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The safety and efficacy of contact lens wear in the industrial and chemical workplace
Optometry (2007) 78, 596-604
The safety and efficacy of contact lens wear in the industrial and chemical workplace Keith Tyhurst, O.D.,a Ryan McNett, O.D.,b and Edward Bennett, O.D.c a
Marion Eye Centers & Optical, Marion, Illinois; bRyan M. McNett, O.D., L.L.C., Wichita, Kansas; and cUniversity of Missouri College of Optometry, St. Louis, Missouri. KEYWORDS Contact lenses; Industrial safety; Workplace safety; Chemical safety; Contact lens injury; Ocular injury; Personal protective equipment
Abstract BACKGROUND: The use and safety of contact lenses in the industrial and chemical workplace has often been questioned since the 1960s because of many unconfirmed reports of ocular injury resulting from contact lens wear. Because of these urban legends, contact lens wear has been banned or wearers have been required to wear additional personal protective equipment (PPE) not required of non-contact lens wearers. METHODS: Literature review via Medline and Google search. RESULTS: Research has shown that contact lenses typically provide protective benefits that decrease the severity of ocular injury and improve worker performance. While contact lens wear contraindications do exist, in most cases, and with proper precautions, contact lens wear is still possible. CONCLUSIONS: Industrial and chemical companies need to establish written contact lens use policies based on current studies that have shown the safety of workplace contact lens wear when combined with the same PPE required of non-contact lens wearers. Practitioners need to discuss, with their contact lens patients, the additional responsibilities required to maintain proper lens hygiene and proper PPE in the workplace. Optometry 2007;78:596-604
protective benefits against a wide range of environmental workplace hazards when combined with that job’s standard PPE requirements.2 Additionally, contact lenses provide workers with many other visual benefits that allow the wearers to function more efficiently in the workplace than spectacle wearers. Although some environmental or workplace conditions limit or contraindicate contact lens wear, contact lenses have been shown consistently to supplement worker eye protection and provide visual benefits that improve worker performance and job satisfaction.4-6
For the last 40 years, the safety and benefits of contact lens use in industrial and chemical workplaces often has been questioned, causing employers and safety officers to view contact lenses with apprehension.1,2 Numerous popular industrial horror stories have linked contact lens usage with severe ocular injuries, and the negative effects of these legends on company safety policies has caused contact lens wearers to be discriminated against by their employers, who have either banned contact lens wear completely or forced wearers to use extra personal protective equipment (PPE) that is not required of non– contact lens wearers.1,3,4 These additional PPE requirements have been consistently and conclusively shown to be unnecessary by research that reveals that, in most cases, contact lenses provide ocular
Famous contact lens myths
Corresponding author: Keith Tyhurst, O.D., Marion Eye Centers & Optical, 1200 W. DeYoung, Marion, Illinois 62959. E-mail: [email protected]
The most famous industrial contact lens myth originated from an undocumented 1967 incident.7 Supposedly, an arc welder who was wearing soft contact lenses underneath his welding faceshield connected to a 440-volt power line,
1529-1839/07/$ -see front matter © 2007 American Optometric Association. All rights reserved. doi:10.1016/j.optm.2007.02.021
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shorting out the system and creating an arc flash that fused his contact lenses to his corneas. After removing his lenses, a significant amount of contact lens-fused corneal tissue sloughed off with them and caused severe bilateral corneal scarring and blindness. So what actually happened to this worker? While the welder did create an arc flash, he did not report the incident until the next day when he was diagnosed with 2 large corneal ulcers. Both ophthalmologists who treated him agreed that his corneal ulcers were caused by overwearing his polymethylmethacrylate (PMMA) lenses for about 12 to 17 hours after the accident and not by the arc flash.1,7,8 Both ulcers healed after 2 days, and the worker completely regained his vision without suffering any vision loss. During the 1960s and 1970s, several other similar unverified welding accidents involving contact lenses were reported both in the United States and internationally. For example, it was reported that a French welder was blinded in a welding accident involving a 440-volt power source that fused his contact lenses to his eyes.1 However, France does not use that specific voltage level, so the accuracy of the report was highly questionable. After a lengthy study sponsored by the French National Institute for Research and Safety, the report was found to be “the creation and escalation of a chain of rumors, with the ultimate result being the reporting of an accident that did not occur.”1 Researchers have attempted to replicate these conditions and fuse a contact lens to the cornea but have never succeeded.3 When contact lenses are heated, they experience a temperature increase that is more marked as the lens thickness increases. However, the temperature increase is not nearly high enough to cause a contact lens to fuse to the cornea without violating basic physical principles of matter.3 Heat is dissipated in a contact lens either by conduction, convection, or radiation. Studies have found that any heat generated “from a welding arc or electrical spark is not intense enough to dry up the eye’s fluid, nor could a contact lens concentrate rays to intensify the heat.”3,8 Only a radiation injury from not wearing proper ultraviolet (UV) protection could provide the extremely high energy levels that are required for contact lens corneal fusion. Although the welder’s injuries were similar to those of a radiation burn, he was wearing proper UV protection, so that was unlikely. Also, radiation damage would have caused an immediate onset of symptoms that would not have appeared 12 to 17 hours after the accident. Based on these and other similar findings, the Contact Lens Association of Ophthalmologists3 in a 1983 policy statement stated that contact lens wear does not increase the risk of ocular damage while arc welding. In spite of the overwhelming evidence refuting the contact lens corneal fusion theory, it still has proponents who believe that the arc flash creates microwaves that instantly evaporates the tear film and causes the contact lens to fuse to the cornea, resulting in permanent vision loss upon removal of the contact lens.2 Research has found that arc flashes are not capable of creating microwaves that possess enough energy to instantly evaporate the tear layer.9 In
597 addition, because of the thermal response produced in the tissue by microwaves,4 it would be impossible to have enough microwave energy to instantaneously evaporate the tear film and fuse a contact lens to the eye and yet spare the worker from receiving severe burns to the body. In fact, if such a scenario was possible, the worker would be instantly “cooked” and would not survive the accident. Another contact lens myth was popularized by a respected industrial ophthalmologist in the 1960s. He published another undocumented accident about an engineer who was wearing contact lenses and safety goggles and was splashed with a 50% caustic solution.5 Supposedly, this highly caustic solution was rinsed off his face, but the victim sustained severe corneal chemical burns. The ophthalmologist reported that the engineer’s contact lenses were responsible for the vision loss because they prevented the solution from being completely rinsed from his eyes before it caused severe ocular injuries.5 However, blaming these injuries on the contact lenses is difficult because properly worn safety goggles will easily prevent splashed chemicals from reaching the eyes. Based on the description of the accident, it is much more likely that safety goggles were either never worn or were not protecting the worker’s eyes when the accident occurred. Workers have a tendency to ignore PPE requirements unless their compliance is monitored and enforced. The Bureau of Labor reports that as many as 60% of workers who have suffered workplace ocular injuries were not wearing their ocular PPE at the time of the accident.3 In fact, 90% of all eye injuries could have been prevented had the individual taken the necessary safety precautions.10
The negative effect of the myths on contact lens use in industrial and chemical environments Industrial accidents are always considered newsworthy, and these supposed contact lens accidents are no exception. Media outlets continually resurrect and sensationalize these reports every few years even though they have been conclusively disproved. More importantly, these reports still continue to adversely influence industrial and chemical companies’ contact lens wear policies. Although there are instances in which contact lenses have contributed to or worsened an injury, Messana2 reports that contact lenses have been shown to either reduce or completely prevent injury 97% of the time. In fact, for every worker whose ocular injuries have been worsened by contact lens wear, there are nearly 30 other workers who were exposed to similar circumstances but whose contact lenses either prevented injury or did not increase its severity.2 Messana’s opinions have been supported by the federal government as well as by chemical and medical professional associations. In its PPE Final Rule, the Occupational Safety and Health Administration (OSHA) stated that “con-
598 tact lenses do not pose additional hazards to the wearer and additional regulation is unnecessary.”2 In addition to OSHA’s approval, the American Chemical Society’s (ACS) Committee on Chemical Safety and the American Optometric Association (AOA) have released position statements that address contact lens wear in the workplace. The ACS committee has stated that in many workplaces that handle hazardous chemicals, workers are “prohibited or discouraged” from wearing contact lenses as a result of “earlier statements based on rumors and perceived risks,” which has been proven to be unfounded.2 Realizing that contact lenses have either reduced or completely eliminated injury in a wide variety of workplace situations, they recommended that employers should permit contact lens wear in most workplace areas as long as those who wear contact lenses, wear the same PPE required of other workers.2 The AOA’s statement supported this decision and also refuted some of the common misconceptions that contact lenses negate the protection provided by safety equipment or make the cornea more susceptible to damage by optical radiation.2 They concluded by emphasizing that workplace contact lens wearing regulations must not be “based on perceived hazards, random experience, isolated unverified case histories, or unsubstantiated personal opinions.”2 In spite of these opinions from OSHA and the scientific and optometric communities, confusion over the safety of contact lenses is still common in industrial and chemical workplaces. In a 1994 survey of academic institutions that examined contact lens wear policies in chemical environments, Segal5 found that only 57% of the 26 responding institutions allowed contact lens wear. Three years later in 1997, Segal5 repeated the survey to determine if academic institutions had modified their safety policies in response to current research that supported the use of contact lenses when combined with standard PPE requirements. This time, besides only examining the contact lens polices of academic institutions, Segal expanded her survey to compare the contact lens wear and safety policies of industrial and chemical companies with that of academia. She found that although 77% of the 26 responding academic institutions now permitted contact lens wear, only 58% of the 26 responding industrial and chemical companies allowed contact lenses. This highlights the tendency of academic institutions to be more aware and accepting of current research, whereas industry reacts more slowly and cautiously to change unless significant financial savings justify revising their outdated yet effective safety practices.
