▁the ▁ability ▁to ▁act ▁as ▁both ▁the ▁exc itable ▁phot op ig ment ▁and ▁as ▁a ▁photo is omer ase . ▁Instead ▁of ▁requiring ▁additional ▁cells ▁to ▁revert ▁between ▁the ▁two ▁is o forms , ▁from ▁all - trans - ret inal ▁back ▁into ▁ 1 1 - cis - ret inal ▁before ▁it ▁can ▁under go ▁another ▁phot otr ans du ction , ▁like ▁the ▁phot ore ceptor ▁con es , ▁which ▁rely ▁on ▁Müller ▁cells ▁and ▁ret inal ▁p ig ment ▁ep ith el ium ▁cells ▁for ▁this ▁conversion , ▁mel an ops in ▁is ▁able ▁to ▁is omer ize ▁all - trans - ret inal ▁into ▁ 1 1 - cis - ret inal ▁when ▁stim ulated ▁with ▁light ▁without ▁help ▁from ▁additional ▁cells . ▁The ▁two ▁is o forms ▁of ▁mel an ops in ▁differ ▁in ▁their ▁spectral ▁sens itivity , ▁for ▁the ▁ 1 1 - cis - ret inal ▁is o form ▁is ▁more ▁respons ive ▁to ▁shorter ▁w avel ength s ▁of ▁light , ▁while ▁the ▁all - trans ▁is o form ▁is ▁more ▁respons ive ▁to ▁longer ▁w avel ength s ▁of ▁light . ▁ ▁Syn apt ic ▁inputs ▁and ▁outputs ▁ ▁Input s ▁ ▁ip R GC s ▁are ▁both ▁pre - ▁and ▁posts yn apt ic ▁to ▁dop am iner g ic ▁am ac r ine ▁cells ▁( DA ▁cells ) ▁via ▁reci pro cal ▁syn aps es , ▁with ▁ip R GC s ▁sending ▁exc itat ory ▁signals ▁to ▁the ▁DA ▁cells