A laser generates a beam of light of a single wavelength where the light waves move in the same direction and are exactly in phase (their peaks and valleys are perfectly aligned). This makes the beam intense and highly directional. These optical properties make lasers useful for many commercial and consumer applications. But they also make lasers potentially dangerous to the user and others nearby.
Most common consumer devices should be reasonably safe for adult use. However, even the safest of devices can cause injury if they are used in ways that were not intended by the manufacturers. For instance, lasers normally considered safe can damage the eyes when viewed with an optical instrument, such as a telescope or microscope. As a general rule, one should never point a laser beam into their eyes regardless of its safety rating. A mistaken assumption about the class of a laser may cause irreversible eye damage.
THE TWO WAYS THAT LASERS DAMAGE EYE TISSUE
All lasers of sufficient power can damage the eyes. However, even low powered lasers can cause injuries when abused. For example, children have been known to continuously stare into consumer-safe laser pointers and have suffered eye injuries as a result. Depending on their wavelength, lasers cause injury by one of two possible mechanisms. These are photochemical effects and thermal effects.
Light can cause a chemical reaction in some substances. The photosynthesis occurring in most green plants when exposed to sunlight is an example of a photochemical effect. The conversion of light into nerve impulses in the eye’s retina is another example. On the other hand, unwanted photochemical effects from intense laser light can damage eye tissue and cause vision problems or blindness.
Light in the infrared range of the spectrum can cause thermal burns. Heat causes all molecules to vibrate. Excessive heat increases this vibration to the point where the chemical bonds of some molecules break apart. In human tissue, this is experienced as a burn. Intense laser light can cause severe thermal burns to the eyes.
3 BASIC TYPES OF LASERS
AND HOW THEY AFFECT THE UNPROTECTED EYE
Laser beams are produced in a number of ways and can be broadly grouped by their wavelengths. The three common types are ultraviolet lasers, visible light lasers, and infrared lasers.
Ultraviolet lasers have many applications in research and manufacturing. Their short wavelengths make them ideal for micro-machining and in making printed circuits. Ultraviolet light is also highly energetic, which makes UV lasers useful for sterilization devices. Ultraviolet light is invisible, which means that eye exposure can happen without the victim’s awareness. Eye damage occurs by photochemical effects, and the speed and severity of an injury will depend on the laser’s power. Where the injury occurs in the eye depends on whether the laser light is UV-A, UV-B, or UV-C.UV-A interacts with both the cornea (the outer transparent layer) and the lens of the eye. Photochemical damage, therefore, occurs to both of these eye structures. Damage to the lens can cause cataracts or blindness. UV-B and UV-C cause photokeratitis to the cornea and to the outer layer covering the white of the eye. Photokeratitis is essentially sunburn, but when caused by intense laser light, the effects are severe.
Visible lasers also have many applications such as in pointers, surveying equipment, barcode scanners, gun scopes, laser light entertainment, and optical alignment equipment. Because this type of laser beam is visible, eye exposure is obvious to the victim. If the laser power is low, the blinking reflex is sufficiently fast to protect the eye.Visible light penetrates through the cornea and is focused by the lens onto the retina at the back of the eye where it is turned into nerve impulses. Visible laser light can cause irreversible photochemical damage to the retina. This damage is made worse by the focusing effect of the eye’s lens, which acts much like a magnifying lens does when it focuses sunlight to a small point that can burn the paper. In this case, the eye’s lens focuses on laser light to a small point on the retina, which intensifies photochemical damage.
Infrared (IR) lasers are used in materials processing, cutting, drilling, welding, polishing, and engraving. Infrared laser beams project intense heat and therefore cause thermal burning to eye tissue. The parts of the eye affected will depend on whether the laser light is IR-A, IR-B, or IR-C. IR-A penetrates to and interacts with the retina. That is, the cornea and lens are transparent to IR-A, while the retina absorbs and is burned by it.The more powerful the laser and the longer the exposure, the more severe the burning. Like ultraviolet light, infrared is invisible and, therefore, the victim has no awareness of laser exposure until after the damage occurs. IR-B and IR-C are absorbed by and burn the cornea.
WHEN TO WEAR LASER SAFETY GLASSES
Know the class, power, and wavelength of the lasers you use. These are important because, without them, you won’t know whether eye protection is needed, and if it is, you won’t know the type of eye protection required. Wear laser safety glasses for class 3R, 3B, and class 4 lasers. Note that reflected laser light can also cause eye damage. With class 4 lasers, even diffuse reflections can cause injury.Your choice of laser safety glasses will also depend on the laser’s power and wavelength. For some lasers, even a chance split-second reflection off a mirror or other reflective surface is enough to cause severe injury or blindness. Always wear your safety glasses. For more information, don’t hesitate to contact us.