Simultaneous Exposure Using 532 and 860 nm lasers for visible lesion thresholds in the rhesus retina

The growth of commercially available, simultaneous multi-wavelength laser systems has increased the likelihood of possible ocular hazard. For example, many systems utilize frequency multiplying methods to produce combinations of visible, near-infrared, and ultraviolet wavelengths. Unfortunately, very little data exists to substantiate the current methods for estimating hazards from simultaneous lasing. To properly assess the retinal hazards from these wavelengths, the retinal effects of 10-s laser irradiation from 532 and 860 nm were determined in non-human primates for four different relative dosage combinations of these wavelengths. This pair of wavelengths represents the typical problem of a visible-wavelength laser combined with an in-band, infrared wavelength that is not as well focused at the retina-a situation difficult to address. To add confidence to the experimental results obtained, a theoretical thermodynamic model was developed to predict the minimal damage threshold for simultaneous wavelengths at 1 h post exposure. The new model calculations and the data obtained are compared with results from one currently accepted method of predicting relative exposure limits from multi-wavelength systems. In addition, the current ANSI-Z136-2000 standard was used to compute the combined MPEs for comparison with measured visible lesion thresholds. A total of 12 eyes were exposed using four different ratios of power levels (532/860 power rations) to determine the contribution to the damage levels from each wavelength. The experimental data were analyzed using probit analysis at both 1-h and 24-h post exposure to determine the minimum-visible-lesion (MVL) thresholds at ED50 values, and these thresholds at 24 h varied from 5.6 mW to 17 mW total intraocular power.