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Laser safety calculations for optical systems are often based on the assumption of ideal symmetrical retinal images or exposure scenarios. The laser safety standard IEC 60825-1:2014 uses exposure limits from the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines, which refer to symmetrical spots. Further, the standard is premised on retinal damage thresholds of symmetrical exposure scenarios, which are empirically determined in laser damage experiments or simulations. In reality, retinal images of laser systems feature aberration-afflicted, asymmetrical retinal geometries, for example resulting from optical aberrations such as coma and astigmatism. Especially for these asymmetrical retinal exposure scenarios, the laser safety standard ensures that the optical systems are eye-safe by specifying a symmetrization of the retinal image, emission limits and safety factors. In terms of safety and performance of the laser systems, it is particularly important to directly consider asymmetrical retinal images and therefore be able to assess the size of the safety factors. For this consideration, a computer model is recommended, which is an eye and thermal simulation model, handles asymmetrical retinal images and calculates damage thresholds of these exposure scenarios.
A computer model for symmetrical retinal geometries exists, which is validated on experimental data of nonhuman primates (NHP) and uses a finite element method (FEM) simulation to solve the heat transfer equation. Further, it is also used to calculate retinal damage thresholds by inserting the temperature behavior into the Arrhenius equation. The focus of the work presented here is the extension and further development of the computer model and elaborates the difficulties to simulate retinal damage thresholds of asymmetrical exposure scenarios. In particular, the extension of this computer model to asymmetrical retinal images while maintaining validation is addressed. An exemplary case of an asymmetrical retinal image is calculated with the model and the results are presented.
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