Fig 6. Excitation and metabolic cycle of rhodopsin depending on the use of the blue-blocking filter.

(A) In the presence of light of all wavelengths, rhodopsin absorption spectrum falls below the black curve. (B) When a blue-blocking filter is used, the spectrum is only possible in the space below the black curve limited by the red line. (C) All-trans Retinal (atRal) is generated after rhodopsin excitation. This may follow two different pathways depending on the excitation wavelength: after a blue-green-yellow flash (400 to 600 nm) or after a green-yellow flash (500 to 600 nm). Both pathways are represented to the right and left of the rhodopsin molecule, respectively. In high and continuous light exposure, total bleaching of rhodopsin takes place and much toxic atRal is accumulated. Then, atRal is slowly recycled to MII in a process that involves blue light (photoreversal). Blue light is also implied in MIII storage increase. The huge atRal accumulation and its photoactivation by blue light have important implications for photoreceptors, like the genesis of photoreactive metabolites (A2E and lipofuscin). Also, in the presence of molecular oxygen, photo-oxidative reactions are initiated, as well as blocking of its conveyor ABCA4 and subsequent action of retinal dehydrogenase (in rods, RDH8) (red arrow). Conversely, in the absence of blue light all these processes disappear or are strongly attenuated (right side of the drawing). Gray arrows indicate a decreased effect or a blockade.