▁the ▁whole , ▁or ▁part , ▁of ▁a ▁cor nea ▁is ▁replaced . ▁The ▁don or ▁t issue ▁can ▁now ▁be ▁held ▁for ▁days ▁to ▁even ▁weeks ▁of ▁the ▁don or ’ s ▁death ▁and ▁is ▁normally ▁a ▁small , ▁rounded ▁shape . ▁The ▁main ▁use ▁of ▁the ▁cor ne al ▁button ▁is ▁during ▁procedures ▁where ▁the ▁entire ty ▁of ▁the ▁cor nea ▁needs ▁to ▁be ▁replaced , ▁also ▁known ▁as ▁pen etr ating ▁ker at op last y . ▁ ▁History ▁ ▁Greek ▁phys ician ▁Gal en ▁is ▁said ▁to ▁have ▁first ▁consider ▁the ▁possibility ▁of ▁cor ne al ▁trans plant ation ▁however , ▁there ▁is ▁no ▁evidence ▁that ▁he ▁actually ▁attempted ▁the ▁procedure . ▁It ▁was ▁only ▁until ▁the ▁ 1 8 th ▁century ▁that ▁early ▁surg ical ▁propos als ▁for ▁ker at op last y ▁would ▁arise ▁and ▁the ▁ 1 9 th ▁century ▁for ▁experiment ation ▁in ▁the ▁field ▁to ▁begin . ▁ ▁In ▁ 1 8 1 3 , ▁Karl ▁Him ley ▁suggested ▁that ▁op aque ▁animal ▁cor ne as ▁can ▁be ▁replaced ▁by ▁trans plant ing ▁cor ne as ▁from ▁other ▁animals ; ▁with ▁his ▁student ▁Franz ▁Re isen ger ▁comm encing ▁experiment ation ▁in ▁ 1 8 1 8 . ▁ ▁In ▁ 1 8 4 4 , ▁Edward ▁K iss am ▁under to ok ▁the ▁first ▁ever ▁recorded ▁attempt ▁of ▁a ▁x en og raft ▁on ▁a ▁human ; ▁the ▁don or ▁was ▁a ▁p ig ▁and ▁was ▁ultimately ▁un success ful . ▁Henry ▁Power