[8][9][10] The name rhodopsin derives from Ancient Greek ῥόδον (rhódon) for "rose", due to its pinkish color, and ὄψις (ópsis) for "sight".

[12][13] When George Wald discovered that rhodopsin is a holoprotein, consisting of retinal and an apoprotein, he called it opsin, which today would be described more narrowly as apo-rhodopsin.

[14] Today, the term opsin refers more broadly to the class of G-protein-coupled receptors that bind retinal and as a result become a light-sensitive photoreceptor, including all closely related proteins.

[7][19] Rhodopsin most strongly absorbs green-blue light (~500 nm)[20][21] and appears therefore reddish-purple, hence the archaic term "visual purple".

[23][24] GPCRs are chemoreceptors that embed in the lipid bilayer of the cell membranes and have seven transmembrane domains forming a binding pocket for a ligand.

[25][26] The ligand for rhodopsin is the vitamin A-based chromophore 11-cis-retinal,[27][28][29][30][31] which lies horizontally to the cell membrane[32] and is covalently bound to a lysine residue (lys296)[33] in the seventh transmembrane domain[34][32] through a Schiff-base.

However, the high density also is a disadvantage when it comes to G protein signaling because the needed diffusion becomes more difficult in a crowded membrane that is packed with rhodopsin.

[58] In subsequent intermediates lumirhodopsin and metarhodopsin I, the Schiff's base linkage to all-trans retinal remains protonated, and the protein retains its reddish color.

[59] The product of light activation, Metarhodopsin II, initiates the visual phototransduction second messenger pathway by stimulating the G-protein transducin (Gt), resulting in the liberation of its α subunit.

In general, the defect rhodopsin aggregates with ubiquitin in inclusion bodies, disrupts the intermediate filament network, and impairs the ability of the cell to degrade non-functioning proteins, which leads to photoreceptor apoptosis.

[63] Several other pathological states relating to rhodopsin have been discovered including poor post-Golgi trafficking, dysregulative activation, rod outer segment instability and arrestin binding.