Laser Hazards, Safety, and Injuries
Aaron B. Zimmerman
Neal Whittle
Laser light is highly monochromatic, is highly coherent, is highly directional, and has a high-power density. Each of these things makes lasers useful for a variety of applications, including ophthalmic surgery. However, each of these attributes also makes laser light hazardous to the eye. Recognizing these hazards and taking steps to reduce them is vital to ensure the safety of the physician, their staff, and their patients.
TYPES OF HAZARDS
Some powerful lasers can represent a fire hazard, as they can ignite flammable substances. This is especially true for lasers used for thermal purposes. Lasers used for surgical purposes often require large amounts of electricity to operate, and therefore they can pose an electrical hazard. Chemical and biological hazards also exist. The previously mentioned dye lasers have a liquid medium that is highly carcinogenic.1 The tissue plume created by the excimer laser during laser in situ keratomileusis and photorefractive keratectomy can also contain harmful particles such as viruses (including human immunodeficiency virus), bacteria, carcinogens, and other toxic aerosols.2
High-powered lasers can pose skin hazards.1 Depending on the wavelength, the skin can suffer from either a thermal injury or a photochemical injury. Thermal injuries occur when longer wavelength light (low-energy photons) causes a heat-based denaturation of the tissue’s proteins. Photochemical injuries result from shorter wavelengths (high-energy photons) damaging the tissue’s deoxyribonucleic acid (DNA) by introducing free radicals or directly damaging the DNA base pairs. Cell membranes are particularly susceptible to free radicals, so once introduced to a localized tissue, significant damage can occur. Higher-energy light can also directly damage the base pairs on cellular DNA, eventually leading to cellular apoptosis and cell death if the damage is sufficient.
Eyes are particularly prone to laser injuries. Depending on the laser’s wavelength, laser light might be absorbed in the cornea, lens, or retina (Table 5.1).3 Visible wavelengths are particularly hazardous, as they can pass freely through the eye and damage the retina, leading to permanent vision loss. Similar to the skin, the eye is susceptible to thermal and photochemical injuries. Photoreceptors
contain large amounts of cell membrane, and therefore photochemical-free radical damage from visible laser light can quickly cause a retinal injury.
contain large amounts of cell membrane, and therefore photochemical-free radical damage from visible laser light can quickly cause a retinal injury.
TABLE 5-1 A COMPARISON OF OCULAR AND SKIN PATHOLOGICAL EFFECTS FROM DIFFERENT WAVELENGTH BANDS OF LASER LIGHT | ||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||||||||||||||||||||
CATEGORY OF RISK
The degree of hazard does not just depend on the laser’s power but also depends on several other factors that, when combined, determine the type and severity of the damage.1 These factors include the pulse time, the beam size, beam divergence, and wavelength. The beam width and divergence change the power density of the beam. A smaller diameter beam would be more dangerous than a larger beam, as the energy is concentrated in a smaller area. The wavelength of the laser comes into play as well. For example, a person exposed to an infrared (IR) beam would not perceive the beam as visible. The individual would not blink or turn away due to this lack of sensitivity and would be at a greater thermal risk to the eye than a visible beam of equivalent power.
Lasers are grouped into four major categories based on the level of risk they present, particularly to the eye. There are two laser classification systems. The first system was developed in the 1970s and is still used today by the U.S. Food and Drug Administration (FDA). In 2002, the International Electrotechnical Commission (IEC) developed a revised classification system, which has been gradually phased in. The revised system’s main purpose is taking the previous system and adding in the concept of maximum permissible exposure, which is the highest power density of laser light that is considered safe to the eye. Both the old and revised systems are currently accepted by the American National Standards Institute (ANSI) and the FDA. Both systems have four classifications, with the risk increasing with higher classes. Higher-risk lasers may damage the eye within the blink response time (0.25 s)1, while
lower-risk lasers might require significantly more time. The FDA classification system uses Roman numerals (I-IV) while the revised IEC classification uses Arabic numerals (1-4).4 Using the FDA classification system, examples of each laser class are found in the following section (Table 5.2):
lower-risk lasers might require significantly more time. The FDA classification system uses Roman numerals (I-IV) while the revised IEC classification uses Arabic numerals (1-4).4 Using the FDA classification system, examples of each laser class are found in the following section (Table 5.2):
TABLE 5-2 COMPARISON OF FOOD AND DRUG ADMINISTRATION AND INTERNATIONAL ELECTROTECHNICAL COMMISSION CLASSES, LASER HAZARDS, AND CLASS EXAMPLES | ||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||||||||||||||||||
Class I
Class I lasers are unable to emit a hazardous level of light under normal use. Class I laser devices can include lasers that might be classified as more hazardous but are enclosed in a way that they are not for viewing, such as a Blu-ray player or a laser printer.
