FAQ - Medical Applications

Presently lasers are being widely used for numerous medical applications. These include surgery, ophthalmology, dermatology, angioplasty, cancer treatment, urology, and cosmetic applications such as laser hair removal, tattoo removal and liposuction, Low Level Laser Therapy (LLTP) etc.

Laser light interacts with the tissue and transfers the energy of photons to tissues because of absorption. Laser heating of tissues above 50°C but below 100°C induces disordering of proteins and other bio-molecules. This process is known as photocoagulation. When lasers are used for photocoagulation during surgery, the tissues shrink in mass because water is expelled at these temperatures. The heated region changes its colour and loses its mechanical integrity. Cells in the photocoagulated region die and the tissue is a dead one and can be pulled or removed. The process of laser-induced photocoagulation can be used to destroy tumors, to treat various eye conditions like retinal disorders caused by diabetes, bloodless incision or excision in laser surgery. When very high laser power densities are used, lasers quickly heats the tissues beyond 100°C resulting in boiling and evaporation of water in the tissues. Since 70% of the body tissue is water, the boiling change the tissue into a gas. This phenomenon is called photo-vaporization. Photo - vaporization results in complete removal of the tissue thus making the process suitable for skin rejuvenation, resurfacing and of course bloodless incision or excision in laser surgery. For Photo - vaporization, the tissues must be heated quickly to more than 100°C thus requiring high power density in a pulsed mode. In general power density upto 10W/cm² results in heating of tissues, whereas laser power in the range of 10 - 100W/cm² results in photocoagulation. Power density greater than 100W/cm² is required for photo - vaporization. It is worth mentioning that a given laser can be used for photo-vaporization in the focused mode, whereas same laser can also be used for photocoagulation in the defocused mode. High power lasers like excimer lasers in the ultraviolet range, can break the chemical bonds without even heating the tissues locally thus resulting in photochemical ablation. The photochemical ablation results in clean-cut incision. The thermal component is relatively small and the zone of thermal interaction is limited in the incision wall.

Glaucoma, Cataract, Diabetic retinopathy and Photorefractive keratectomy (PRK) and Laser-Assisted -in- situ Keratectomy (LASIK)

Laser-tissue interactions in ophthalmology can occur in several ways, depending on the power, pulse-duration and wavelength. These interactions can have photothermal, photochemical and photoionizing effects.

Nowadays, a number of lasers are used in dermatological applications. They are argon laser (488nm & 514nm), tunable dye lasers (585 to595nm), doubled Nd:YAG (532nm), krypton laser (568nm), alexandrite laser (755nm), Nd:YAG (1064nm), Er:YAG (2940nm), CO₂ laser (10600nm) etc. The pulse width of these laser systems vary from milliseconds to nanoseconds (pulsed) or the laser may be of continuous nature (CW).

It would be not out of place to mention that there are certain adverse effects of laser treatments, as these are basically burns. These include:

• Pain, bruises, blisters, redness may occur as temporary effects
• Possibility of infection
• Permanent pigment changes
• Rare occurrence of scarring

Three types of lasers are being used in these procedures: the carbon dioxide (CO₂), the holmium:yttrium-argon-garnet (Ho:YAG), and the excimer lasers. Of these, the Food and Drug Administration (FDA) has approved only the CO₂ and Ho:YAG lasers for use in TMR. CO₂ (10.6 micron) and the Ho:YAG ( 2.1 micron) lasers rely on thermal energy to create channels, whereas the excimer laser (308 nm) ablates tissue by dissociating molecular bonds. The CO₂ laser is transmitted through a series of mirrors and lenses. Whereas, the Ho:YAG and the excimer lasers allow the laser beam to be transmitted by an optical fiber. Usually high-energy pulses of 40 - 60 J with pulse width of few tens of milliseconds of CO₂ lasers are required for these procedures. Ho:YAG lasers used for these applications are generally with a peak power of around 10W and pulse width of 200 - 400 microseconds. Excimer lasers employed for these applications are usually 30 - 100 nanosecond pulses with energies in the range of few tens of milijoules per pulse.

Lasers have been in use in dentistry for the last more than two decades. These are being used to treat various problems such as Tooth decay, gum disease, biopsy or lesion removal and teeth whitening etc.

Lasers can be used either to shrink or destroy a tumor with heat or to activate a chemical - known as a photosensitizing agent - that kills only the cancer cells. This process is generally known as photodynamic therapy or PDT. The CO₂, argon, Ho:YAG and Nd:YAG lasers are used to shrink or destroy tumors.

Low-level laser therapy affects cellular activity in many ways such as stimulating cell growth; increasing cell metabolism; improving cell regeneration; producing an anti-inflammatory response; producing an edema reduction; reducing fibrous tissue formation; stimulating nerve function. There are no known permanent or serious side effects from appropriately applied laser therapy.

LLLT uses low-powered laser light in the range of 1-1000 mW, at wavelengths from 632-1064 nm helps in Neurorehabilitation by stimulating a biological response. These lasers emit no heat, sound, or vibration. Instead of generating a thermal effect, LLLT acts by inducing a photochemical reaction in the cell, a process referred to as biostimulation or photobiomodulation.