excited atoms in the
medium to produce two identical photons.

8. The photons are reflected several times within the chamber, which
amplifies the light and stimulates the emission of other photons from
excited atoms.
• Eventually, so many photons are released that the chamber cannot
contain the energy.
• As photon concentration increases, the photons are emitted through
the partially reflective mirror of the chamber.
• Not all photons are emitted through the partially reflective mirror.
• When a specific level of energy is attained, photons of a particular
wavelength are emitted through the semipermeable mirror.
• The emitted photons constitute the LASER beam.

10. Properties of LASER light
The LASER light is emitted in an organized manner rather than in a
random pattern as from a light bulb. Three properties distinguish the
LASER from incandescent and fluorescent light sources:
Monochromaticity, Coherence and Collimation.

11. 1- Monochromatic:
Monochromaticity refers to a pure spectral color of a single
wavelength. A beam is more and more monochromatic if the line
spread in frequency is narrow or small. The line width in a laser is
generally very small as compared to the normal lights.

12. 2- Coherent:
Coherence means that all the waves of the
emitted light have the same wavelength and
they are all in phase with one another.
On the other hand, in ordinary light, the
waves have different wavelengths and their
phases are superimposed on one another.

13. 3- Collimated:
LASER beam collimation means that there is
minimal divergence of the photons.
That means the photons move in a parallel
fashion and concentrates the beam of light.
On the other hand, the waves of ordinary
light scatter in all directions.

14. 4- Non-divergent:
Non-divergent means that the waves are
incapable of separating or widening.
The light emitted from a LASER pointer is
non-divergent, while the light emitted from a
flashlight is divergent. Non divergent light is
also known as directional light.

15. Classification of LASERs
1- Classification according to potential biological hazards:
FDA classified LASERs depending on potential biological hazardous effect
into four classes.
Potential biological hazards are measured in the blink reflex time (it is a
reflex to protect eye from bright light or foreign body it occurs at rate 0.01
sec).
For all LASER classes, risks and hazards increase if the LASER beam is
viewed with visual aids, e.g., magnifiers, telescopes and binoculars.

16. Class Power Hazards Usage
Class I Low
< 0.5 mW
None on eyes or skin. LASER printers,
blackboard pointer and
CD players.
Class II Low
Up to 1mW
Safe on skin.
Eye protected by aversion response.
Barcode scanners.
Class III III a (3R):
Low–up to 5
mW.
Might be momentarily hazardous when
directly viewed or when staring at the
beam without goggles.
Some therapeutic
Physical Therapy
LASERs.
III b (3B):
medium – 5
mw-500 mW
Immediate eyes and skin hazard with
direct exposure.
Some therapeutic
Physical Therapy
LASERs.
Class IV High
> 500 mW
Very hazardous to skin and eye from
both direct and reflected beams.
Destructive surgical
models.

17. 2- Classification according to its energy output:
LASERs are also classified into low and high power LASERS
depending on the energy output they emit.
A- High-power LASERs:
Also known as "hot" LASERs due to the thermal responses they
generate.
These are used in the medical field in numerous areas, including
surgical cutting and coagulation, ophthalmologic, dermatologic,
oncologic and vascular specialties.

18. B- Low-power LASERs:
Also known as “cold” LASER.
They produce a maximal output of less than 1 milliwatt (1mW=
1/1000 W).
It acts through producing photochemical effects, rather than thermal
effects.
No tissue warming occurs.
The two types of low power LASERs used by therapist are Helium-
Neon LASER (He-Ne) and Gallium-Arsenide LASER (Ga-As).

19. • The He-Ne gas LASER uses a gas mixture of primarily Helium with
Neon in a pressurized tube. This creates a LASER in the red portion
of the electromagnetic spectrum with a wavelength of 632.8 nm and
direct depth of penetration to 2-5 mm, although there may be some
indirect effects up to 8 to 10mm.
• The Ga-As LASERs utilize a diode to produce an infrared
(invisible) LASER at a wavelength of 904 nm that is directly
absorbed in tissues at depths of 1-2 cm and has an indirect effect up
to 5 cm.

