Retinal Photoreception

The current textbook perception on the way light is transduced in the retina is based on the association and dissociation of the photoactive pigment retinal with/from rhodopsin, subject to a conformation change of the membrane-bound protein. We believe that this mechanistic perspective on vision is not kinetically or mechanistically sound. Further, we believe that the architecture of the eye does not permit rod and cone cells to be the primary photoreceptors within the eye. The figure below depicts the broad architecture/structure of eye/retina and shows the directions of incident light and action potential purportedly generated.

However, if the rod and cone cells (which are present in the distal part of retina) were to be the original photo-transducing cells deciphering the image falling on the retina, then the eye's evolutionary structure would have been different, as shown in the bottom panel of the figure above. Therefore, we present a new way of looking at the overall process, as shown below.

As can be seen, oxygen is an obligatory component in the visual cycle and rhodopsin-retinal serves as a one-electron transducer in the overall process, supplying the electron deficiency within the photoreceptive cells within the proximal layers. The theory is supported by the known photochemistry of retinal and the structural comparison of the rods/cones with chloroplasts and cyanobacteria, as shown below.