The axons of the retinal ganglion cells in our eyes form the optic nerve. These neuronal cells are divided into two groups: image forming neurons, which are connected to the visual cortex and underlie image formation (~98% of the neurons) and non-image forming neurons, which are connected to the supra chiasmatic nucleus in the hypothalamus (~2% of the neurons). The latter small group calibrate by direct photic input the circadian pacemaker of the master circadian clock (the major biological clock that has many functions, including generation of jetlag) and support non-image forming (NIF) light dependent functions critical for our health. The neurons of the small group are called "intrinsically photosensitive retinal ganglion cells (ipRGC)" because they express the light activated melanopsin (OPN4) photopigment. There are difficulties in advancing understanding of ipRGC phototransduction (the process in which the light is translated into electrical signals understood by the brain). The main obstacle is the scarcity of ipRGCs and the low expression levels of phototransduction proteins in these cells. This difficulty makes it nearly impossible to investigate phototransduction of the ipRGC by employing the same set of biochemical and electrophysiological approaches that proved successful in characterizing rhodopsin signaling processes in image forming rod and cones photoreceptor cells. Therefore, at present the knowledge of phototransduction of ipRGC is still fragmented. A promising way to characterize the OPN4 photopigment arises from the apparent similarity between phototransduction of ipRGC and the fly. It has been well established that several features of ipRGC photosensitivity are characteristic of Drosophilaphotosensitivity. However, a major difference is the extremely slow light-response kinetics of ipRGC, which is in sharp contrast to the fast kinetics of fly phototransduction. The slow kinetics of ipRGC prevents using melanopsin expressing retinal cells as a promising tool for visual restoration of the blind in most cases of human blindness.