Laser Safety in Ophthalmology

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Overview

Light Amplification by Stimulated Emission of Radiation (LASER) therapy utilizes a highly specific and concentrated beam of light that can be used to alter tissues in the medical treatment of disease (i.e., medical grade lasers). Since the times of ancient civilizations who used sunlight to remedy skin diseases, the use of light in clinical therapy has continued to grow with modern technology and scientific knowledge to become what laser treatment is now today.[1] Laser is utilized in procedures of almost all medical fields (e.g., dermatology, cardiology, oncology, neurosurgery, plastic surgery, general surgery, etc.).[2][3] In particular, laser use has become especially emphasized in the field of ophthalmology due to the eye’s innate transparent and focusing properties as an optical device. Just as it facilitates the transmission of natural light, the transparent cornea and media also allow laser light to reach and affect almost all tissues of the eye.[4] The efficacy and safety of specific low energy lasers combined with minimal invasiveness make laser an ideal modality for both diagnostic imaging and clinical treatment of eye pathology.[3][5][6][7]In fact, its ease of use allows it to be performed in a variety of outpatient settings.

Lasers are now so commonplace that it can cause complacency. However, there are risks to the eye accompanied with laser use. Laser surgery is still a form of surgery, and its risk profile must be adequately assessed as such. Furthermore, safety guidelines and complications unique to lasers must also be taken into careful consideration. Similarly, the use of lasers in non-medical contexts requires a need for understanding of the impact that can be had on the eyes, as these situations can often be much less regulated.

Background

Light is released when excited electrons return to their original energy levels and emit photons of electromagnetic energy. Laser light is differentiated from other light sources (such as sunlight or a light bulb) due to several specific properties. Laser beams are typically monochromatic (single wavelength) and collimated (parallel light rays). Most importantly, lasers are coherent (the electromagnetic waves are in phase with each other in both space and time).[5] The light is amplified by stimulated emission of radiation (i.e., LASER). The combination of these characteristics distinct to lasers is critical for its precise and powerful application.

Medical Laser Exposure

A laser beam’s parameters may be adjusted based on intended use and the target. Each wavelength and power setting in laser can be chosen based on the delivery system, procedure, and type of tissue or pathology that is to be treated.[3][5] For example, an infrared diode laser (at a wavelength of 806-810nm) may be used for retinal photocoagulation while an ultraviolet excimer laser (at 193 nm) may be used for corneal reshaping. Ophthalmic lasers have different tissue parameters that allow them to exert a wide variety of beneficial clinical effects on ocular tissue (e.g., photoablation, photocoagulation, fragmentation, or perforation).[2] These same beneficial effects of laser therapy, however, can result in risk of ocular damage.

In the clinic, ophthalmic lasers are often directly controlled by the operator surgeon (typically via a foot pedal control). The intended energy burst then travels along a fiber optic cable to a device that transforms and transmits the collimated laser beam to the target. Lasers may also have a second reference targeting laser beam in order for the treating surgeon to visualize where the treating laser beam energy will land. Just as the type of laser varies, the device for delivery can also change. In ophthalmology, laser delivery devices include slit lamps, operating microscopes, intraocular probes, and indirect ophthalmoscopes.[5][8]

Non-medical Laser Exposure

Apart from their therapeutic applications, lasers are also employed in community, laboratory, industrial, and military settings.[9][10]

In the community setting, lasers can be easily accessed in a variety of forms (e.g., laser pointers, laser scanners, laser projectors). Community-acquired laser injuries are normally transient and less severe as commercially available lasers are less potent.

In the laboratory and industrial settings, lasers are used for research and manufacturing (e.g., cutting, welding) purposes. Laboratory and industry-acquired laser injuries are more severe due to the intensity of lasers used in these settings. Such laser injuries are preventable and almost always occur when there is failure to comply with equipment operation guidelines or eye safety regulations.

Military lasers are widely applied in security, tactical, communication, and other military systems. The use of lasers as weapons to cause permanent blindless is strictly prohibited by the Geneva Conventions and the United Nations’ 1995 Protocol on Blinding Laser Weapons. However, laser eye injuries are still present in the military setting often due to accidental exposure or unintended use.