Ocular protective benefits In 1974, Rengstorff and Black11 examined 128 documented industrial accidents that resulted in ocular injury, physical trauma, or hazardous exposure in contact lens wearers. These injuries ranged from exposure to chemical splashes and fumes to assorted metal foreign bodies and projectiles.
Optometry, Vol 78, No 11, November 2007 The authors concluded that although the contact lenses often were severely damaged, they consistently prevented or lessened the resultant injury to the cornea and other ocular structures. When combined with appropriate PPE, the contact lens provided additional protection for workers in many common industrial and chemical workplace conditions by providing protection and limiting damage from chemicals, fumes and vapors, trauma, foreign bodies, and environmental extremes.
Protection against chemical exposure The first protective benefit of contact lenses is that they provide varying levels of additional eye protection against acidic and alkaline chemical solutions. When working with chemicals, it is always critical that workers utilize proper PPE and follow standard safety precautions. However, if workers are noncompliant with their PPE, contact lenses will provide protection that would not be afforded to non– lens wearers. Research has found that although contact lenses absorb chemicals and vapors, it is unlikely that these substances would diffuse completely through the lens to reach the anterior surface of the cornea.2 In fact, this absorption process assists in protecting the cornea by allowing the contact lens to absorb some of the offending chemicals and thus decrease both the amount and time of chemical ocular exposure. This greatly reduces the severity of a resulting ocular injury as well as limiting the possibility of visual acuity loss. When working with highly concentrated corrosive acidic and alkali solutions, contact lenses provide little to no protection. These solutions are so corrosive that the protective barrier formed by the contact lens is penetrated quickly, such that a worker wearing contact lenses without PPE will suffer severe injury if the chemical is not immediately removed. Working with alkaline solutions requires the most caution, because they are more corrosive than an acid of equivalent strength and are thus able to penetrate tissue faster than acids, causing a more severe injury in a shorter amount of time. A 1982 study by Nilsson and Andersson12 found that contact lenses do not provide any protection against caustic solutions above 20%, although contact lens usage does not worsen the resulting injury as has been commonly believed. Inasmuch as acids have a slower penetration time, contact lenses provide a protective shield over the cornea that either prevents or reduces the possibility of ocular injury. This protective effect only lasts for a short period and is dependent on the acidic concentration, exposure time, and contact lens thickness, but has been shown to significantly limit or prevent ocular injuries. Nilsson and Andersson12 also found that when high plus hydrogel contact lenses are exposed to hydrochloride concentrations ranging from 20%, the resultant corneal damage is decreased by 75%. Although proper PPE must always be used when working with chemicals, in most instances contact lenses provide protection that could make the difference
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between a worker being blinded or saving that worker’s vision. In industry, conventional wisdom has always dictated that in the event of an accident, contact lenses would not be able to be quickly removed from the victim’s eye and would interfere with emergency eye irrigation. The fear was that the chemical would become trapped underneath the contact lens where it could not be rinsed away. However, when the eye is aggravated by a foreign body, chemicals, or a pain response, the lid blepharospasm reflex immediately forces the eye tightly shut. This happens so quickly that the contact lens is temporarily suctioned to the eye and the tears between the cornea and posterior surface of the contact lens create a barrier that prevents the chemical from getting to the cornea, reducing the severity of corneal damage.9,13 Blais10 reports that several researchers have found that contact lenses do not interfere with ocular irrigation, because the contact lenses are frequently flushed out. This occurs because the initially tight seal between the contact lens and the cornea weakens and allows the irrigating solution to flow easily underneath the lens to rinse away the contaminant and flush out the contact lens during irrigation of the eye. Blais10 states that “eyes with contact lenses and proper irrigation can be saved regardless of whether the lenses are removed during or after irrigation.”
Protection from chemical fumes and vapors Another concern associated with working with chemicals is the fumes and vapors that result from routine laboratory procedures. Although all chemistry laboratories utilize fume hoods for working with noxious chemicals, usually residual vapors are present in the laboratory. For years, contact lens wear was contraindicated when working with all vapors, but it is now known that vapors actually have varying effects on contact lenses. For example, a 1985 Italian study discovered that isopropyl and ethyl alcohol vapors penetrate hydrophilic lenses where they are absorbed and later leased into the wearer’s tear film.5 Similarly, a 1978 OSHA report recommended that contact lenses not be used “when working with acrylonitrile, 1,2 dibromo-3-chloropropane, ethylene oxide, methylene chloride, and 4,4-methylene dianiline chemicals.”7,14 However, studies have also found that when exposed to certain other vapors, contact lenses can provide additional protection. Nilsson and Andersson12 found hydrogel contact lenses decreased the exposure to trichloro-
Table 1 lenses
Ocular chemical protection provided by contact
Reduce or eliminate injury from exposure to acidic chemical solutions. Reduce or eliminate injury from exposure to alkaline chemical solutions of 20% and below. Reduce or eliminate ocular exposure from many fumes and vapors.
599 ethylene and xylenne vapors when compared with the exposure found in a non– contact lens–wearing eye. A similar study conducted by the Ophthalmology Department at the University of Nebraska tested the absorption of acetone, diethyl ether, trichloroethylene, and toluene in contact lenses and found that contact lens wearers exhibited decreased ocular exposure when exposed to volatile organic solvents.5 Other examples of contact lenses protecting against vapors have been observed. When soft contact lens wearers cut onions, they do not experience the “excessive tearing” that affects non–lens wearers. The soft contact lenses absorb and thus protect against the tearing stimulating allyl dissulfides that are released into the air when the onion is cut.5 A similar protective effect against tear gas has been documented by Dutch police authorities who do not require their soft contact lens wearing officers to wear gas masks when using tear gas. Aalphen15 found that when soft contact lens wearers are exposed to high concentrations of tear gas in a gas chamber, they were able to see clearly upon leaving the chamber and suffered no other physical signs of discomfort other than slight conjunctival injection. However, non– contact lens–wearing officers without a gas mask were only able to endure the chamber for a maximum of 2 minutes and could not open their eyes for, at most, 1 minute after leaving the chamber. Additionally, they also experienced nausea and vomiting and exhibited mild epithelial corneal staining.15 Aalphen15 concluded that the officers in the study who wore the soft contact lenses “kept their eyes open more easily and had quicker and better orientation.” This significantly improves their ability to use tear gas in riot control situations and eliminates the possibility that officers will become incapacitated by the gas if their gas mask is either dislodged or damaged (see Table 1).
Protection from mechanical trauma, foreign bodies, and particles Besides providing additional eye protection against chemicals and vapors, both hard and soft contact lenses have been found to provide varying levels of protection against mechanical trauma such as contusions, concussions, particles, and foreign body injuries. Contusion and concussion injuries are closely related, because often a contusion may also result in a concussive injury. Contact lenses are able to decrease some of the severity of a contusion by absorbing energy, which helps decrease the chance of a contra-coup injury, a retinal detachment, or another form of traumarelated retinal damage.4,11,16 How do rigid and soft contact lenses provide protection against blunt trauma, foreign bodies, and projectiles? Cases have been reported in literature in which hard lenses fractured after sustaining blunt trauma from field hockey sticks, fists, and other objects, yet the incident resulted in minimal or no corneal damage.4,11 Rigid lenses provide a physically hard barrier that acts as a shield that deflects a blow to the cornea. In a study by Chou et al.,16 an air gun fired
600 pulverized iron fillings into the eyes of pig cadavers wearing either rigid gas-permeable contact lenses or soft contact lenses. With rigid gas-permeable contact lenses, the only damage that occurred was to the exposed corneal surface not covered by the lens. Although hard lenses provide effective protection against blunt trauma and some small high-speed particles, they provide little protection against large sharp high-speed particles and dust and can trap small foreign bodies underneath the lens.4 Cullen4 reports that a 1981 study found that hard lenses were more likely to shatter and cause corneal damage from the lens shards when hit by large sharp projectiles as opposed to other types of contact lenses. However, in this study, the air gun and projectile were fired only 6 mm from the cornea and the majority of the projectile remained in the barrel of the air gun. This provided a constant force on the contact lens and did not allow the particles to be deflected at impact. Although this accurately measures the force needed to break a hard lens, it is extremely unlikely that this type of trauma would occur outside the controlled environment of the laboratory. Because of the fit of a hard lens on the cornea, it is susceptible to dust and particles in the tear film and on the conjunctiva, which can work their way behind the hard lens. Although these findings would seem to indicate that hard lenses are contraindicated in workplace conditions in which dust and particle exposure is likely, this is not necessarily true. Nichols and Good3 recommend that “with proper eye and face protection . . . hard contact lens wear should not create an additional hazard around flying particles.” However, they cautioned that workers “should wear rigid contact lenses with caution when working around dust and smoke particles because the particles’ entry behind the lens could visually incapacitate workers and place them at risk of further injury.”3 Like hard lenses, soft lenses can provide protection that varies depending on the type of foreign body and the thickness, rigidity, and water content of the lens.4 Lowwater soft contact lenses provide a protective benefit by absorbing some of the impact and lessening the blow the eye receives when struck by a foreign body. This occurs because the design of the soft contact lens greatly increases the necessary energy needed by a foreign body to perforate the contact lens and cornea. Chou et al.16 found that pig eyes fitted with soft contact lenses were well protected, because only 3 of 11 eyes received a mild corneal abrasion, whereas all 11 control eyes without soft contact lenses had severe corneal damage. However, unlike the hard lenses, nearly every soft lens was destroyed by the testing. Cullen4 reports that in a 1981 Nilsson study high-water soft lenses did not provide protection from high-speed large sharp particles, whereas low-water soft lenses provided significant protection against the ability of a foreign body to penetrate the contact lens and cornea. Cullen4 states “while foreign bodies may be trapped beneath rigid lenses, this does not happen with hydrogel lenses unless the speck is inserted with the lens.” During
Optometry, Vol 78, No 11, November 2007 Table 2 Corneal protection provided by contact lenses against physical hazards Mechanical trauma Foreign bodies Particles Temperature extremes High winds
Operation Desert Storm, pilots reported that their soft contact lenses adapted well to the dry sandy desert conditions and that they did not experience discomfort or foreign body sensations.9 The larger size and tighter fit of the soft contact lens prevents particles from getting underneath the lens and protects the wearer from particles that would otherwise cause discomfort, tearing, and decreased vision.
