Spectral irradiances of and maximal permissible exposures to two indirect ophthalmoscopes

Recent reports in the literature have indicated that exposure to certain high intensity sources used in clinical procedures may be damaging to the retina. To investigate this problem, the spectral irradiance of two indirect ophthalmoscopes [American Optical (AO) and Keeler] was measured. The instruments do show operational differences, the most striking of which was the difference in the total irradiance produced at the maximum voltage setting, the Keeler instrument providing nearly 3.6 times greater irradiance than the AO indirect ophthalmoscope. The sources are evaluated as blue light hazards, and maximal permissible exposures (MPE) are calculated and compared to the MPE established by ANSI Z-136 guidelines.