20. LASER-Tissue Interaction:
1. As an electromagnetic radiation, when LASER radiations interact
with any matter, they may undergo reflection, refraction and/or
absorption and hence scattering.
2. When LASER passes into biological tissues, collimation and
coherence properties are diminished or lost.
3. The extent to which this happens depends on the nature and density
of the matter present so that LASER radiations will pass unaffected
through space and be only slightly altered in air (for visible radiations),
but be markedly altered on entering a more dense material such as
biological tissues.

21. 4- Penetration depth of LASER through the tissues depends on:
A- Wavelength and/or frequency of LASER beam:
It is the most important factor affecting LASER absorption and
penetration.
B- Angle of incidence.
C- The type of tissue the light pass through. This determines;
Absorption coefficient which depends on the type and quantity of
chromophores present in the tissue.

22. üChromophores are biomolecules including melanin and
haemoglobin.
üThey absorb optical radiations and can be excited by the incident
photons through its electronic or atomic configuration.
üTheir composition, which is different depending on the tissue type,
determines the response of the tissue itself to the LASER radiation
at a certain wavelength.
üEach type of chromophore absorbs only some specific wavelengths
and let the others pass.

23. D- Absorption of LASER waves is the most important factor
affecting photobiological effects of LASER therapy, so, without
absorption no photobiological and/or clinical effects will occur.
vLASER light with wavelengths between 600 and 1300 nm have
optimum penetration depth in human tissues of 1 to 4 mm and is
therefore most commonly used in the clinical setting.
vLASER light with longer wavelengths, e.g., IR LASER produced by
the Ga-As LASER, penetrates deeper, i.e., 2-5 cm.
vLASER light with shorter wavelengths, e.g., red light produced by
the He-Ne LASER, penetrates less deeply, i.e., 1-2 mm.

24. E- Although all frequencies of LASER penetrate only few millimeters,
deeper physiological effects are thought to occur because the LASER
energy may promote photochemical reactions that mediate processes
distant from the site of application.

25. Mechanisms of Low Level Laser Therapy.
1.Cellular Chromophores and First Law of Photobiology
The first law of photobiology states that for low power visible light to
have any effect on a living biological system, the photons must be
absorbed by electronic absorption bands belonging to some molecular
photoacceptors, or chromophores.
A chromophore is a molecule (or part of a molecule) which imparts
some decided color to the compound of which it is an ingredient.
Chromophores almost always occur in one of two forms: conjugated pi
electron systems and metal complexes.

26. Examples of such chromophores can be seen in chlorophyll (used by
plants for photosynthesis), hemoglobin, cytochrome c oxidase (Cox),
myoglobin, flavins, flavoproteins and porphyrins.

27. 2. Action Spectrum and Tissue Optics
One important consideration should involve the optical properties of
tissue. There is a so-called “optical window” in tissue, it is the range
of wavelength where light has its maximum depth of penetration
in tissue. This optical window runs approximately from 650 nm to
1200 nm.

28. The absorption and scattering of light in tissue are both much higher
in the blue region of the spectrum than the red.
Because the principle tissue chromophores (hemoglobin and
melanin) have high absorption bands at shorter wavelengths, tissue
scattering of light is higher at shorter wavelengths, Therefore the use
of LLLT in animals and patients almost exclusively involves red and
near-infrared light (600-1100-nm).

29. 3. Mitochondrial Respiration and ATP
Mitochondria play an important role in energy generation and
metabolism. Mitochondria are sometimes described as “cellular power
plants”, because they convert food molecules into energy in the form
of ATP via the process of oxidative phosphorylation.
The mechanism of LLLT at the cellular level has been attributed to the
absorption of monochromatic visible and NIR radiation by
components of the cellular respiratory chain. Several pieces of
evidence suggest that mitochondria are responsible for the cellular
response to red visible and NIR light.