Protection from cold temperature extremes and high winds The last protective benefit of contact lenses is the protection they provide from physical and environmental hazards. Compared with a rigid lens, the larger diameter of soft contact lens provides a greater area of corneal coverage and helps to protect limbal stem cells.3 Protection of these cells is vital inasmuch as it ensures that the corneal epithelial layer is able to regenerate when abraded or damaged. However, one study for the United States Navy found that smaller rigid lenses can provide similar protection. This study exposed rabbits to temperatures of ⫺28.9°C and 125 mph winds for several hours while wearing rigid hard lenses. The rabbit subjects suffered only minimal ocular damage and Socks17 concluded that “contact lenses may be acceptable and may even offer protection to the eyes from wind-driven ice and snow in cold environments” (see Table 2).
Increased workplace performance and visual comfort Increased field of view and decreased distortions In addition to providing ocular protection, contact lenses provide many specific visual benefits such as a wider field of view, reduced aberrations, and freedom from the inherent restrictions that accompany spectacle wear. One of the most important benefits provided by contact lenses is that the visual field of a contact lens wearer is only limited by the field of fixation compared with the limits caused by the size of the spectacle lenses and frame.18 Unlike spectacles, contact lenses move with the eye and allow the wearer to always look through the optical center of the contact lens, maximizing visual acuity and field of view. However, with spectacles, wearers are forced to move their heads to see objects that fall outside the field of view provided by the
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glasses. Compounding this problem is that spectacle lenses, according to Preuss, create prismatic distortions that reduce the visual field in spectacle wearers with higher refractive errors.6 These distortions are caused whenever the wearer looks into the lens periphery and away from the optical center of the lens.
Reduced aberrations, reflections, and glare Spectacle lenses are not perfect optical systems and thus are subject to various aberrations that can decrease vision and cause visual discomfort. Although some aberrations are minor and have little impact, 3 specific aberrations, oblique astigmatism, distortion, and curvature of field, all decrease the quality of vision through spectacle lenses, especially in prescriptions with high refractive errors. These aberrations all occur to varying degrees when looking through the periphery of a spectacle lens.19 However, with contact lenses, the wearer only looks through the optical center of the lens and not through the periphery, eliminating oblique astigmatism and curvature of field. Distortion, which is also affected by the distance between the spectacle lens and pupil, as well as the power of the peripheral lens, is minimized by the contact lens sitting directly on the eye.18 This is why contact lens wearers typically can see better with contacts than they can with glasses; the optical aberrations present in spectacles are either minimized or completely eliminated. Another visual benefit provided by contact lenses is that they are not subject to the annoying reflections and glare that can be caused by spectacle lenses and frames. Reflections and glare result whenever light is incident upon 2 surfaces with different refractive indices and are created when light enters from either the front or the back surface of the lens. Optically, the design of spectacle lenses creates 5 specific types of reflections. Of these, 3 result from reflections produced by light entering in front of the spectacle lens and being reflected back between the cornea and the front and back surfaces of the lens. Similarly, the other 2 result from light entering from behind the spectacle lens and reflecting off the front and back surface of the lens. However, once a contact lens is placed on an eye, light is unable to enter behind the lens, and 2 sources of glare are immediately eliminated.18 Additionally, reflections and glare increase in larger spectacle lenses, where increasing the lens surface area degrades its optical properties. However, with the greatly reduced lens surface area of contact lenses, these reflections are minimized and usually not observed by the contact lens wearer, resulting in a corresponding visual acuity improvement. Although antireflective coatings may be used with spectacle lenses, they are only able to eliminate glare from certain wavelengths of light, and the coating attracts dust, making them difficult to keep clean, especially in dirty workplace environments. For spectacle wearers who tend to scratch their lenses or are exposed to solvents and particles that can damage the antireflective coating, they will experience problems with glare and halos that will in most cases cause them to report decreased vision and increased discomfort.
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Visual freedom from spectacles Contact lenses provide workers with other significant benefits, such as complete freedom from reliance on spectacle lenses. No longer will they need to worry about having their spectacles knocked off, finding themselves unable to safely perform their duties. Furthermore, if their spectacles were knocked off or broken, many workers might be unable to see clearly enough to finish their task and could become a safety hazard not only to themselves but to those around them as well. Although it is possible that a contact lens could become dislodged, it rarely happens and is especially unusual with soft contact lenses. However, even if a contact lens was dislodged, the binocular worker would still be able to see clearly with the other eye, and would be much more likely to be able to either complete or stop a current task without self harming or to others. A survey by Good and Augsburger20 found that approximately 52% of police officers have had their glasses dislodged while on duty. Contact lenses essentially eliminate this risk inasmuch as once they are in the eyes, they are unable to be broken, are extremely difficult to dislodge, and provide consistently clear vision in a wide variety of circumstances.
Safety benefits for respirator use The importance of workplace spectacle lens freedom has been highlighted by efforts firefighters made to reverse a longstanding OSHA decision that banned contact lens use while using full-faceplate respirators. Contact lenses were originally banned because it was believed that users faced an increased risk of either being visually incapacitated by dust from their air supply being blown under their contact lenses or by having a contact lens become dislodged, block the mask’s air flow, and suffocate the wearer.8 However, after discovering that contact lenses provided a wider field of view and ensured an airtight seal between the mask and wearer’s face, firefighters ignored the ruling and used them without any ill effects. After all, comfortably wearing spectacles underneath the faceplate of a respirator is difficult, as some frame shapes and styles prevent the respirator masks from creating a proper seal, inadvertently exposing wearers to environmental hazards from which they are trying to protect themselves.7 In 1995, after preliminary surveys reported improved performance and safety, OSHA funded a study to reexamine the previous 1969 decision. This study confirmed the 1995 survey results, so OSHA concluded that “contact lenses do not pose additional hazards to the wearer, and has determined that additional regulation addressing the use of contact lenses is unnecessary” and approved contact lenses for respirator use.21
Environmental vision benefits and UV protection Contact lenses offer protection against environmental changes and fluctuations that decrease vision. According to Good and Augsburger,20 56% of spectacle-wearing police
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Table 3 Visual workplace benefits of contact lenses over spectacle lenses Increased field of view. Reduced optical aberrations and distortions. Increased safety when used with appropriate PPE. Vision not affected by rain, fog, or snow. Improved confidence and self-image.
Improved visual acuity. Reduced reflections and glare. Freedom from spectacle dependency. Difficult to dislodge. Improved cosmesis.
officers have had to remove their glasses when rain, fog, or snow blurs or distorts their vision. This decreases the safety and efficiency of workers, especially outdoor workers, whose glasses and consequently vision are negatively affected by environmental changes. Today, contact lenses are available that block UV radiation and help protect the cornea, lens, and parts of the conjunctiva. UV rays have been implicated in cataract formation, so UV-blocking contact lenses help protect the crystalline lens from irreversible cumulative damage, which is not only caused by sunlight, but by popular fluorescent lighting as well.
Social and psychological benefits of contact lens wear The final benefit of contact lenses is the resulting visual freedom the lenses provide, enhancing the psychological, emotional, and physical functioning of the worker in the workplace. Once people begin to wear contact lenses and realize how much vision can be improved, they do not want to have to return to spectacle wear again. Cullen22 said that “most successful contact lens wearers wish to wear their contact lenses in all aspects of their lives, including the workplace.” It has been found that the use of contact lenses helps improve workplace communication (besides improving cosmesis); some workers feel that their eyes are hidden by their spectacles and believe that their communication abilities are better without them. This is especially true when the spectacle lens is noticeably thick or if it magnifies or minifies the wearer’s eyes.18 Better cosmesis increases worker confidence, self-esteem, and communication ability and improves workplace performance (see Table 3).
Precautions and contraindications for workplace contact lens wear Chemical vapors Contact lens wear is not recommended when working with acrylonitrile; 1,2 dibromo-3-chloropropane; ethylene oxide; methylene chloride; 4,4-methylene dianiline; or isopropyl
and ethyl alcohol vapors.5,7,14 The preamble to OSHA’s guidelines does not include the specific basis for their recommendation, but it is likely based on the potential for the contact lens to absorb the vapor and release it into the tear film.23 This occurrence would be minimized by fitting workers who work with these chemicals with daily disposable contact lenses, which would ensure that any residual vapor in the lens would not be in contact with the eye for a significant amount of time. By combining goggle use (which would be required of contact lens wearers and non– contact lens wearers alike) with daily disposable lenses, contact lenses would likely be safe to wear in these environments.
High temperatures Some workplace environmental conditions can make successful contact lens wear difficult for certain workers, although they can still successfully wear contact lenses. Although studies have shown the minimal effect of extremely cold temperatures on corneal health, direct corneal contact with high-temperature objects will cause variable corneal damage that is dependent on the temperature and time of exposure.4,17 Hoffmann and Kunz24 found that a 1- or 2-minute direct corneal exposure of water heated to 47°C caused a mild superficial keratitis, whereas temperatures of 80°C resulted in corneal clouding and edema. Although worker exposure to these types of direct heat is unlikely, some workers, especially those who work with smelters, ovens, and furnaces, are routinely exposed to much hotter air temperatures. In fact, the air temperature in a typical sauna can reach between 80° to 100°C. Inasmuch as only the air temperature is elevated, no direct corneal damage is caused in this environment except for increased rate of tear film evaporation that dries out contact lenses and causes dry eye symptoms.4 This dryness can be treated by educating workers to increase their blink rate and having them use artificial tears or lubricating drops as needed during the workday.