It is important to note that laser injuries in almost all settings are likely underreported because of potential legal consequences for protocol violations and perhaps military restrictions.[9][10]

Even though community and commercially available lasers have limited hazard potential, they can still engender adverse outcomes when used inappropriately. In the United States, it is illegal to aim a laser pointer at an aircraft or its path. This prohibition is due to the distraction, temporary visual disturbance, and view obstruction to the pilot -- not because of harm to their eyes. Even the most potent and hazardous Class IV lasers are unlikely to cause eye injury due to the great distance and layers of environmental barriers between an aircraft and the ground.[11]

Similar distracting and temporarily restricting uses of laser can also be found at public protests and demonstrations. Deliberately aiming a laser into the eyes of either protestors or police would be inappropriate operation of a laser device. However, even at very close proximity, such action would still likely not result in permanent eye injury. Owing to body movements as well as aversion reflexes, the conscious individual would not remain still long enough for a laser to inflict irreversible damage.[12]

Compared to medical lasers, less potent non-medical lasers do not cause the same severity of ocular injury. Nevertheless, it is imperative that proper use guidelines and restrictions are followed in order to maintain safety and well-being.

Hazard Risk

Medical use of lasers in surgery constitutes a form of bladeless surgery, and it carries some of the corresponding risks and potential complications associated with conventional blade cutting surgery. According to the U.S. Food and Drug Administration (FDA), these include, “incomplete treatment, pain, infection, bleeding, scarring, and skin color changes.”[6]

Laser therapy however also introduces additional and unique risks. The FDA categorizes all manufactured laser products into four major hazard classes labeled Class I to IV. Class I lasers are non-hazardous (e.g., laser printers and DVD players); Class II lasers are low hazard but only when viewed directly for long periods of time (e.g., bar code scanners); Class III lasers are potentially significantly hazardous to eyes with direct viewing (e.g., laser pointers); and Class IV lasers are significantly hazardous to eyes and skin (e.g., research and medical lasers).[13]

Reflected Beams

The most frequent cause of accidental laser ocular exposure is reflected beams.[7] Class IV lasers are significantly hazardous because these reflected beams pose considerable exposure risk and ocular protection is required.[13] Light reflects off flat, specular (mirror-like) surfaces, and many pieces of equipment in the operating room are made of such material. Surfaces closest to the lasers, such as surgical instruments and delivery devices, are often metallic and reflective. Reflection can also occur from the patient’s cornea or contact lenses used in surgery.[7] It is important to note that some ophthalmic lasers extend into the ultraviolet and infrared wavelengths, making the reflected beams not visible to the human eye and thus the risk may be difficult to detect.

Hazard Zones

Due to its limited divergence, laser light remains concentrated even at further distances. This makes the Nominal Hazard Zone (NHZ), or the area where direct, reflected, or scattered beams could cause adverse effects, more expansive and difficult to predict.[7][13]

Reduced Reflexes

The corneal blink reflex causes an individual to involuntarily close their eyelids following sensory stimulation to the cornea. This unconditioned reflex response is a protective mechanism used to shield the individual from unwanted irritants (e.g., bright lights or noxious chemicals) and typically is sufficient to protect against most long duration low hazard laser exposure.[14] Under anesthesia however, a patient’s blink reflex is greatly diminished or completely abolished and continues to be absent for hours, even after the return of consciousness and ability to blink on command.[15] While bright sunlight would already warrant a blink response, laser light can be millions of times more radiant than the sun. A patient under surgical anesthesia would be unable to perform the normal aversion response to protect their eye from intense heat or light produced by laser.[7]

Focused Light

Structures of the eye function to focus light onto the retina in order to produce images for vision. Likewise, the eye can also focus laser beams to concentrated areas on the retina, adversely resulting in inadvertent laser burns.[13]

Fire Hazards

Class IV lasers as well as their reflected beams present fire hazards.[13] Accidentally misfired, stray, and reflected beams can ignite surgical drapes, causing serious heat injuries to patients and others in the treatment area.[7]

Clinical Presentation

Laser injury, whether from medical or commercial lasers, can result in considerable legal, ethical, financial, and medical consequences.[16] Thus, it is important for ophthalmologists to be able to distinguish true laser injury from other underlying problems.[17]