Class II
Class II lasers are considered to be relatively safe. They are visible wavelength lasers (400-700 nm) that must be less than 1 mW. Any direct exposure shorter than the blink response time (0.25 s) will cause no damage to the retina. To produce retinal damage, the laser must be exposed to the retina for up to 1000 seconds, which is nearly 17 minutes.
Class III (IIIa and IIIb)
Class III lasers are divided into two subcategories, IIIa and IIIb. Class IIIa lasers are visible wavelength lasers of powers between 1 mW and less than 5 mW. They are
considered “safe” when exposure is less than the blink response time but only safe in the sense that they will not cause injury to the retina. They may still cause temporary flash blindness by bleaching the photoreceptors. Most handheld laser pointers fall into this category.
considered “safe” when exposure is less than the blink response time but only safe in the sense that they will not cause injury to the retina. They may still cause temporary flash blindness by bleaching the photoreceptors. Most handheld laser pointers fall into this category.
Class IIIb lasers are visible lasers between 5 mW and 500 mW of power or any ultraviolet and IR laser 500 mW and below. These lasers represent a direct exposure hazard, meaning they can damage the retina within the blink response time if the beam is viewed directly or by specular reflection. Specific controls, such as protective filters, are recommended but not required by the Occupational Safety and Health Administration (OSHA) or the FDA. Some Q-Switched neodymium yttrium aluminum garnet (Nd:YAG) lasers used for capsulotomies and peripheral iridotomies are Class IIIb, but some are class IV.
Class IV
Class IV lasers are the most hazardous lasers in the classification system. They are lasers of any wavelength with a power greater than 500 mW. They can cause injury by direct viewing, specular reflection, and diffuse reflection. Most ophthalmic lasers fall into this category. Eye protection is required when operating class IV lasers.
LASER SAFETY REGULATIONS
There are several regulatory bodies that oversee the use of lasers in various settings, including ophthalmic surgery. In the United States, the development and use of laser safety standards is overseen by ANSI. Laser safety standards fall under ANSI Z136 and have several subcategories depending on what applications the laser will be used in, how to evaluate and protect against laser hazards, and the labeling and testing of protective equipment. The Z136.1 standard specifically covers the general use, hazards, and safety of lasers and serves as the parent document for all other ANSI laser standards. Z136.3 covers safe laser use in all health care fields, including ophthalmic use. It is a comprehensive resource that details laser hazards, non-beam hazards, training, administrative protocols, protective equipment, warning signage, and more. OSHA enforces laser safety standards to ensure employees’ safety and well-being. Laser safety is covered in Section III: Chapter 6 of the OSHA Technical Manual, with specific control measures that are recommended (Class IIIb) or required (Class IV), depending on the class of laser being used.1
There are also regulatory bodies that oversee the manufacture and sale of lasers. The FDA regulates the sale of lasers in the United States, including those used in medical settings. Some lasers are exempt from FDA regulation if they are designed so that they are not for viewing under normal operation (e.g., a laser printer or DVD player). Lasers used for ophthalmic purposes are typically more hazardous. Therefore, they have stricter regulations such as keyed access, protective housings and interlocks,
filters, shutters, a means of measuring laser output, and emergency stops. Each laser used for surgical or therapeutic purposes requires either FDA 510 k clearance or premarket approval.
filters, shutters, a means of measuring laser output, and emergency stops. Each laser used for surgical or therapeutic purposes requires either FDA 510 k clearance or premarket approval.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