30. The effects of He Ne laser and other illumination on mitochondria
isolated from rat liver have included increased proton electrochemical
potential, more ATP synthesis, increased RNA and protein synthesis and
increases in oxygen consumption, membrane potential, and enhanced
synthesis of NADH and ATP.
(NADH) is nicotinamide adenine dinucleotide (NAD) + hydrogen (H)."
This chemical occurs naturally in the body and plays a role in the
chemical process that generates energy.

31. 4. Cytochrome c oxidase and nitric oxide release
Cox is the primary photo acceptor for the red-NIR range in mammalian
cells. Nitric oxide produced in the mitochondria can inhibit respiration
by binding to Cox and competitively displacing oxygen, especially in
stressed or hypoxic cells.
Increased nitric oxide (NO) concentrations can sometimes be measured
in cell culture or in animals after LLLT due to its photo release from
the mitochondria and Cox. It has been proposed that LLLT might work
by photo dissociating NO from Cox, thereby reversing the
mitochondrial inhibition of respiration due to excessive NO binding.

32. 5. Reactive oxygen species and gene transcription
Reactive oxygen species (ROS) and reactive nitrogen species (RNS)
are involved in the signaling pathways from mitochondria to nuclei.
Reactive oxygen species (ROS) are very small molecules that include
oxygen ions such as superoxide, free radicals such as hydroxyl radical,
and hydrogen peroxide, and organic peroxides.

33. They are highly with biological molecules such as proteins, nucleic
acids and unsaturated lipids. ROS form as a natural by-product of the
normal metabolism of oxygen and have important roles in cell
signaling, regulating nucleic acid synthesis, protein synthesis, enzyme
activation and cell cycle progression. LLLT was reported to produce a
shift in overall cell redox potential in the direction of greater oxidation
and increased ROS generation and cell redox activity have been
demonstrated

34. These cytosolic responses may in turn induce transcriptional changes.
Several transcription factors are regulated by changes in cellular
redox state. But the most important one is nuclear factor B (NF-B).
ATP synthesis activated after LLLT and it is instrumental in causing
transcription of protective and stimulatory gene products.

35. 6. Downstream cellular response
LLLT can prevent cell apoptosis and improve cell proliferation;
migration and adhesion at low levels of red/NIR light illumination.
LLLT at low doses has been shown to enhance cell proliferation in
vitro in several types of cells: fibroblasts keratinocytes, endothelial
cells, and lymphocytes.
The mechanism of proliferation was proposed to involve photo
stimulatory effects in mitochondria processes, which enhanced growth
factor release, and ultimately led to cell proliferation, the attachment
and proliferation of human gingival fibroblasts were enhanced by
LLLT in a dose-dependent manner.

36. LLLT modulated matrix metalloproteinase activity and gene
expression in aortic smooth muscle cells. LLLT could activate skeletal
muscle satellite cells, enhancing their proliferation, inhibiting
differentiation and regulating protein synthesis.
(Satellite cells are the primary stem
cells in adult skeletal muscle and
are responsible for postnatal muscle
growth, hypertrophy and
regeneration.)

37. Physiological Effect of LASER:
1- Physiological effects of LASER occur at cellular level.
2- It is produced by interaction of photons with biological tissues
which is called bio-stimulation or Photo biostimulation.
3- Bio-stimulation acts through;
• Alteration of cell membrane potentials.
• Improving nuclear activity.
• Increasing cell metabolism.
• Increasing cell proliferation.
• Increasing cell motility.

38. 4- There are two major effects of LASER;
• Tissue healing
• Pain control.