Signs and Symptoms

Laser injury may be unilateral or asymmetric and bilateral depending on the type and duration of laser exposure.[17][18] Patients with acute exposure to a high-density laser may complain of seeing a bright flash of light (even if the laser wavelength is not in the visible light spectrum) followed by loss of visual acuity in phototoxicity. Patients with a laser injury may complain of transient ocular pain or headache, a visual scotoma, photophobia, metamorphopsia, or dyschromatopsia. Chronic pain, redness, or irritation of the eyes, face, or head are typically not attributable to laser injury and may suggest another underlying problem.[16][19]

Physical Examination

Typical examination findings of laser phototoxicity include tissue hemorrhage, perforation, or scarring.[17] Visual abnormalities and retinal lesions have been described in laser phototoxicity. In addition to careful dilated ophthalmoscopy, tissue injury may be better visualized and documented with ancillary imaging techniques including: adaptive optics scanning laser ophthalmoscope (AOSLO), fluorescein angiography (FA), fundus autofluorescence (FAF), and optical coherence tomography (OCT).[16][19]

  • Amsler grid abnormalities (e.g, metamorphopsis, central or paracentral scotoma) should be documented and may be more sensitive to focal or small areas of retinal injury than traditional automated perimetry which is designed to test the peripheral rather than central visual field.[17] Focal central testing of the visual field (e.g., 10-2 Humphrey visual field) may be more sensitive to the detection of occult scotomas in retinal phototoxicity.
  • OCT of the macular can show to the micron level areas of unsuspected phototoxicity. A laser-induced retinal lesion may show inner or outer retinal, retinal pigment epithelium (RPE), or choroidal level abnormalities including discontinuity or elevation, and/or a macular hole with increased reflectivity at base due to scarring.[16][17][19]
  • FA of a laser-induced retinal lesion may show linear streaking, and/or a hypofluorescent lesion with development of a hyperfluorescent RPE window defect over time.[16][17]

Ocular Findings[20][21][22]

Spectral Wavelength Laser Type Case Settings Ocular Findings
Visible (380-750nm) 450-480nm Blue lasers Commercial, Medical Retina:
  • Outer retinal layer defect
  • Full-thickness macular hole
  • Macular edema
  • Sub-internal limiting membrane hemorrhage
  • Epiretinal membrane
  • Subhyaloid hemorrhage
  • Subretinal fluid
  • Schisis-like cavity
480-520nm Blue-green lasers Military, Medical Retina:
  • Subhyaloid hemorrhage
520-536nm Green lasers Military, Industrial, Commercial, Medical Retina:
  • Outer retinal layer defect
  • Subretinal hemorrhage
  • Retinal pigment epithelium lesion, disruption, atrophy, and scarring
  • Chorioretinal scarring
  • Macular pigment clumping and loss
  • Foveal exudation
620nm Nd:YAG lasers Military, Medical Retina:
  • Macular hemorrhage
630-670nm Red lasers Commercial, Medical Retina:
  • Retinal pigment epithelium lesion, disruption, and atrophy
  • Choroidal neovascular membrane
  • Subretinal hemorrhage
694.3nm Ruby lasers Military, Medical Retina:
  • Subretinal hemorrhage

Vitreous:

  • Vitreous detachment
Infrared (750nm-1mm) 755nm Alexandrite lasers Commercial, Medical Conjunctiva:
  • Conjunctival hyperemia

Pupil:

  • Pupillary distortion

Anterior chamber / iris:

  • Anterior uveitis
  • Posterior synechiae
  • Iris inflammation and atrophy
800nm Diode lasers Industrial, Commercial, Medical Pupil:
  • Pupillary distortion

Lens:

  • Cataract formation

Anterior chamber/iris:

  • Iris atrophy
  • Posterior synechiae
  • Anterior uveitis

Visual field:

  • Visual field defect including scotoma
780-806nm Titanium-sapphire lasers Industrial, Medical Retina:
  • Full-thickness macular hole
1064nm Nd:YAG lasers Military, Industrial, Medical Cornea:
  • Corneal epithelial injury

Vitreous:

  • Vitreous hemorrhage

Retina:

  • Retinal pigment epithelium lesions
  • Macular hemorrhage
  • Full-thickness macular hole

