In the visible wavelength range, the current laser safety MPEs to protect the retina issued by ANSI Z136.1, IEC 60825-1 and ICNIRP are constant, i.e. do not feature a wavelength dependence. It has been shown before by David Jack Lund in the pulsed regime that a wavelength dependence exists and can be theoretically supported by the pre-retinal absorption factors as well as the absorption in the RPE as function of wavelength. However, we show in this paper that the transmission/absorption-based wavelength dependence only applies to short pulses, where heat flow does not play a role. Computer modelling shows that the longer the exposure duration becomes, the flatter the wavelength dependence becomes, so that for the cw case the constant MPE in the visible wavelength range is an appropriate trend that is not unduly over-restrictive. For the pulsed regime, a constant wavelength dependence might be over-restrictive in the red wavelength range, but has the advantage of being simple.
Also, raising MPEs has to be done with care in order to sustain a sufficient safety margin, while lowering the MPEs should only be done when the current MPEs were found to be associated to a safety margin that is too small. The data is also relevant for an ongoing revision of the international safety standard for ophthalmic instruments, ISO 15004-2 and the USA standard for ophthalmic instruments, ANSI Z80.36.