LIGHT HAZARDS IN THE OPERATING ROOM Claude L. Cowan, Jr, MD Washington, DC
The use of high-intensity illumination devices is routine for many ophthalmic diagnostic and therapeutic procedures. However, the exposure of patients to high-level photic energy may be damaging even in the absence of visible abnormalities. Devices such as the operating microscope, indirect ophthalmoscope, and endoilluminator are capable of irradiances sufficient to cause retinal damage and should be used with a degree of restraint that reflects a recognition of their potential for phototoxicity. (J NatI Med Assoc. 1992;84:425-429.) Key words * light hazards * operating room0
phototoxicity Diagnostic and therapeutic techniques in ophthalmology have traditionally relied on high-intensity illuminating devices to aid in visualization. Although these procedures generally have been considered safe, some evidence suggests that exposure of the eye to moderate- and even low-intensity light sources may be damaging. 1-4 Light interactions with tissues depend on the relationship that defines the amount of energy delivered per unit time. These effects range from mechanical disruption from high-energy nanosecond or picosecond pulses to photochemical reactions that may take anywhere from hours to days to become clinically apparent. Intermediate between these two are light/tissue interactions associated with a rise in tissue temperature sufficient to cause coagulation. The photo-disruptive From the Division of Ophthalmology, Howard University College of Medicine, Washington, DC. Presented at the Howard University Symposium on Ocular Phototoxicity, March 9-10, 1990, St Thomas, USVI. Requests for reprints should be addressed to Dr Claude L. Cowan, Jr, Associate Professor, Division of Ophthalmology, Howard University Hospital, 2041 Georgia Ave, NW, Washington, DC 20060. JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 84, NO. 5
and coagulative properties of light are used therapeutically. Photochemical injury, however, has no clinical usefulness alone but may be important in the evolution of certain ocular disorders, most notably cataract, pterygium, and macular degeneration. In addition, photochemical injury is also felt to play a role in iatrogenic phototoxicity from nonlaser light sources. The retina is sensitive to photochemical effects, especially from the blue and ultraviolet (UV) end of the spectrum.3-8 This may be due in part to the high absorption by human rhodopsin and cone pigments in the near UV region and may explain the propensity of certain light sources to cause retinal injury. Patients are exposed to a variety of light sources in the operating room. Three of them, the operating microscope, the indirect ophthalmoscope, and the endoilluminator have sufficient light output to pose potential threats to the eye. Hochheimer et al first demonstrated the ability of the operating microscope to cause clinically apparent damage.9 They were able to produce visible retinal lesions in primates after a 1-hour exposure. It was noted that filtering out the blue portion of the spectrum reduced but did not eliminate these lesions. Subsequently, Calkins and Hochheimer developed a model for calculating retinal irradiance produced by several operating microscopes in clinical use. 1 They predicted that in typical clinical usage, retinal exposures could exceed American National Standards Institute (ANSI) safety standards for exposure to laser light sources. In the worse case scenario, Calkins and Hochheimer calculated that visible retinal lesions could be produced in as little as 5 to 8 minutes. Despite the concern raised by these two studies, it was not until 1983 that significant retinal toxicity from the operating microscope was demonstrated in humans. Berler and Peyser reported on a series of 133 patients randomly assigned to two operating rooms.11 One OR had a high-intensity tungsten filament microscope with considerable output in the blue range while the other 425
LIGHT HAZARDS
Ii_S
The use of high-intensity illumination devices is routine for many ophthalmic diagnostic and therapeutic procedures. However, the exposure of patients to high-level photic energy may be damaging even in the absence of visible abnormalities. Devices such as the operating microscope, indirect ophthalmoscope, and endoilluminator are capable of irradiances sufficient to cause retinal damage and should be used with a degree of restraint that reflects a recognition of their potential for phototoxicity. (J NatI Med Assoc. 1992;84:425-429.) Key words * light hazards * operating room0
phototoxicity Diagnostic and therapeutic techniques in ophthalmology have traditionally relied on high-intensity illuminating devices to aid in visualization. Although these procedures generally have been considered safe, some evidence suggests that exposure of the eye to moderate- and even low-intensity light sources may be damaging. 1-4 Light interactions with tissues depend on the relationship that defines the amount of energy delivered per unit time. These effects range from mechanical disruption from high-energy nanosecond or picosecond pulses to photochemical reactions that may take anywhere from hours to days to become clinically apparent. Intermediate between these two are light/tissue interactions associated with a rise in tissue temperature sufficient to cause coagulation. The photo-disruptive From the Division of Ophthalmology, Howard University College of Medicine, Washington, DC. Presented at the Howard University Symposium on Ocular Phototoxicity, March 9-10, 1990, St Thomas, USVI. Requests for reprints should be addressed to Dr Claude L. Cowan, Jr, Associate Professor, Division of Ophthalmology, Howard University Hospital, 2041 Georgia Ave, NW, Washington, DC 20060. JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 84, NO. 5
and coagulative properties of light are used therapeutically. Photochemical injury, however, has no clinical usefulness alone but may be important in the evolution of certain ocular disorders, most notably cataract, pterygium, and macular degeneration. In addition, photochemical injury is also felt to play a role in iatrogenic phototoxicity from nonlaser light sources. The retina is sensitive to photochemical effects, especially from the blue and ultraviolet (UV) end of the spectrum.3-8 This may be due in part to the high absorption by human rhodopsin and cone pigments in the near UV region and may explain the propensity of certain light sources to cause retinal injury. Patients are exposed to a variety of light sources in the operating room. Three of them, the operating microscope, the indirect ophthalmoscope, and the endoilluminator have sufficient light output to pose potential threats to the eye. Hochheimer et al first demonstrated the ability of the operating microscope to cause clinically apparent damage.9 They were able to produce visible retinal lesions in primates after a 1-hour exposure. It was noted that filtering out the blue portion of the spectrum reduced but did not eliminate these lesions. Subsequently, Calkins and Hochheimer developed a model for calculating retinal irradiance produced by several operating microscopes in clinical use. 1 They predicted that in typical clinical usage, retinal exposures could exceed American National Standards Institute (ANSI) safety standards for exposure to laser light sources. In the worse case scenario, Calkins and Hochheimer calculated that visible retinal lesions could be produced in as little as 5 to 8 minutes. Despite the concern raised by these two studies, it was not until 1983 that significant retinal toxicity from the operating microscope was demonstrated in humans. Berler and Peyser reported on a series of 133 patients randomly assigned to two operating rooms.11 One OR had a high-intensity tungsten filament microscope with considerable output in the blue range while the other 425
LIGHT HAZARDS
Ii_S
