Melanopsin is an unusual vertebrate photopigment that, in mammals, is expressed in a small subset of intrinsically photosensitive retinal ganglion cells (ipRGCs), whose signaling has been implicated in non-image forming vision, regulating such functions as circadian rhythms, pupillary light response, and sleep. The biochemical cascade underlying the light response in ipRGCs has not yet been fully elucidated, but is hypothesized to involve Gq pathway. We present both a deterministic and a stochastic model of the hypothesized melanopsin phototranduction cascade. Both models qualitatively reproduce experimental results under several different conditions. The models allow us to probe various mechanisms in the phototransduction cascade in a way that is currently experimentally not feasible.