A computer model was developed for calculating the intraocular energy producing a thermally induced retinal threshold lesion upon exposure to optical radiation. The model parameters were adjusted to best fit the threshold levels reported in the literature in-vivo, with nonhuman primates at wavelengths between 413 and 1338 nm, exposure durations between 100 μs and 50 min, and various retinal spot sizes and exposures to paramacular or macular sites. Comparison of the calculated thresholds with all consistent experimental results published over the past 50 years shows good agreement with a standard deviation of 31%. This validates the model to be used for quantitative predictions of retinal injury thresholds as well as for risk analysis of laser products and supports the development of exposure limits. The spread of data suggests that accuracy cannot be improved much further due to experimental uncertainties and intersubject variability.

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The exposure and emission limits of ICNIRP, IEC 60825-1 and ANSI Z136.1 to protect the cornea are based on a limited number of in-vivo studies. To broaden the database, a computer model was developed to predict injury thresholds in the wavelength range from 1050 nm to 10.6 µm and was validated by comparison with all applicable experimental threshold data (ED50) with exposure duration between 1.7 ns and 100 s. The model predictions compare favorably with the in-vivo data with an average ratio of computer prediction to ED50 of 0.94 (standard deviation ± 30%) and a maximum deviation of less than 2. This computer model can be used to improve exposure limits or for a quantitative risk analysis of a given exposure of the cornea.

We present a computer model for predicting the median dose (ED 50) that produces an ophthamoscopically detectable lesion in the retina. It consists of an optical model (beam propagation through the eye), a reflectance model (absorption distribution within the retinal tissues), a thermal model (solving the heat equation) and a damage model (based on the Arrhenius equation). The model was validated with 253 experimental ED 50 s that cover the entire thermal regime in both macular and paramacular regions encompassing wavelengths between 413 nm and 1338 nm, pulse durations between 100 μs and 3000 s and retinal spot sizes ranging from minimum to 2 mm. These ED 50 s are matched with a mean ratio of 0.93 and a standard deviation of 31 %. The largest ratio between model prediction and experimental data was 1.7. The applicability for using the model results for risk analysis for human exposure is discussed.

The current laser safety standards do not address specifically how to account for repetitively pulsed lasers with irregular pulse trains. Variations in peak power, pulse duration, and duty cycle within a pulse train pose a number of problems when it comes to product classification or to assess the hazard of a given exposure. This study proposes to analyze irregular pulse trains by generalizing the determination of the number of pulses N used in the IEC 60825-1 or n in the ANSI Z136.1 standard. The proposed method for the determination of N applies to emission durations longer than 5 μs and was validated by generating a large number of theoretical pulse patterns and by comparing the retinal injury threshold, determined with a computer model, with the applicable emission limit. For 18 000 different pulse patterns, the ratio of the injury threshold to the emission limit was never less than 2, which is commonly considered as a sufficient safety margin. The smallest safety margin found for regular pulse patterns also equals 2. This study validates an analysis method for irregular pulse trains that can be included in the standards by simple generalization of the determination of the parameter N.