Laser eye protectors provide the principal means to assure against ocular injury from the direct or reflected laser beams in the operating room [1,30,31]. Although viewing optics in some surgical specialties may inherently protect the eyes of the laser operator, there are seldom viewing optics in cosmetic applications. If viewing optics are employed during the procedure, their safety with the particular laser should always be ascertained from the manufacturer of the viewing optics. In this regard, ordinary optical glass in compound-lens systems protects substantially against all wavelengths shorter than about 300 nm and greater than approximately 2700 nm [15], although certainly at wavelengths greater than 4000 nm. Laser protective filters may be obtained for endoscopes and other viewing optics for the spectral region between these two spectral bands. Eye protectors are available as spectacles, wrap-around lenses, goggles, and related forms of eyewear. It is important that the eyewear be marked with the wavelengths and optical densities provided at those wavelengths. The markings must be clearly understood by all the operating-room staff. The proper use of eyewear and the meaning of the eye-protector markings are key subjects for laser – safety training of the staff [30-32].
Clear plastic goggles or spectacles with side shields, which are known to be made of polycarbonate, are normally suitable for use with the CO2 laser, but should be marked by the laser-safety officer with an indication of the optical density, for example, “OD-4 at CO2 wavelength of 10.6 pm”. Some Laser Safety Officers (LSOs) may be uneasy about marking eye protectors not sold as “laser” eye protection, because of perceived (or very real) legal concerns. Studies of plastic eye protectors show clearly that polycarbonate is far superior in burn-through resistance than other plastics, and such a marking has been argued to be quite justifiable for use with CO2 lasers having a power output up to about 100 W [29]. In some countries, the marking of eye protection by anyone other than the manufacturer is not legally recognized, and the LSO has no alternative but to obtain similar polycarbonate eye protectors that have been certified and labeled by the manufacturer. Some manufacturers of laser eye protection and some laser-safety specialists have made a major issue of the importance of damage resistance of eye protectors, and this concern is evident in eye-protection standards in Europe. However, burn-through times of plastic eye protectors appear to be of little concern in some quarters, as in the United States [1]. Those who are skeptical about
these concerns of burn-through argue that with the powers generally used in laser surgery of 100 W or less, burn-through is unrealistic, since the wearer would certainly move their head within a second after detecting a flame shooting from the goggle. Indeed, the skin will incur a serious burn as would the unprotected, exposed cornea, and clothing would ignite at levels below plastic burn-through irradiances (Fig. 24.6). Goggles manufactured of special glass can frequently be designed to withstand irradiances higher than the ~ 100 W/cm2 order-of-magnitude typically required to burn through polycarbonate lenses in 10 s [29]. In any case, the eye protector requirements vary from country to country, and the user is under an obligation to be informed of the legal requirements in his or her locality.
Eye protectors have been developed for use with IPL units, more to provide comfort than to merely afford protection. Because of the repeated bright light remitted from the skin or from the side of the applicator, many complain of discomfort and headaches created by looking at the repeated flashing visible light. To avoid this discomfort from repeated transient adaptation of the eyes, some manufacturers offer autodarkening lenses (such as those used in some welding helmets) that automatically become darker during the flash.
A more serious problem associated with laser eye protection occurs when more than one laser eye protector must be worn for some procedures, as in tattoo removal. Several different visible wavelengths may be required to remove the different tattoo inks, and choosing the wrong eye protector during a procedure nearing the end of a tiring day has reportedly injured some dermatologists. Unclear labeling has been one contributing factor. Again, the application of a customized label related to the specific laser has been recommended in
Figure 24.6 The thresholds for corneal and skin damage are of the order of 10 W/cm2 for a 1-second laser exposure. Thresholds for 2-10.6 pm are shown (plot courtesy of B. Stuck, USAMRD, San Antonio, TX). The
some countries (as in the United States). However, in other countries, placing labels not provided by the manufacturer on eye protector may not be approved. To compound the problem, the issue of laser eye protectors having only a coded indication of the protection (e. g., “L4-1064”) is strictly forbidden in the United States, because of the great importance placed upon informing the user in an understandable statement! Hopefully, future safety standards would be harmonized on this subject.
With a constant evolution in skin phototreatment technologies, more attention has been paid to engineering controls incorporated into the laser or lamp product itself [10]. Contact sensors that prevent firing of the device unless within contact with the skin have evolved with ever-increasing reliability. Reliability becomes essential for any products intended for home use, as in laser hair-removal products. The difficulty of determining eye safety and the NHZ is confounded by increased sophistication and complexity of modern phototreatment devices, such as devices with intentionally nonuniform output distribution of optical energy, such as fractionated beams, diode arrays, and some IPL systems. In addition, the safety levels often have to be assessed under two distinct sets of conditions: diffusely reflected light present during normal operation of the device, and direct viewing of the output surface that constitutes a misuse or abnormal condition.