The effects of high altitudes and low humidity Altitude-related contact lens problems may be especially difficult for aviation workers such as pilots, aircrew, stewardesses, and individuals who work at altitudes ranging from 4,000 to 9,144 meters. One study simulated an altitude of 9,144 meters and found that subjects using supplementary oxygen had no problems except for a few reporting “dry and tired” eyes.25 However, Castren et al.,26 when simulating a high-humidity environment at an altitude of 4,000 meters, reported that “corneal erosions and stromal opacities” were observed in subjects wearing contact lenses. Although these findings are important, the study is not particularly applicable inasmuch as aircraft travel creates a low-humidity environment rather than the high-humidity conditions created by Castren’s study. Additionally, in
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Table 4 Possible environmental workplace contraindications for contact lens wear High temperature environments High altitudes Low humidity Certain chemical vapors
1988, Flynn et al.27 reported that although corneal thickening increases at high altitudes, the small resultant myopic shift does not affect pilot vision, as a result of “13 years or more of experience of pilots in the Swedish and other air forces.” They concluded that hydrogel contact lenses may be worn safely while flying military aircraft. Once the humidity level falls below 11%, contact lenses begin to dry out, and the tear break up time begins to decrease. This decreases the lens radius of curvature, lens movement, and oxygen transmissibility and makes the lens more susceptible to deposits. Inasmuch as movement and tear exchange are critical for successful contact lens wear in these patients, practitioners fitting these workers must ensure that their lenses are not fit too tightly.4 Contact lens wearers will also benefit from a frequent replacement schedule, adding enzymatic cleaners to their cleaning regimen, and receiving instructions not to overwear their contact lenses. Additionally, Cullen4 reports that the newer highwater-content contact lenses have decreased both the incidence and severity of dryness symptoms that have always been caused by high altitude and low-humidity environments. Fitting these patients into high-water lenses maximizes ocular comfort and decreases or eliminates dry eye symptoms (see Table 4).
Patient education and lens fitting recommendations It is critical for practitioners to thoroughly educate workers who plan to wear contact lenses in industrial or chemical environments that, although their contact lenses do provide additional protective benefits, they are not PPE, and workplace standard PPE requirements along with general safety practices must always be followed. It is also recommended that workers who work with chemical agents be fitted with daily disposable contact lenses. These workers also must be educated about the importance of having a backup pair of spectacles at their workplace in case they ever experience discomfort, redness, irritation, or eye pain and need to remove their lenses.4 Finally, practitioners considering fitting gas-permeable lenses must ensure that workers are not placed in situations in which they can be visually incapacitated by a foreign body. Nichols and Good3 advise that workers must be able to “safely call timeout and easily cease operations to remove the contact lens and attend to the foreign body” that disrupts their vision. This is especially critical in environments that
603 are dirty, dusty, or windy.3 These environments cause gaspermeable lenses to have a higher incidence of foreign bodies becoming trapped behind the lens and disrupting vision. In hazardous workplace environments that involve welding, working at heights, some types of construction work, and operating heavy machinery or construction equipment, a sudden loss of vision can not only endanger the safety of the gas-permeable lens wearer but others as well. It is much less likely for soft contact lens wearers to become incapacitated by foreign bodies or particle matter than gas-permeable lens wearers, and thus soft contact lenses are recommended for these environments (see Table 5).
Discrimination against workplace contact lens wear and policy recommendations Workplaces that enforce outdated contact lens policies that either disqualify contact-lens-wearing workers from certain job positions or require contact lens wearers to use additional PPE not required of non– contact lens wearers, violate the Americans with Disabilities Act (ADA).5 Under this act, employers are not allowed to remove or reassign workers if the worker still can “perform the essential functions of the position with or without accommodation without substantial risk of threat to themselves or others.”5 Contact lenses for medical applications are an approved accommodation method except in the rare instances in which contact lenses have been conclusively proven that the lenses “pose a direct threat to the health and safety” of the worker or others.5 Blais1 concurs, stating that “there is no justification for employers to discriminate against employees who wear the visual accommodation required for them to perform their essential functions.” Employers who do so may be in violation of the ADA which is equivalent to denying a worker employment on account of age, race, or religion. Additionally, the ADA prohibits employers from requiring contact lens wearers to use PPE that is not required for non–lens wearers. Inasmuch as contact lenses have been shown to increase workplace safety, it is discriminatory to force contact lens wearers to use PPE they do not need and that non– contact lenses wearers do not have to use. This not only creates additional worker and company expenses, but may strain worker relationships and create problems and
Table 5
Workplace contact lens fitting pearls
Always educate all contact lens patients about the importance of wearing proper PPE. Fit workers who work around chemicals with daily disposable lenses. Recommend workers keep a backup pair of spectacles at their workplace. Fit patients exposed to dirty, dusty, or windy environments with a soft lens instead of a gas-permeable lens.
604 distractions that decrease employee performance and productivity. Workplace contact lens safety experts, the American College of Occupational and Environmental Medicine, the American Academy of Ophthalmology, and the American Optometric Association all recommend that industrial and chemical companies create written corporate contact lens policies.1,22,23 These policies should list the required jobspecific PPE, plant locations where PPE use is required, and whether contact lens wear is banned or limited in any particular work area. It is critical that these policies are flexible enough to evaluate individual worker needs on a case-by-case basis to ensure that they are provided with a refractive correction that maximizes their vision and ocular safety. If industrial and chemical workplaces already have established written contact lens policies, they must be reviewed to ensure that they are current and recognize the safety of workplace contact lens use. Additionally, companies must verify that their policies comply with the ADA by ensuring that all contact lens wearers are not discriminated against, regardless of why they wear them. Finally, all policies should highlight how contact lenses, when worn with standard PPE, are safer than spectacles in most workplace situations, because not only do they provide physical protection against environmental hazards, they also provide several other visual benefits that improve visual comfort and attitude and contribute to increasing employee satisfaction and productivity.
References 1. Blais BR. Discrimination against contact lens wearers. J Occup Environ Med 1998;40:876-80. 2. Messana K. The last word on contacts. Occup Health Saf 2001;70: 68-70. 3. Nichols JJ, Good GW. Contact lenses and the work environment [Contact Lens Spectrum Web site]. November 2003. Available at http://www.clspectrum.com. Last accessed March 14, 2005. 4. Cullen AP. The environment. In: Bennett ES, Weissman BA. Clinical contact lens practice. Philadelphia, PA: J.B. Lippincott; 1991:1-28. 5. Segal EB. Contact lenses and chemicals. Chem Health Safety 1997; 4:33-7. 6. Preuss A. The world of contact lenses. Chem Health Safety 1995;2: 12-5.
Optometry, Vol 78, No 11, November 2007 7. American College of Occupational and Environmental Medicine. The use of contact lenses in an industrial environment [ACOEM Web site]. May 2003. Available at http://www.acoem.org. Last accessed March 14, 2005. 8. Segal EB. Contact lenses and chemicals: An update. Chem Health Safety 1995;2:16-21. 9. Blais BR. Does wearing of contact lenses in the workplace post a direct threat. The Occupational and Environmental Medicine Report 1998;12(3):17-31. 10. Blais BR. Contact lenses in industry: The ongoing discussion. Chem Health Safety 1997;4:22-6. 11. Rengstorff RH, Black CJ. Eye protection from contact lenses. J Am Optom Assoc 1974;45:270-6. 12. Nilsson SEG, Andersson L. The use of contact lenses in environments with organic solvents, acids, or alkalis. Acta Ophthalmologica 1982; 60:599-608. 13. Petreycik RM. Contact lenses in the workplace: more than meets the eye. Safety and Health 1997;155:74-7. 14. Code of Federal Regulations-Parts 1900 to 1910 Personal Protective Equipment. 29 CF2R 1910.I32. Revised 1994. 15. Aalphen CC. Protection of the police against tear gas with soft lenses. Mil Med 1985;150(8):451-3. 16. Chou B, Ritzmann E, Anthony P. Ocular protection by contact lenses from mechanical trauma. International Contact Lens Clinic 1992; July/August:162-6. 17. Socks J. Contacts lenses in extreme cold environments: response of rabbit corneas. Am J Optom Physiol Optics 1982;59:297-300. 18. Fannin TE, Grosvenor T. Optics of contact lenses. In Fannin TE, Grosvenor T, eds. Clinical Optics. Boston, MA: Butterworth-Heinemann: 1996:196-203, 373-405. 19. Pedrotti LS, Pedrotti FL. Optics and Vision. Upper Saddle River, NJ: Prentice-Hall; 1998:122-39. 20. Good GW, Augsberger AR. Uncorrected visual acuity standards for police applicants. J Police Sci Admin 1987;15:18-23. 21. Code of Federal Regulations-Parts 1910 and 1926 Respiratory protection final rule. Fed Reg. Vol. 63. no 5, Thursday, January 5, 1998 Rules and Regulations, pp 1162. 22. Cullen AP. American Optometric Association guidelines for the use of contact lenses in the industrial environments. In: Good GW, Stephens GL, Pitts DG, et al, eds. American Optometric Association Occupational Vision Manual. St. Louis, MO: AOA, 2002;23-4. 23. Schulte P, Ahlers H, Jackson L, et al. Current Intelligence Bulletin 59: Contact lens use in a chemical environment. National Institute for Occupational Safety and Health 2005;1-3. 24. Hoffmann W, Kunz E. Uber Warmeschadigungen des Auges. Grasefes Arch Clin Exp Ophthalmol 1934;132:155-84. 25. Eng WG, Rasco JL, Marano JA. Low atmospheric pressure effects on wearing soft contact lenses. Aviat Space Environ Med 1978;49:73-5. 26. Castren J, Tuovinen E, Lansimies E, et al. Contact lenses in hypoxia. Acta Ophthalmologica 1985;63:439-42. 27. Flynn WJ, Miller RE, Tredici TJ, et al. Soft contact lens wear at altitude: effects of hypoxia. Aviat Space Environ Med 1988;59:44-8.
