The light output of ten operating microscope illuminators used for eye surgery was measured. The spectral output characteristics of each source were compared to optical radiation safety standards. Exposure of sensitive ocular structures of the patient is discussed. The light sources tested were found to be safe for momentary viewing, and almost all devices sufficiently filtered IR wavelengths to preclude acute thermal bioeffects. The permissible occupational exposure duration was found to range from 2 min to 1 h. Interpretations of these findings to the clinical setting are provided. Light exposure of the retina should be minimized by using the lowest light setting commensurate with the surgical task and making maximal use of off-axis illumination to minimize central retinal (macular) exposure. It is also recommended to use eyecups to shield the retina during final suturing.
David H. Sliney and Brett C. Armstrong, "Radiometric evaluation of surgical microscope lights for hazards analyses," Appl. Opt. 25, 1882-1889 (1986)