▁major ▁causes ▁of ▁blind ness ▁world wide ▁such ▁as ▁gla u com a , ▁a ▁disease ▁which ▁affect s ▁gang l ion ▁cells . ▁ ▁In ▁other ▁m amm als , ▁photos ens itive ▁gang lia ▁have ▁proven ▁to ▁have ▁a ▁genu ine ▁role ▁in ▁conscious ▁vision . ▁Test s ▁conducted ▁by ▁Jenn ifer ▁E cker ▁et ▁al . ▁found ▁that ▁r ats ▁lack ing ▁ro ds ▁and ▁con es ▁were ▁able ▁to ▁learn ▁to ▁sw im ▁toward ▁sequences ▁of ▁vertical ▁bars ▁rather ▁than ▁an ▁equally ▁lum ines cent ▁gray ▁screen . ▁ ▁V io let - to - blue ▁light ▁▁ ▁Most ▁work ▁suggests ▁that ▁the ▁peak ▁spectral ▁sens itivity ▁of ▁the ▁re ceptor ▁is ▁between ▁ 4 6 0 ▁and ▁ 4 8 4   nm . ▁Lock ley ▁et ▁al . ▁in ▁ 2 0 0 3 ▁showed ▁that ▁ 4 6 0   nm ▁( blue ) ▁w avel ength s ▁of ▁light ▁suppress ▁mel aton in ▁twice ▁as ▁much ▁as ▁ 5 5 5   nm ▁( green ) ▁light , ▁the ▁peak ▁sens itivity ▁of ▁the ▁phot op ic ▁visual ▁system . ▁In ▁work ▁by ▁Za idi , ▁Lock ley ▁and ▁co - auth ors ▁using ▁a ▁rod less , ▁con eless ▁human , ▁it ▁was ▁found ▁that ▁a ▁very ▁inten se ▁ 4 8 1   nm ▁stim ulus ▁led ▁to ▁some ▁conscious ▁light ▁per ception , ▁meaning ▁that ▁some ▁rud iment ary ▁vision ▁was ▁realized . ▁ ▁Disc overy ▁ ▁In ▁ 1 9 2