The safety and efficacy of contact lens wear in the industrial and chemical workplace Keith Tyhurst, O.D.,a Ryan McNett, O.D.,b and Edward Bennett, O.D.c a
Marion Eye Centers & Optical, Marion, Illinois; bRyan M. McNett, O.D., L.L.C., Wichita, Kansas; and cUniversity of Missouri College of Optometry, St. Louis, Missouri. KEYWORDS Contact lenses; Industrial safety; Workplace safety; Chemical safety; Contact lens injury; Ocular injury; Personal protective equipment
Abstract BACKGROUND: The use and safety of contact lenses in the industrial and chemical workplace has often been questioned since the 1960s because of many unconfirmed reports of ocular injury resulting from contact lens wear. Because of these urban legends, contact lens wear has been banned or wearers have been required to wear additional personal protective equipment (PPE) not required of non-contact lens wearers. METHODS: Literature review via Medline and Google search. RESULTS: Research has shown that contact lenses typically provide protective benefits that decrease the severity of ocular injury and improve worker performance. While contact lens wear contraindications do exist, in most cases, and with proper precautions, contact lens wear is still possible. CONCLUSIONS: Industrial and chemical companies need to establish written contact lens use policies based on current studies that have shown the safety of workplace contact lens wear when combined with the same PPE required of non-contact lens wearers. Practitioners need to discuss, with their contact lens patients, the additional responsibilities required to maintain proper lens hygiene and proper PPE in the workplace. Optometry 2007;78:596-604
protective benefits against a wide range of environmental workplace hazards when combined with that job’s standard PPE requirements.2 Additionally, contact lenses provide workers with many other visual benefits that allow the wearers to function more efficiently in the workplace than spectacle wearers. Although some environmental or workplace conditions limit or contraindicate contact lens wear, contact lenses have been shown consistently to supplement worker eye protection and provide visual benefits that improve worker performance and job satisfaction.4-6
For the last 40 years, the safety and benefits of contact lens use in industrial and chemical workplaces often has been questioned, causing employers and safety officers to view contact lenses with apprehension.1,2 Numerous popular industrial horror stories have linked contact lens usage with severe ocular injuries, and the negative effects of these legends on company safety policies has caused contact lens wearers to be discriminated against by their employers, who have either banned contact lens wear completely or forced wearers to use extra personal protective equipment (PPE) that is not required of non– contact lens wearers.1,3,4 These additional PPE requirements have been consistently and conclusively shown to be unnecessary by research that reveals that, in most cases, contact lenses provide ocular
Famous contact lens myths
Corresponding author: Keith Tyhurst, O.D., Marion Eye Centers & Optical, 1200 W. DeYoung, Marion, Illinois 62959. E-mail: [email protected]
The most famous industrial contact lens myth originated from an undocumented 1967 incident.7 Supposedly, an arc welder who was wearing soft contact lenses underneath his welding faceshield connected to a 440-volt power line,
1529-1839/07/$ -see front matter © 2007 American Optometric Association. All rights reserved. doi:10.1016/j.optm.2007.02.021
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shorting out the system and creating an arc flash that fused his contact lenses to his corneas. After removing his lenses, a significant amount of contact lens-fused corneal tissue sloughed off with them and caused severe bilateral corneal scarring and blindness. So what actually happened to this worker? While the welder did create an arc flash, he did not report the incident until the next day when he was diagnosed with 2 large corneal ulcers. Both ophthalmologists who treated him agreed that his corneal ulcers were caused by overwearing his polymethylmethacrylate (PMMA) lenses for about 12 to 17 hours after the accident and not by the arc flash.1,7,8 Both ulcers healed after 2 days, and the worker completely regained his vision without suffering any vision loss. During the 1960s and 1970s, several other similar unverified welding accidents involving contact lenses were reported both in the United States and internationally. For example, it was reported that a French welder was blinded in a welding accident involving a 440-volt power source that fused his contact lenses to his eyes.1 However, France does not use that specific voltage level, so the accuracy of the report was highly questionable. After a lengthy study sponsored by the French National Institute for Research and Safety, the report was found to be “the creation and escalation of a chain of rumors, with the ultimate result being the reporting of an accident that did not occur.”1 Researchers have attempted to replicate these conditions and fuse a contact lens to the cornea but have never succeeded.3 When contact lenses are heated, they experience a temperature increase that is more marked as the lens thickness increases. However, the temperature increase is not nearly high enough to cause a contact lens to fuse to the cornea without violating basic physical principles of matter.3 Heat is dissipated in a contact lens either by conduction, convection, or radiation. Studies have found that any heat generated “from a welding arc or electrical spark is not intense enough to dry up the eye’s fluid, nor could a contact lens concentrate rays to intensify the heat.”3,8 Only a radiation injury from not wearing proper ultraviolet (UV) protection could provide the extremely high energy levels that are required for contact lens corneal fusion. Although the welder’s injuries were similar to those of a radiation burn, he was wearing proper UV protection, so that was unlikely. Also, radiation damage would have caused an immediate onset of symptoms that would not have appeared 12 to 17 hours after the accident. Based on these and other similar findings, the Contact Lens Association of Ophthalmologists3 in a 1983 policy statement stated that contact lens wear does not increase the risk of ocular damage while arc welding. In spite of the overwhelming evidence refuting the contact lens corneal fusion theory, it still has proponents who believe that the arc flash creates microwaves that instantly evaporates the tear film and causes the contact lens to fuse to the cornea, resulting in permanent vision loss upon removal of the contact lens.2 Research has found that arc flashes are not capable of creating microwaves that possess enough energy to instantly evaporate the tear layer.9 In
597 addition, because of the thermal response produced in the tissue by microwaves,4 it would be impossible to have enough microwave energy to instantaneously evaporate the tear film and fuse a contact lens to the eye and yet spare the worker from receiving severe burns to the body. In fact, if such a scenario was possible, the worker would be instantly “cooked” and would not survive the accident. Another contact lens myth was popularized by a respected industrial ophthalmologist in the 1960s. He published another undocumented accident about an engineer who was wearing contact lenses and safety goggles and was splashed with a 50% caustic solution.5 Supposedly, this highly caustic solution was rinsed off his face, but the victim sustained severe corneal chemical burns. The ophthalmologist reported that the engineer’s contact lenses were responsible for the vision loss because they prevented the solution from being completely rinsed from his eyes before it caused severe ocular injuries.5 However, blaming these injuries on the contact lenses is difficult because properly worn safety goggles will easily prevent splashed chemicals from reaching the eyes. Based on the description of the accident, it is much more likely that safety goggles were either never worn or were not protecting the worker’s eyes when the accident occurred. Workers have a tendency to ignore PPE requirements unless their compliance is monitored and enforced. The Bureau of Labor reports that as many as 60% of workers who have suffered workplace ocular injuries were not wearing their ocular PPE at the time of the accident.3 In fact, 90% of all eye injuries could have been prevented had the individual taken the necessary safety precautions.10
The negative effect of the myths on contact lens use in industrial and chemical environments Industrial accidents are always considered newsworthy, and these supposed contact lens accidents are no exception. Media outlets continually resurrect and sensationalize these reports every few years even though they have been conclusively disproved. More importantly, these reports still continue to adversely influence industrial and chemical companies’ contact lens wear policies. Although there are instances in which contact lenses have contributed to or worsened an injury, Messana2 reports that contact lenses have been shown to either reduce or completely prevent injury 97% of the time. In fact, for every worker whose ocular injuries have been worsened by contact lens wear, there are nearly 30 other workers who were exposed to similar circumstances but whose contact lenses either prevented injury or did not increase its severity.2 Messana’s opinions have been supported by the federal government as well as by chemical and medical professional associations. In its PPE Final Rule, the Occupational Safety and Health Administration (OSHA) stated that “con-
598 tact lenses do not pose additional hazards to the wearer and additional regulation is unnecessary.”2 In addition to OSHA’s approval, the American Chemical Society’s (ACS) Committee on Chemical Safety and the American Optometric Association (AOA) have released position statements that address contact lens wear in the workplace. The ACS committee has stated that in many workplaces that handle hazardous chemicals, workers are “prohibited or discouraged” from wearing contact lenses as a result of “earlier statements based on rumors and perceived risks,” which has been proven to be unfounded.2 Realizing that contact lenses have either reduced or completely eliminated injury in a wide variety of workplace situations, they recommended that employers should permit contact lens wear in most workplace areas as long as those who wear contact lenses, wear the same PPE required of other workers.2 The AOA’s statement supported this decision and also refuted some of the common misconceptions that contact lenses negate the protection provided by safety equipment or make the cornea more susceptible to damage by optical radiation.2 They concluded by emphasizing that workplace contact lens wearing regulations must not be “based on perceived hazards, random experience, isolated unverified case histories, or unsubstantiated personal opinions.”2 In spite of these opinions from OSHA and the scientific and optometric communities, confusion over the safety of contact lenses is still common in industrial and chemical workplaces. In a 1994 survey of academic institutions that examined contact lens wear policies in chemical environments, Segal5 found that only 57% of the 26 responding institutions allowed contact lens wear. Three years later in 1997, Segal5 repeated the survey to determine if academic institutions had modified their safety policies in response to current research that supported the use of contact lenses when combined with standard PPE requirements. This time, besides only examining the contact lens polices of academic institutions, Segal expanded her survey to compare the contact lens wear and safety policies of industrial and chemical companies with that of academia. She found that although 77% of the 26 responding academic institutions now permitted contact lens wear, only 58% of the 26 responding industrial and chemical companies allowed contact lenses. This highlights the tendency of academic institutions to be more aware and accepting of current research, whereas industry reacts more slowly and cautiously to change unless significant financial savings justify revising their outdated yet effective safety practices.