Prognosis

The smaller and greater distance the lesion is from the fovea (which supplies the highest resolution central vision), the better the visual prognosis. In mild or focal ocular phototoxicity cases even when involving the macula, the visual acuity may significantly improve and stabilize over days to months. More severe, larger, or subfoveal lesions may however lead to permanent chorioretinal scarring. Macular hole, macular cyst, choroidal neovascularization, and preretinal membrane formation have all been reported however after laser injury.[17][18]

Management

There is no standardized protocol for the evaluation and treatment of laser-induced retinal injury.[17] Although intravenous and oral corticosteroids have been proposed to reduce the adverse cellular inflammatory responses (e.g., macular edema), but there are also potential treatment side effets.[18] Vascular endothelial growth factor (VEGF) inhibitors and photodynamic therapy may be helpful in treating choroidal neovascularization.[17][19] Surgery is typically not indicated, but some patients with unresolved complications (e.g., macular hole, epiretinal membrane) may benefit from surgical removal of scar tissue or hemorrhage.[18]

Laser Safety

In the United States, there are currently two general safety standards for medical application of lasers. The American National Standard for Safe Use of Lasers in Health Care, last updated in 2018, is a guide for safe use of lasers in health care (ANSI Z136.3).[9] It is a voluntary standard, but it is often referenced in establishing and reviewing medical laser safety policies. The other standard is the FDA’s Code of Federal Regulations, last updated in 2019, which has mandatory electronic product regulations for manufacturers of laser products (Title 21 – Food and Drugs, Subchapter J – Radiological Health).[10] This standard delineates the required certifications, labels, information, and directions for laser products.

Environment and Equipment Safety[5][7][23]

  • A laser device should only be operated by a qualified physician.
  • A laser device should not be operated if any abnormality or improper functioning is noticed.
  • Instructions and safety precautions should always be reviewed prior to operating a laser device.
  • Repair, calibration, and maintenance of laser devices should only be carried out by qualified technicians.
  • Equipment should be maintained and inspected including the fiber optic cables for safe operation.
  • Place a warning sign on the entrance to the treatment area in order to alert people of laser treatment in progress and prohibit entrance of unauthorized personnel.
  • Appropriate positioning of equipment is essential for minimizing accidental misfiring. This includes use of a standby switch, proper placement of foot pedal, and clear information regarding equipment placement to all personnel.
  • Remove all unnecessary reflective surfaces from the treatment area and substitute for non-reflective material whenever possible. Consider using black anodized surgical instruments in order to reduce reflection hazards. However, be aware that blackening of instruments may contrarily cause increased temperature and increased reflection for different wavelength lights (blackening causes more specular reflection of infrared light).
  • Consider using sandblasted and electropolished instruments in order to reduce heat conductance.
  • Moisten drapes as needed and be prepared to extinguish fires if necessary.

Patient Safety[8][23][24]

  • Protective shields should be worn during laser operation. A wide variety of different eye and face shields are available depending on the laser device and procedure. When using shields, it is important to make sure the shields are well-fitting and do not have sharp edges or scratches that could damage structures of the eye.
  • A complete and accurate patient history and physical exam are imperative. Some procedures and lasers have contraindications such as previous ocular surgery, trauma, presence of an intraocular lens, and certain anatomical features.

Physician Safety[5][7][23]

  • Physicians should be able to see the pointer laser beam for reference, but they need to be protected from the reflected treatment laser light. Safety filters installed within laser devices are an important barrier, allowing passage of the harmless pointer laser through to the physician’s eye while blocking harmful treatment lasers.
  • Surgery goggles should be worn if possible. The specifications of eyewear protection depend on the type of laser, delivery device, and procedure. The correct safety goggles need to be worn for the specific laser in use.
  • The surgeon should be aware of hand placement and protection as a surgeon’s hands are usually the closest to treatment lasers and reflective surgical instruments.

Staff and Bystander Safety[5][7]

  • Staff and bystanders may be more vulnerable to hazards due to lack of training or knowledge regarding lasers or the procedure. All authorized personnel allowed into the treatment area should be given the appropriate safety glasses or eye protectors.


In summary, ophthalmic lasers comprise a critical part of the treatment armamentarium for ophthalmic disease but pose some risk to both the laser operator and patient. Specific precautions and training are necessary to ensure appropriate patient and physician safety.

