Laser Surgery in Horses

The term "laser" conjures up images varying from action movies to removal of skin wrinkles to hands-free toilet flushing. What these things have in common is that a beam of light with a particular wavelength produces a particular desired effect. A surgical laser simply delivers coherent (meaning the beam stays together indefinitely), monochromatic (single wavelength as opposed to the visible spectrum of many wavelengths) light to produce a specific tissue interaction. All lasers are not the same; that is, each wavelength has its own properties and delivery options and most are not visible. Lasers are generally named according to the material that produces the laser light.

Laser surgery offers the benefits of reduced hemorrhage (bleeding) and postoperative swelling because the heat seals small vessels and lymphatics. Postoperative wounds are also less painful because small nerves are incapacitated. Most importantly, specialized delivery devices allow endoscopic access to surgical sites and facilitate surgery that was previously impossible or only possible with very invasive procedures, such as surgery to remove a tumor in the nasopharynx or to relieve clinical signs for guttural pouch tympany. Laser energy is used to cut, coagulate, or ablate (vaporize) tissue. In this case, coagulation refers to protein; when denatured, protein is replaced by scar tissue or it simply dies and falls away. Ablation is the conversion of tissue to smoke and steam, which is vacuumed away.

The carbon dioxide (CO2) laser is probably the most common instrument in veterinary surgery today. Its wavelength is highly absorbed by water, which is very dense in tissue and makes laser surgery's effect essentially "what you see is what you are getting" (you don't have to worry too much about damaging deeper tissues). This laser must be reflected down an articulated arm with mirrors or highly reflective semi-flexible waveguide to be delivered to tissue. When focused into a small beam, tissue can be incised with almost no collateral (adjacent) tissue heating. Because this laser is insensitive to tissue color and is absorbed by water, it can be used to ablate masses without affecting deeper tissue. A good example is corneal squamous cell carcinoma, a common equine eye tumor. The tumor can be ablated without affecting the deeper corneal stroma or other structures inside the eye.

Either by hand manipulation or using computerized scanning technology, the beam can be moved across a skin tumor, vaporizing thin layers of abnormal tissue while leaving the normal underlying deeper layers of skin. This is the same technology used for human skin resurfacing. Many more applications will become available when the wavelength can be better delivered through a flexible endoscope.

The gallium-aluminum-arsenide diode laser (diode for short) and its similar predecessor, the Nd:YAG laser, can be delivered through a flexible quartz fiber inserted through a video endoscope. This wavelength is minimally absorbed by water, but is highly absorbed by darker pigment such as melanin or hemoglobin. Normal minimally pigmented skin or mucous membranes contain little enough of these pigments to allow penetrations of 5-10 mm below the surface. In some sites, this can be dangerous to deeper structures. The cornea contains no pigment, so it is unaffected by these wavelengths; the energy passes through to allow iris or retinal surgery with no corneal effect at all.

Endoscopic surgery of the equine upper airway has been facilitated tremendously by these lasers. Procedures that previously required general anesthesia and invasive approaches can be performed on an outpatient basis with the horse standing. Common procedures include transection of epiglottic entrapments, debridement of infected laryngeal cartilages, removal of the vocal cords and laryngeal ventricles, incision of the guttural pouch septum to relieve tympany in foals or adults, and vaporization of upper airway tumors or inflammatory masses.

Once the instruments are available, new applications constantly arise. Some newer laser procedures include non-invasive removal of bladder stones from geldings or restoring function to horses lame from distal hock disease through the use of laser energy on the hock joints.

About the Author

Kenneth E. Sullins, DVM, MS, Dipl. ACVS

Kenneth E. Sullins, DVM, MS, Dipl. ACVS, is a professor of Surgery in the Marion duPont Scott Equine Medical Center at Virginia-Maryland Regional College of Veterinary Medicine, Leesburg, Va. He began doing laser surgery in the late 1980s, and is the author of upcoming book Practical Equine Laser Surgery from Mosby/Elsevier Health Sciences.

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