Ocular protective benefits In 1974, Rengstorff and Black11 examined 128 documented industrial accidents that resulted in ocular injury, physical trauma, or hazardous exposure in contact lens wearers. These injuries ranged from exposure to chemical splashes and fumes to assorted metal foreign bodies and projectiles.
Optometry, Vol 78, No 11, November 2007 The authors concluded that although the contact lenses often were severely damaged, they consistently prevented or lessened the resultant injury to the cornea and other ocular structures. When combined with appropriate PPE, the contact lens provided additional protection for workers in many common industrial and chemical workplace conditions by providing protection and limiting damage from chemicals, fumes and vapors, trauma, foreign bodies, and environmental extremes.
Protection against chemical exposure The first protective benefit of contact lenses is that they provide varying levels of additional eye protection against acidic and alkaline chemical solutions. When working with chemicals, it is always critical that workers utilize proper PPE and follow standard safety precautions. However, if workers are noncompliant with their PPE, contact lenses will provide protection that would not be afforded to non– lens wearers. Research has found that although contact lenses absorb chemicals and vapors, it is unlikely that these substances would diffuse completely through the lens to reach the anterior surface of the cornea.2 In fact, this absorption process assists in protecting the cornea by allowing the contact lens to absorb some of the offending chemicals and thus decrease both the amount and time of chemical ocular exposure. This greatly reduces the severity of a resulting ocular injury as well as limiting the possibility of visual acuity loss. When working with highly concentrated corrosive acidic and alkali solutions, contact lenses provide little to no protection. These solutions are so corrosive that the protective barrier formed by the contact lens is penetrated quickly, such that a worker wearing contact lenses without PPE will suffer severe injury if the chemical is not immediately removed. Working with alkaline solutions requires the most caution, because they are more corrosive than an acid of equivalent strength and are thus able to penetrate tissue faster than acids, causing a more severe injury in a shorter amount of time. A 1982 study by Nilsson and Andersson12 found that contact lenses do not provide any protection against caustic solutions above 20%, although contact lens usage does not worsen the resulting injury as has been commonly believed. Inasmuch as acids have a slower penetration time, contact lenses provide a protective shield over the cornea that either prevents or reduces the possibility of ocular injury. This protective effect only lasts for a short period and is dependent on the acidic concentration, exposure time, and contact lens thickness, but has been shown to significantly limit or prevent ocular injuries. Nilsson and Andersson12 also found that when high plus hydrogel contact lenses are exposed to hydrochloride concentrations ranging from 20%, the resultant corneal damage is decreased by 75%. Although proper PPE must always be used when working with chemicals, in most instances contact lenses provide protection that could make the difference
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between a worker being blinded or saving that worker’s vision. In industry, conventional wisdom has always dictated that in the event of an accident, contact lenses would not be able to be quickly removed from the victim’s eye and would interfere with emergency eye irrigation. The fear was that the chemical would become trapped underneath the contact lens where it could not be rinsed away. However, when the eye is aggravated by a foreign body, chemicals, or a pain response, the lid blepharospasm reflex immediately forces the eye tightly shut. This happens so quickly that the contact lens is temporarily suctioned to the eye and the tears between the cornea and posterior surface of the contact lens create a barrier that prevents the chemical from getting to the cornea, reducing the severity of corneal damage.9,13 Blais10 reports that several researchers have found that contact lenses do not interfere with ocular irrigation, because the contact lenses are frequently flushed out. This occurs because the initially tight seal between the contact lens and the cornea weakens and allows the irrigating solution to flow easily underneath the lens to rinse away the contaminant and flush out the contact lens during irrigation of the eye. Blais10 states that “eyes with contact lenses and proper irrigation can be saved regardless of whether the lenses are removed during or after irrigation.”
Protection from chemical fumes and vapors Another concern associated with working with chemicals is the fumes and vapors that result from routine laboratory procedures. Although all chemistry laboratories utilize fume hoods for working with noxious chemicals, usually residual vapors are present in the laboratory. For years, contact lens wear was contraindicated when working with all vapors, but it is now known that vapors actually have varying effects on contact lenses. For example, a 1985 Italian study discovered that isopropyl and ethyl alcohol vapors penetrate hydrophilic lenses where they are absorbed and later leased into the wearer’s tear film.5 Similarly, a 1978 OSHA report recommended that contact lenses not be used “when working with acrylonitrile, 1,2 dibromo-3-chloropropane, ethylene oxide, methylene chloride, and 4,4-methylene dianiline chemicals.”7,14 However, studies have also found that when exposed to certain other vapors, contact lenses can provide additional protection. Nilsson and Andersson12 found hydrogel contact lenses decreased the exposure to trichloro-
Table 1 lenses
Ocular chemical protection provided by contact
Reduce or eliminate injury from exposure to acidic chemical solutions. Reduce or eliminate injury from exposure to alkaline chemical solutions of 20% and below. Reduce or eliminate ocular exposure from many fumes and vapors.
599 ethylene and xylenne vapors when compared with the exposure found in a non– contact lens–wearing eye. A similar study conducted by the Ophthalmology Department at the University of Nebraska tested the absorption of acetone, diethyl ether, trichloroethylene, and toluene in contact lenses and found that contact lens wearers exhibited decreased ocular exposure when exposed to volatile organic solvents.5 Other examples of contact lenses protecting against vapors have been observed. When soft contact lens wearers cut onions, they do not experience the “excessive tearing” that affects non–lens wearers. The soft contact lenses absorb and thus protect against the tearing stimulating allyl dissulfides that are released into the air when the onion is cut.5 A similar protective effect against tear gas has been documented by Dutch police authorities who do not require their soft contact lens wearing officers to wear gas masks when using tear gas. Aalphen15 found that when soft contact lens wearers are exposed to high concentrations of tear gas in a gas chamber, they were able to see clearly upon leaving the chamber and suffered no other physical signs of discomfort other than slight conjunctival injection. However, non– contact lens–wearing officers without a gas mask were only able to endure the chamber for a maximum of 2 minutes and could not open their eyes for, at most, 1 minute after leaving the chamber. Additionally, they also experienced nausea and vomiting and exhibited mild epithelial corneal staining.15 Aalphen15 concluded that the officers in the study who wore the soft contact lenses “kept their eyes open more easily and had quicker and better orientation.” This significantly improves their ability to use tear gas in riot control situations and eliminates the possibility that officers will become incapacitated by the gas if their gas mask is either dislodged or damaged (see Table 1).
Protection from mechanical trauma, foreign bodies, and particles Besides providing additional eye protection against chemicals and vapors, both hard and soft contact lenses have been found to provide varying levels of protection against mechanical trauma such as contusions, concussions, particles, and foreign body injuries. Contusion and concussion injuries are closely related, because often a contusion may also result in a concussive injury. Contact lenses are able to decrease some of the severity of a contusion by absorbing energy, which helps decrease the chance of a contra-coup injury, a retinal detachment, or another form of traumarelated retinal damage.4,11,16 How do rigid and soft contact lenses provide protection against blunt trauma, foreign bodies, and projectiles? Cases have been reported in literature in which hard lenses fractured after sustaining blunt trauma from field hockey sticks, fists, and other objects, yet the incident resulted in minimal or no corneal damage.4,11 Rigid lenses provide a physically hard barrier that acts as a shield that deflects a blow to the cornea. In a study by Chou et al.,16 an air gun fired
600 pulverized iron fillings into the eyes of pig cadavers wearing either rigid gas-permeable contact lenses or soft contact lenses. With rigid gas-permeable contact lenses, the only damage that occurred was to the exposed corneal surface not covered by the lens. Although hard lenses provide effective protection against blunt trauma and some small high-speed particles, they provide little protection against large sharp high-speed particles and dust and can trap small foreign bodies underneath the lens.4 Cullen4 reports that a 1981 study found that hard lenses were more likely to shatter and cause corneal damage from the lens shards when hit by large sharp projectiles as opposed to other types of contact lenses. However, in this study, the air gun and projectile were fired only 6 mm from the cornea and the majority of the projectile remained in the barrel of the air gun. This provided a constant force on the contact lens and did not allow the particles to be deflected at impact. Although this accurately measures the force needed to break a hard lens, it is extremely unlikely that this type of trauma would occur outside the controlled environment of the laboratory. Because of the fit of a hard lens on the cornea, it is susceptible to dust and particles in the tear film and on the conjunctiva, which can work their way behind the hard lens. Although these findings would seem to indicate that hard lenses are contraindicated in workplace conditions in which dust and particle exposure is likely, this is not necessarily true. Nichols and Good3 recommend that “with proper eye and face protection . . . hard contact lens wear should not create an additional hazard around flying particles.” However, they cautioned that workers “should wear rigid contact lenses with caution when working around dust and smoke particles because the particles’ entry behind the lens could visually incapacitate workers and place them at risk of further injury.”3 Like hard lenses, soft lenses can provide protection that varies depending on the type of foreign body and the thickness, rigidity, and water content of the lens.4 Lowwater soft contact lenses provide a protective benefit by absorbing some of the impact and lessening the blow the eye receives when struck by a foreign body. This occurs because the design of the soft contact lens greatly increases the necessary energy needed by a foreign body to perforate the contact lens and cornea. Chou et al.16 found that pig eyes fitted with soft contact lenses were well protected, because only 3 of 11 eyes received a mild corneal abrasion, whereas all 11 control eyes without soft contact lenses had severe corneal damage. However, unlike the hard lenses, nearly every soft lens was destroyed by the testing. Cullen4 reports that in a 1981 Nilsson study high-water soft lenses did not provide protection from high-speed large sharp particles, whereas low-water soft lenses provided significant protection against the ability of a foreign body to penetrate the contact lens and cornea. Cullen4 states “while foreign bodies may be trapped beneath rigid lenses, this does not happen with hydrogel lenses unless the speck is inserted with the lens.” During
Optometry, Vol 78, No 11, November 2007 Table 2 Corneal protection provided by contact lenses against physical hazards Mechanical trauma Foreign bodies Particles Temperature extremes High winds
Operation Desert Storm, pilots reported that their soft contact lenses adapted well to the dry sandy desert conditions and that they did not experience discomfort or foreign body sensations.9 The larger size and tighter fit of the soft contact lens prevents particles from getting underneath the lens and protects the wearer from particles that would otherwise cause discomfort, tearing, and decreased vision.