39. Therapeutic effects of LASER therapy:
1- Facilitation of wound and fracture healing:
A- LASER therapy promotes healing of chronic and acute wounds
such as surgical wounds, ulcers, bed sores and burn through;
1. Enhancing cellular metabolism and ATP production.
2. Increasing collagen synthesis and procollagen RNA levels.
3. Increasing tensile strength of the wound.
4. Stimulation of angiogenesis (development of new blood vessels).
5. Improving circulation and inhibiting bacterial growth.
6. Stimulating Leukocytic, phagocytosis and fibroblast proliferation.

40. B- In case of bone healing, LASER therapy enhances the
following;
1. The rate of hematoma absorption.
2. Bone remodeling (new bone formation).
3. Blood vessel formation and calcium deposition.
4. Fibroblast and chondrocyte activity.

41. 2- Pain control:
LASER therapy reduces acute and chronic pain e.g., musculoskeletal
pain, post-surgical pain and neuropathic pain through its analgesic,
myorelaxant, tissue healing and bio-stimulation effects. The analgesic
effects of LASER occur through;
1. Increasing endogenous opiates production.
(Endogenous opiates are enkephalins and endorphins that are
primarily produced in the brain)

42. 2. Increasing local release of neurotransmitters such as serotonin.
3. Decreasing conduction velocity of pain fibers.
4. Indirect effect through hastened healing and anti-inflammatory
effects.
5. Reducing interstitial swelling by stimulating the activity of
lymphatic system.

43. 3- Nerve conduction and nerve regeneration:
LASER increases nerve conduction velocities, decreases distal sensory
latencies and accelerates nerve regeneration, which indicates increased
activation of the nervous tissue.
4- Immunologic response:
LASER therapy stimulates the immune system through;
1. Activation of phagocytes.
2. Stimulation of macrophages.
3. Stimulation of mast cell degranulation.

44. 5- Anti-inflammatory and anti-edematous effects:
LASER enhances anti-inflammatory and anti-edematous effects
through;
1. Enhancing natural defense mechanism through stimulating
phagocytosis with a destructive effect on the irritant products.
2. Decreasing the level of prostaglandin (PGE2) which promotes
reduction of edema and washes out pro-inflammatory
molecules.

45. 6- Anti-edema effects:
LASER decreases edema through;
1. Increasing the diameter of lymphatic vessels electively, which
increase the removal of edema.
2. Dilating and modulating the permeability of lymphatic
capillaries and vessels to increase reabsorption of edema.

46. 7- Improvement Circulation:
LASER irradiation improves microcirculation in the area of
application

47. Indications of LASER therapy:
1. Non- infected and infected skin wound and ulcers.
2. Non-united fracture.
3. Acute and chronic musculoskeletal inflammations, e.g.,
osteoarthritis and rheumatoid arthritis.

48. 4. Acute and chronic soft tissues injuries, e.g., tendon, ligaments,
muscle and nerve injuries.
5. Neuropathic pain, e.g., trigeminal neuralgia, post-herpetic
neuralgia and carpal tunnel syndrome.
6. Trigger point and acupuncture point stimulation.
7. Lymphedema.
8. Pain management.

49. Contraindication of LASER therapy:
1. Ischemia and poor circulation.
2. Cancerous tumors: LASERs deliver nonionizing radiations,
therefore; It doesn’t produce any damage to DNA and/or cell
membranes. It doesn’t produce carcinogenic effects unless applied
to already cancerous cells, but tumorous cells may proliferate
when stimulated.
3. Direct eye exposure.

50. 4. Pregnancy.
5. Hemorrhagic regions.
6. Gonads.
7. Over the thyroid or other endocrine glands.
8. Within 4 to 6 months after radiotherapy.

51. Precaution of LASER therapy:
1. Epilepsy.
2. Fever.
3. Impaired mentality or unreliable patient.
4. Areas of decreased sensation.

52. 5. Epiphyseal plates of children.
6. Sympathetic ganglia.
7. Vagus nerve.
8. Photophobia or abnormally high sensitivity to light.
9. Patients treated with photosensitizers.
10.The therapist and patient should use protective goggles.