The function of PDE6B (phosphodiesterase 6B, ENSG00000133256) is as follows. Catalytic beta subunit of the rod-specific cGMP phosphodiesterase (PDE6) complex, which hydrolyzes 3',5'-cyclic GMP in the phototransduction cascade. The PDE6 holoenzyme consists of two catalytic subunits (PDE6A and PDE6B) and two inhibitory gamma subunits (PDE6G) (PubMed:20940301). Light-activated GNAT1 relieves gamma subunit-mediated inhibition, enabling the catalytic subunits to hydrolyze cGMP and thereby mediate visual signal transduction and amplification (PubMed:8394174). Decreased cytosolic cGMP levels result in closure of cGMP-gated cation channels at the plasma membrane, leading to rod photoreceptor hyperpolarization (Probable). Involved in retinal circadian rhythm photoentrainment via modulation of UVA and orange light-induced phase-shift of the retina clock (By similarity). {ECO:0000250|UniProtKB:P23440, ECO:0000269|PubMed:20940301, ECO:0000269|PubMed:8394174, ECO:0000305}.