Radiation of the fiberoptic illuminator of an operating microscope.

Relative radiation spectrum of a fiberoptic illuminator of an operating microscope (Zeiss Opmi 6) was measured with a spectrophotometer within the range of 350 to 1100 nm. Total irradiance at the corneal level was measured with a radiometer within the range of 250 to 4000 nm. Illumination was measured with a standard illuminometer. Two selective filters were used to optimally reduce the total radiation. A Schott filter GG 420 was used to cut off ultraviolet radiation and a Schott thermal filter KG 1 to reduce intrared radiation. Measured without filters the energy of radiation of wavelengths shorter than 400 nm was only 0.05% of the total energy of radiation, 78.5% was within the range of 400 to 780 nm, and 21.4% was produced by radiation of wavelengths longer than 780 nm. Corresponding values measured with selective filters were 0.003, 95.4 and 4.6. Irradiance at the corneal level was 7.7 mW/cm2 without filters and 3.8 mW/cm2 with selective filters, and the corresponding illumination levels were 21,300 and 16,500 lux. Using selective filters the total irradiance was effectively reduced causing only a minor reduction of the illumination level and a small just noticeable alteration of the colour of the operating field.