Potential hazards from specific ophthalmic devices

Abstract

The retinal light exposure a patient might receive from ophthalmoscopes, slit lamps, surgical microscopes, and overhead surgical lamps is documented. Monkey exposures to microscopes and slit lamps were performed to substantiate the findings. A “typical” indirect ophthalmoscope is seen to be “unsafe” after 23 sec of exposure in a patient with dilated pupils and clear media, if compared with laser safety standards. Slit lamp biomicroscopy of the macula produces 2–3 times greater retinal exposure than the indirect ophthalmoscope. Operating microscope internal light sources produce a surprising retinal exposure of up to 10 times greater than the indirect ophthalmoscope over an area of several disc diameters, causing severe choroioretinal lesions in monkeys after 1 hr of continuous exposure. The surgeon's retina receives 44 mW/cm 2 from the corneal specular reflection of the microscope source. Using the laser safety standards, this is “unsafe” after one minute. A prototype surgical illuminator is described which reduces retinal irradiance to 1/900th of that from conventional microscope light sources, while maintaining equivalent illumination of the anterior segment.