References

  1. Jelínková H. Introduction: the history of lasers in medicine. In: Lasers for Medical Applications: Diagnostics, Therapy and Surgery. Elsevier Ltd; 2013:1-13.
  2. 2.0 2.1 Lin J-T. Progress of medical lasers: Fundamentals and applications. Med Devices Diagnostic Eng. 2016;2(1):36-41.
  3. 3.0 3.1 3.2 Khalkhal E, Rezaei-Tavirani M, Zali MR, Akbari Z. The evaluation of laser application in surgery: A review article. J Lasers Med Sci. 2019;10(Suppl 1):S104-S111.
  4. Austin Health. Lasers in Ophthalmology. Victoria, Australia: Dept of Ophthalmology; 2020.
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Cordero I. Understanding and safely using ophthalmic lasers. Community Eye Heal. 2015;28(92):76-77.
  6. 6.0 6.1 Medical Lasers. FDA.gov. https://www.fda.gov/radiation-emitting-products/surgical-and-therapeutic-products/medical-lasers#lrps. Published September 28, 2020. Accessed December 22, 2020.
  7. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Sliney D. Ophthalmic laser safety. In Fankhauser F, Kwasniewska S, eds. Lasers in Ophthalmology: Basic, Diagnostic and Surgical Aspects. The Hague, The Netherlands: Kugler Publications; 2003:1-10.
  8. 8.0 8.1 Laser, Ophthalmic. Plymouth Meeting, PA: World Health Organization; 2011.
  9. 9.0 9.1 9.2 American National Standards Institute. American National Standard for Safe Use of Lasers in Health Care. Orlando, FL: Laser Institute of America; 2018.
  10. 10.0 10.1 10.2 CFR - Code of Federal Regulations Title 21. Silver Spring, MD: U.S. Food and Drug Administration; 2020.
  11. Marshall J, O’Hagan JB, Tyrer JR. Eye hazards of laser “pointers” in perspective. Br J Ophthalmol. 2016;100(5):583-584.
  12. Marshall J. The safety of laser pointers: Myths and realities. Br J Ophthalmol. 1998;82(11):1335-1338.
  13. 13.0 13.1 13.2 13.3 13.4 Frequently Asked Questions About Lasers. FDA.gov. https://www.fda.gov/radiation-emitting-products/laser-products-and-instruments/frequently-asked-questions-about-lasers. Published March 7, 2018. Accessed December 22, 2020.
  14. Peterson DC, Hamel RN. Corneal reflex. Encyclopedia of Autism Spectrum Disorders. Springer, New York: StatPearls Publishing; 2013:802-802.
  15. Marelli RA, Hillel AD. Effects of general anesthesia on the human blink reflex. Head Neck. 1989;11(2):137-149.
  16. 16.0 16.1 16.2 16.3 16.4 Mainster MA, Stuck BE, Brown J. Assessment of alleged retinal laser injuries. Arch Ophthalmol. 2004;122(8):1210-1217.
  17. 17.0 17.1 17.2 17.3 17.4 17.5 17.6 17.7 17.8 Burling-Phillips L. Managing retinal injuries from lasers. EyeNet Mag. 2009.
  18. 18.0 18.1 18.2 18.3 Barkana Y, Belkin M. Laser eye injuries. Surv Ophthalmol. 2000;44(6):459-478.
  19. 19.0 19.1 19.2 19.3 W. Commiskey P, J. Heisel C, M. Paulus Y. Non-therapeutic laser retinal injury. Int J Ophthalmic Res. 2019;5(1):321-335.
  20. Waage et al. Non-therapeutic laser injury. Physiol Behav. 2017;176(1):139-148.
  21. Huang A, Phillips A, Adar T, Hui A. Ocular injury in cosmetic laser treatments of the face. J Clin Aesthet Dermatol. 2018;11(2):15-18.
  22. Princeton University. Section 2: Laser Hazards. Ehs.princeton.edu. https://ehs.princeton.edu/book/export/html/363. Accessed January 26, 2021.
  23. 23.0 23.1 23.2 Lee W. Ocular Laser Safety. Ophthalmologyweb.com. https://www.ophthalmologyweb.com/Featured-Articles/332958-Ocular-Laser-Safety/. Published January 24, 2017. Accessed December 23, 2020.
  24. Dick HB, Schultz T. A review of laser-assisted versus traditional phacoemulsification cataract surgery. Ophthalmol Ther. 2017;6(1):7-18.
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