Protection from cold temperature extremes and high winds The last protective benefit of contact lenses is the protection they provide from physical and environmental hazards. Compared with a rigid lens, the larger diameter of soft contact lens provides a greater area of corneal coverage and helps to protect limbal stem cells.3 Protection of these cells is vital inasmuch as it ensures that the corneal epithelial layer is able to regenerate when abraded or damaged. However, one study for the United States Navy found that smaller rigid lenses can provide similar protection. This study exposed rabbits to temperatures of ⫺28.9°C and 125 mph winds for several hours while wearing rigid hard lenses. The rabbit subjects suffered only minimal ocular damage and Socks17 concluded that “contact lenses may be acceptable and may even offer protection to the eyes from wind-driven ice and snow in cold environments” (see Table 2).
Increased workplace performance and visual comfort Increased field of view and decreased distortions In addition to providing ocular protection, contact lenses provide many specific visual benefits such as a wider field of view, reduced aberrations, and freedom from the inherent restrictions that accompany spectacle wear. One of the most important benefits provided by contact lenses is that the visual field of a contact lens wearer is only limited by the field of fixation compared with the limits caused by the size of the spectacle lenses and frame.18 Unlike spectacles, contact lenses move with the eye and allow the wearer to always look through the optical center of the contact lens, maximizing visual acuity and field of view. However, with spectacles, wearers are forced to move their heads to see objects that fall outside the field of view provided by the
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glasses. Compounding this problem is that spectacle lenses, according to Preuss, create prismatic distortions that reduce the visual field in spectacle wearers with higher refractive errors.6 These distortions are caused whenever the wearer looks into the lens periphery and away from the optical center of the lens.
Reduced aberrations, reflections, and glare Spectacle lenses are not perfect optical systems and thus are subject to various aberrations that can decrease vision and cause visual discomfort. Although some aberrations are minor and have little impact, 3 specific aberrations, oblique astigmatism, distortion, and curvature of field, all decrease the quality of vision through spectacle lenses, especially in prescriptions with high refractive errors. These aberrations all occur to varying degrees when looking through the periphery of a spectacle lens.19 However, with contact lenses, the wearer only looks through the optical center of the lens and not through the periphery, eliminating oblique astigmatism and curvature of field. Distortion, which is also affected by the distance between the spectacle lens and pupil, as well as the power of the peripheral lens, is minimized by the contact lens sitting directly on the eye.18 This is why contact lens wearers typically can see better with contacts than they can with glasses; the optical aberrations present in spectacles are either minimized or completely eliminated. Another visual benefit provided by contact lenses is that they are not subject to the annoying reflections and glare that can be caused by spectacle lenses and frames. Reflections and glare result whenever light is incident upon 2 surfaces with different refractive indices and are created when light enters from either the front or the back surface of the lens. Optically, the design of spectacle lenses creates 5 specific types of reflections. Of these, 3 result from reflections produced by light entering in front of the spectacle lens and being reflected back between the cornea and the front and back surfaces of the lens. Similarly, the other 2 result from light entering from behind the spectacle lens and reflecting off the front and back surface of the lens. However, once a contact lens is placed on an eye, light is unable to enter behind the lens, and 2 sources of glare are immediately eliminated.18 Additionally, reflections and glare increase in larger spectacle lenses, where increasing the lens surface area degrades its optical properties. However, with the greatly reduced lens surface area of contact lenses, these reflections are minimized and usually not observed by the contact lens wearer, resulting in a corresponding visual acuity improvement. Although antireflective coatings may be used with spectacle lenses, they are only able to eliminate glare from certain wavelengths of light, and the coating attracts dust, making them difficult to keep clean, especially in dirty workplace environments. For spectacle wearers who tend to scratch their lenses or are exposed to solvents and particles that can damage the antireflective coating, they will experience problems with glare and halos that will in most cases cause them to report decreased vision and increased discomfort.
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Visual freedom from spectacles Contact lenses provide workers with other significant benefits, such as complete freedom from reliance on spectacle lenses. No longer will they need to worry about having their spectacles knocked off, finding themselves unable to safely perform their duties. Furthermore, if their spectacles were knocked off or broken, many workers might be unable to see clearly enough to finish their task and could become a safety hazard not only to themselves but to those around them as well. Although it is possible that a contact lens could become dislodged, it rarely happens and is especially unusual with soft contact lenses. However, even if a contact lens was dislodged, the binocular worker would still be able to see clearly with the other eye, and would be much more likely to be able to either complete or stop a current task without self harming or to others. A survey by Good and Augsburger20 found that approximately 52% of police officers have had their glasses dislodged while on duty. Contact lenses essentially eliminate this risk inasmuch as once they are in the eyes, they are unable to be broken, are extremely difficult to dislodge, and provide consistently clear vision in a wide variety of circumstances.
Safety benefits for respirator use The importance of workplace spectacle lens freedom has been highlighted by efforts firefighters made to reverse a longstanding OSHA decision that banned contact lens use while using full-faceplate respirators. Contact lenses were originally banned because it was believed that users faced an increased risk of either being visually incapacitated by dust from their air supply being blown under their contact lenses or by having a contact lens become dislodged, block the mask’s air flow, and suffocate the wearer.8 However, after discovering that contact lenses provided a wider field of view and ensured an airtight seal between the mask and wearer’s face, firefighters ignored the ruling and used them without any ill effects. After all, comfortably wearing spectacles underneath the faceplate of a respirator is difficult, as some frame shapes and styles prevent the respirator masks from creating a proper seal, inadvertently exposing wearers to environmental hazards from which they are trying to protect themselves.7 In 1995, after preliminary surveys reported improved performance and safety, OSHA funded a study to reexamine the previous 1969 decision. This study confirmed the 1995 survey results, so OSHA concluded that “contact lenses do not pose additional hazards to the wearer, and has determined that additional regulation addressing the use of contact lenses is unnecessary” and approved contact lenses for respirator use.21
Environmental vision benefits and UV protection Contact lenses offer protection against environmental changes and fluctuations that decrease vision. According to Good and Augsburger,20 56% of spectacle-wearing police
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Table 3 Visual workplace benefits of contact lenses over spectacle lenses Increased field of view. Reduced optical aberrations and distortions. Increased safety when used with appropriate PPE. Vision not affected by rain, fog, or snow. Improved confidence and self-image.
Improved visual acuity. Reduced reflections and glare. Freedom from spectacle dependency. Difficult to dislodge. Improved cosmesis.
officers have had to remove their glasses when rain, fog, or snow blurs or distorts their vision. This decreases the safety and efficiency of workers, especially outdoor workers, whose glasses and consequently vision are negatively affected by environmental changes. Today, contact lenses are available that block UV radiation and help protect the cornea, lens, and parts of the conjunctiva. UV rays have been implicated in cataract formation, so UV-blocking contact lenses help protect the crystalline lens from irreversible cumulative damage, which is not only caused by sunlight, but by popular fluorescent lighting as well.
Social and psychological benefits of contact lens wear The final benefit of contact lenses is the resulting visual freedom the lenses provide, enhancing the psychological, emotional, and physical functioning of the worker in the workplace. Once people begin to wear contact lenses and realize how much vision can be improved, they do not want to have to return to spectacle wear again. Cullen22 said that “most successful contact lens wearers wish to wear their contact lenses in all aspects of their lives, including the workplace.” It has been found that the use of contact lenses helps improve workplace communication (besides improving cosmesis); some workers feel that their eyes are hidden by their spectacles and believe that their communication abilities are better without them. This is especially true when the spectacle lens is noticeably thick or if it magnifies or minifies the wearer’s eyes.18 Better cosmesis increases worker confidence, self-esteem, and communication ability and improves workplace performance (see Table 3).
Precautions and contraindications for workplace contact lens wear Chemical vapors Contact lens wear is not recommended when working with acrylonitrile; 1,2 dibromo-3-chloropropane; ethylene oxide; methylene chloride; 4,4-methylene dianiline; or isopropyl
and ethyl alcohol vapors.5,7,14 The preamble to OSHA’s guidelines does not include the specific basis for their recommendation, but it is likely based on the potential for the contact lens to absorb the vapor and release it into the tear film.23 This occurrence would be minimized by fitting workers who work with these chemicals with daily disposable contact lenses, which would ensure that any residual vapor in the lens would not be in contact with the eye for a significant amount of time. By combining goggle use (which would be required of contact lens wearers and non– contact lens wearers alike) with daily disposable lenses, contact lenses would likely be safe to wear in these environments.
High temperatures Some workplace environmental conditions can make successful contact lens wear difficult for certain workers, although they can still successfully wear contact lenses. Although studies have shown the minimal effect of extremely cold temperatures on corneal health, direct corneal contact with high-temperature objects will cause variable corneal damage that is dependent on the temperature and time of exposure.4,17 Hoffmann and Kunz24 found that a 1- or 2-minute direct corneal exposure of water heated to 47°C caused a mild superficial keratitis, whereas temperatures of 80°C resulted in corneal clouding and edema. Although worker exposure to these types of direct heat is unlikely, some workers, especially those who work with smelters, ovens, and furnaces, are routinely exposed to much hotter air temperatures. In fact, the air temperature in a typical sauna can reach between 80° to 100°C. Inasmuch as only the air temperature is elevated, no direct corneal damage is caused in this environment except for increased rate of tear film evaporation that dries out contact lenses and causes dry eye symptoms.4 This dryness can be treated by educating workers to increase their blink rate and having them use artificial tears or lubricating drops as needed during the workday.
