Melanopsin is a visual opsin present in Intrinsically photosensitive retinal ganglion cell (ipRGC) also with a retinal chromaphore. However, unlike the rod and cone pigments, melanopsin has the ability to act as both the excitable photopigment and as a photoisomerase. Melanopsin is therefore able to isomerize all-trans-retinal into 11-cis-retinal itself when stimulated with another photon. An ipRGC therefore does not rely on Müller cells and/or retinal pigment epithelium cells for this conversion.