For wavelengths posing a retinal hazard, current laser safety standards specify an unaided eye measurement condition using a 7 mm aperture that is a proxy for a dark adapted human pupil.
In bright ambient conditions the human pupil is generally much smaller. In a perfect lens for an aperture filling beam the diffraction limited spot size of a collimated beam is the fourth power of the pupil size. So it may appear that the standards are overly conservative in outdoor daytime conditions.
However the eye is not a perfect lens. It is generally understood that aberrations increase with pupil size, limiting the optical quality of a dilated pupil, and thus limiting the growth in peak irradiance after focussing as the pupil dilates.
In this work, we leverage existing data sets of aberrations of several hundred eyes and, using a computer eye model, we estimate the peak irradiances achieved at different pupil sizes. We find for the typical eye in these data sets, the hazard posed by a 7 mm beam of fixed radiance, as estimated by the modeled peak retinal irradiance, is significantly reduced by a 3 mm pupil, but does not increase significantly beyond around 5 mm and may indeed be lower for a fully dilated pupil.