The effects of high altitudes and low humidity Altitude-related contact lens problems may be especially difficult for aviation workers such as pilots, aircrew, stewardesses, and individuals who work at altitudes ranging from 4,000 to 9,144 meters. One study simulated an altitude of 9,144 meters and found that subjects using supplementary oxygen had no problems except for a few reporting “dry and tired” eyes.25 However, Castren et al.,26 when simulating a high-humidity environment at an altitude of 4,000 meters, reported that “corneal erosions and stromal opacities” were observed in subjects wearing contact lenses. Although these findings are important, the study is not particularly applicable inasmuch as aircraft travel creates a low-humidity environment rather than the high-humidity conditions created by Castren’s study. Additionally, in
Tyhurst et al
Literature Review
Table 4 Possible environmental workplace contraindications for contact lens wear High temperature environments High altitudes Low humidity Certain chemical vapors
1988, Flynn et al.27 reported that although corneal thickening increases at high altitudes, the small resultant myopic shift does not affect pilot vision, as a result of “13 years or more of experience of pilots in the Swedish and other air forces.” They concluded that hydrogel contact lenses may be worn safely while flying military aircraft. Once the humidity level falls below 11%, contact lenses begin to dry out, and the tear break up time begins to decrease. This decreases the lens radius of curvature, lens movement, and oxygen transmissibility and makes the lens more susceptible to deposits. Inasmuch as movement and tear exchange are critical for successful contact lens wear in these patients, practitioners fitting these workers must ensure that their lenses are not fit too tightly.4 Contact lens wearers will also benefit from a frequent replacement schedule, adding enzymatic cleaners to their cleaning regimen, and receiving instructions not to overwear their contact lenses. Additionally, Cullen4 reports that the newer highwater-content contact lenses have decreased both the incidence and severity of dryness symptoms that have always been caused by high altitude and low-humidity environments. Fitting these patients into high-water lenses maximizes ocular comfort and decreases or eliminates dry eye symptoms (see Table 4).
Patient education and lens fitting recommendations It is critical for practitioners to thoroughly educate workers who plan to wear contact lenses in industrial or chemical environments that, although their contact lenses do provide additional protective benefits, they are not PPE, and workplace standard PPE requirements along with general safety practices must always be followed. It is also recommended that workers who work with chemical agents be fitted with daily disposable contact lenses. These workers also must be educated about the importance of having a backup pair of spectacles at their workplace in case they ever experience discomfort, redness, irritation, or eye pain and need to remove their lenses.4 Finally, practitioners considering fitting gas-permeable lenses must ensure that workers are not placed in situations in which they can be visually incapacitated by a foreign body. Nichols and Good3 advise that workers must be able to “safely call timeout and easily cease operations to remove the contact lens and attend to the foreign body” that disrupts their vision. This is especially critical in environments that
603 are dirty, dusty, or windy.3 These environments cause gaspermeable lenses to have a higher incidence of foreign bodies becoming trapped behind the lens and disrupting vision. In hazardous workplace environments that involve welding, working at heights, some types of construction work, and operating heavy machinery or construction equipment, a sudden loss of vision can not only endanger the safety of the gas-permeable lens wearer but others as well. It is much less likely for soft contact lens wearers to become incapacitated by foreign bodies or particle matter than gas-permeable lens wearers, and thus soft contact lenses are recommended for these environments (see Table 5).
Discrimination against workplace contact lens wear and policy recommendations Workplaces that enforce outdated contact lens policies that either disqualify contact-lens-wearing workers from certain job positions or require contact lens wearers to use additional PPE not required of non– contact lens wearers, violate the Americans with Disabilities Act (ADA).5 Under this act, employers are not allowed to remove or reassign workers if the worker still can “perform the essential functions of the position with or without accommodation without substantial risk of threat to themselves or others.”5 Contact lenses for medical applications are an approved accommodation method except in the rare instances in which contact lenses have been conclusively proven that the lenses “pose a direct threat to the health and safety” of the worker or others.5 Blais1 concurs, stating that “there is no justification for employers to discriminate against employees who wear the visual accommodation required for them to perform their essential functions.” Employers who do so may be in violation of the ADA which is equivalent to denying a worker employment on account of age, race, or religion. Additionally, the ADA prohibits employers from requiring contact lens wearers to use PPE that is not required for non–lens wearers. Inasmuch as contact lenses have been shown to increase workplace safety, it is discriminatory to force contact lens wearers to use PPE they do not need and that non– contact lenses wearers do not have to use. This not only creates additional worker and company expenses, but may strain worker relationships and create problems and
Table 5
Workplace contact lens fitting pearls
Always educate all contact lens patients about the importance of wearing proper PPE. Fit workers who work around chemicals with daily disposable lenses. Recommend workers keep a backup pair of spectacles at their workplace. Fit patients exposed to dirty, dusty, or windy environments with a soft lens instead of a gas-permeable lens.
604 distractions that decrease employee performance and productivity. Workplace contact lens safety experts, the American College of Occupational and Environmental Medicine, the American Academy of Ophthalmology, and the American Optometric Association all recommend that industrial and chemical companies create written corporate contact lens policies.1,22,23 These policies should list the required jobspecific PPE, plant locations where PPE use is required, and whether contact lens wear is banned or limited in any particular work area. It is critical that these policies are flexible enough to evaluate individual worker needs on a case-by-case basis to ensure that they are provided with a refractive correction that maximizes their vision and ocular safety. If industrial and chemical workplaces already have established written contact lens policies, they must be reviewed to ensure that they are current and recognize the safety of workplace contact lens use. Additionally, companies must verify that their policies comply with the ADA by ensuring that all contact lens wearers are not discriminated against, regardless of why they wear them. Finally, all policies should highlight how contact lenses, when worn with standard PPE, are safer than spectacles in most workplace situations, because not only do they provide physical protection against environmental hazards, they also provide several other visual benefits that improve visual comfort and attitude and contribute to increasing employee satisfaction and productivity.
References 1. Blais BR. Discrimination against contact lens wearers. J Occup Environ Med 1998;40:876-80. 2. Messana K. The last word on contacts. Occup Health Saf 2001;70: 68-70. 3. Nichols JJ, Good GW. Contact lenses and the work environment [Contact Lens Spectrum Web site]. November 2003. Available at http://www.clspectrum.com. Last accessed March 14, 2005. 4. Cullen AP. The environment. In: Bennett ES, Weissman BA. Clinical contact lens practice. Philadelphia, PA: J.B. Lippincott; 1991:1-28. 5. Segal EB. Contact lenses and chemicals. Chem Health Safety 1997; 4:33-7. 6. Preuss A. The world of contact lenses. Chem Health Safety 1995;2: 12-5.
Optometry, Vol 78, No 11, November 2007 7. American College of Occupational and Environmental Medicine. The use of contact lenses in an industrial environment [ACOEM Web site]. May 2003. Available at http://www.acoem.org. Last accessed March 14, 2005. 8. Segal EB. Contact lenses and chemicals: An update. Chem Health Safety 1995;2:16-21. 9. Blais BR. Does wearing of contact lenses in the workplace post a direct threat. The Occupational and Environmental Medicine Report 1998;12(3):17-31. 10. Blais BR. Contact lenses in industry: The ongoing discussion. Chem Health Safety 1997;4:22-6. 11. Rengstorff RH, Black CJ. Eye protection from contact lenses. J Am Optom Assoc 1974;45:270-6. 12. Nilsson SEG, Andersson L. The use of contact lenses in environments with organic solvents, acids, or alkalis. Acta Ophthalmologica 1982; 60:599-608. 13. Petreycik RM. Contact lenses in the workplace: more than meets the eye. Safety and Health 1997;155:74-7. 14. Code of Federal Regulations-Parts 1900 to 1910 Personal Protective Equipment. 29 CF2R 1910.I32. Revised 1994. 15. Aalphen CC. Protection of the police against tear gas with soft lenses. Mil Med 1985;150(8):451-3. 16. Chou B, Ritzmann E, Anthony P. Ocular protection by contact lenses from mechanical trauma. International Contact Lens Clinic 1992; July/August:162-6. 17. Socks J. Contacts lenses in extreme cold environments: response of rabbit corneas. Am J Optom Physiol Optics 1982;59:297-300. 18. Fannin TE, Grosvenor T. Optics of contact lenses. In Fannin TE, Grosvenor T, eds. Clinical Optics. Boston, MA: Butterworth-Heinemann: 1996:196-203, 373-405. 19. Pedrotti LS, Pedrotti FL. Optics and Vision. Upper Saddle River, NJ: Prentice-Hall; 1998:122-39. 20. Good GW, Augsberger AR. Uncorrected visual acuity standards for police applicants. J Police Sci Admin 1987;15:18-23. 21. Code of Federal Regulations-Parts 1910 and 1926 Respiratory protection final rule. Fed Reg. Vol. 63. no 5, Thursday, January 5, 1998 Rules and Regulations, pp 1162. 22. Cullen AP. American Optometric Association guidelines for the use of contact lenses in the industrial environments. In: Good GW, Stephens GL, Pitts DG, et al, eds. American Optometric Association Occupational Vision Manual. St. Louis, MO: AOA, 2002;23-4. 23. Schulte P, Ahlers H, Jackson L, et al. Current Intelligence Bulletin 59: Contact lens use in a chemical environment. National Institute for Occupational Safety and Health 2005;1-3. 24. Hoffmann W, Kunz E. Uber Warmeschadigungen des Auges. Grasefes Arch Clin Exp Ophthalmol 1934;132:155-84. 25. Eng WG, Rasco JL, Marano JA. Low atmospheric pressure effects on wearing soft contact lenses. Aviat Space Environ Med 1978;49:73-5. 26. Castren J, Tuovinen E, Lansimies E, et al. Contact lenses in hypoxia. Acta Ophthalmologica 1985;63:439-42. 27. Flynn WJ, Miller RE, Tredici TJ, et al. Soft contact lens wear at altitude: effects of hypoxia. Aviat Space Environ Med 1988;59:44-8.