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 Encyclopedia - Lasers

What are lasers?
What are the types of lasers and their uses?

What are lasers?

The word "laser" is an acronym for light amplification by stimulated emission of radiation. In most lasers used in ophthalmology, an electric current is passed through a tube that contains an amplifying medium, usually a gas or solid material, which serves to intensify the energy. This energy is emitted as a narrow light beam which, when focused through a microscope, will either cut, burn, or dissolve various tissues.

Different types of lasers emit specific colors of light and are used to treat various eye problems. The lasers are usually named for the amplification materials used. For instance, the carbon dioxide laser is called a CO2 laser, while the YAG laser contains a solid material made up of yttrium, aluminum, and garnet.

Ophthalmic lasers allow precise treatment of a variety of eye problems without risk of infection. Most laser procedures are also relatively painless and can be done on an outpatient basis. This combination of safety, precision, convenience, and reduced cost make lasers one of the most successful medical tools available to physicians.

What are the types of lasers and their uses?

Excimer laser
The Excimer laser is perhaps the best known of all lasers because of its use in laser vision correction surgery such as laser in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). The Excimer, or pulsed gas laser, emits an ultraviolet light beam, vaporizing tissue by breaking down molecular tissue bonds in a minute targeted area. It is called a cold laser because it doesn't produce heat that could have harmful effects to the surrounding tissue.

The Excimer laser is precise. Each pulse of the laser removes about 1/500 of the thickness of a human hair. Its precise depth and area control are significant in surgical applications such as refractive vision correction.

YAG laser
An acronym for yttrium-aluminum-garnet, the YAG laser produces short-pulsed, high-energy light beams to cut, perforate, or fragment tissue. This laser may also be called a neodymium-YAG or ND-YAG laser.

Cataract patients often have the misconception that a YAG laser is used to remove their cataracts, but no lasers are used in cataract surgery. This misconception occurs because up to 75 percent of cataract patients develop a condition known as posterior capsular opacification, a clouding of the residual lens capsule left in place after cataract surgery. This gradual loss of vision resembles the symptoms of cataract development, making some people believe that their cataracts have grown back.

The YAG laser is commonly used to vaporize a portion of the capsule, allowing light to pass through to the retina. The procedure is completely painless, takes only a few minutes in the office, and is effective in eliminating the cloudy condition.

Holmium laser
Also known as the infrared holmium YAG laser, this laser is used in a refractive surgery procedure called laser thermal keratoplasty (LTK) to correct mild to moderate cases of farsightedness and some cases of astigmatism. Unlike the Excimer laser, which reshapes the cornea by removing or ablating tissue, the Holmium laser produces infrared light that reshapes the cornea by causing tissue to constrict. The pulsations from the Holmium laser are computer-controlled to produce a pattern of 8 to 16 tiny beams in concentric rings around the periphery of the cornea. The heated fluid in the spots where these beams hit the cornea creates a series of tiny craters. The subsequent shrinkage pulls in the periphery of the cornea, causing the center to bulge, much like tightening a belt, and thus correcting farsightedness.

CO2 laser
The CO2 laser is a specialized laser that is filled with carbon dioxide gas and uses an infrared emission for cutting tissue through heat absorption. It is one of the most common lasers used in surgery and is good for precise cutting and vaporization of tissue, such as that needed in the treatment of superficial lesions or removing small volumes of tissue.

The CO2 laser is used by ophthalmic plastic surgeons to remove fine wrinkles from around the eyes. This laser precisely removes the outermost layer of skin and the underlying dermis, allowing the regrowth of wrinkle-free new skin.

Erbium laser
The Erbium laser, or erbium-YAG laser, is also used in skin resurfacing and is considered to be more precise and accurate than the CO2 laser. It is able to remove finer wrinkles with less damage to the skin. The depth of penetration is about 5 microns compared with the 20 microns typical of the CO2 laser. The Erbium laser also causes less irregular skin pigmentation in darker skinned individuals, because it produces a thinner laser area and less heat. Because the Erbium laser produces minimal thermal scatter, the healing time is less than the healing time with the CO2 laser.

The Erbium laser is also being used in a promising new clinical procedure to emulsify the eye's natural lens during cataract surgery. Most cataract surgeons currently use a piece of equipment called a phacoemulsifier to break up and remove the cloudy lens. The Erbium laser was chosen for the new technique because of its high absorption rate in water, a primary component of the eye's natural crystalline lens.

Argon laser
The argon laser is filled with argon gas that produces blue/green wavelengths. These particular wavelengths are absorbed by the cells that lie under the retina and by the red hemoglobin in blood, but the blue-green wavelengths can pass through the fluid inside the eye without damage. For this reason, the argon laser is used extensively in the treatment of diabetic retinopathy, a severe disorder of the retina that causes blood vessels to leak. The argon laser can burn and seal these blood vessels.

Retinal detachment is another serious eye problem that can be treated by the argon laser. The laser is used to weld the detached retina to the underlying choroid layer of the eye.

Several forms of glaucoma, which is a leading cause of blindness, are also treated with argon lasers. The very serious angle closure glaucoma, for instance, is sometimes treated by using the laser to create a tiny opening in the iris, allowing excess fluid inside the eye to drain to reduce pressure.

Macular degeneration, a severe condition that affects central vision in older adults, is sometimes treated with an argon or krypton laser. In this treatment, the laser is used to destroy abnormal blood vessels so that hemorrhage or scarring will not damage central vision.

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