Aversion responses including the blink reflex: Psychophysical behaviour and active protection reactions as an additional safety concept for the application of low power lasers in the visible spectrum

Abstract

A version responses, including the blink reflex, were regarded as a sufficient physiological measure in order to protect against laser radiation from laser products of class 2 according to IEC 60825-1 since many years.In a research project, in which originally the dependence of the blink reflex on several factors like stress, tiredness, alcohol and even drugs should have been investigated, we have found in a total of 2,250 volunteers that not more than 18.4 % showed a blink reflex. In a subgroup of 796 volunteers we found that aversion responses, excluding the blink reflex, are an even less frequent event, since only 4.6 % averted after being irradiated by a laser beam belonging to class 2 according to IEC 60825-1 or by using a single chip LED or an LED array consisting of 80 high-brightness pc-LEDs.Since the respective investigations have been made at different wavelengths we were able to search for a relationship between the brightness of the radiation and the frequency of the blink reflex. Based on the known psychophysical laws it can be stated that the blink reflex depends on photometric quantities, but has a much weaker dependence on the applied wavelength compared to the standard photometric spectral visibility function.The results obtained in the various test situations have shown that neither the blink reflex nor conventional aversion responses exist with a sufficient frequency in order to justify the safety philosophy used up to now together with the applied time base of 0.25 s for visible laser radiation.The findings do not state that class 2 or 2M lasers are no longer safe, but the safety factor is reduced due to the lack of a confident inherent physiological protection reaction.Taking a closer look onto the complex behavior of vision and physiology and considering saccades and fixations together with different levels of neuroretinal and cortical processing a new concept of active protection reactions will be recommended in order to guarantee a safe use of low power lasers belonging to class 2 or 2M as a consequence of the current knowledge of the frequent absence of aversion responses, including the blink reflex.In addition the training of active protection reactions might be a valuable contribution in order to prevent against any potentially hazardous radiation from mislabeled class 2 laser products and true class 3R lasers in the visible part of the spectrum.A version responses, including the blink reflex, were regarded as a sufficient physiological measure in order to protect against laser radiation from laser products of class 2 according to IEC 60825-1 since many years.In a research project, in which originally the dependence of the blink reflex on several factors like stress, tiredness, alcohol and even drugs should have been investigated, we have found in a total of 2,250 volunteers that not more than 18.4 % showed a blink reflex. In a subgroup of 796 volunteers we found that aversion responses, excluding the blink reflex, are an even less frequent event, since only 4.6 % averted after being irradiated by a laser beam belonging to class 2 according to IEC 60825-1 or by using a single chip LED or an LED array consisting of 80 high-brightness pc-LEDs.Since the respective investigations have been made at different wavelengths we were able to search for a relationship between the brightness of the radiation and the frequency of the blink reflex. Based on the...