6 % ▁of ▁her p etic ▁ker at itis ▁cases ▁may ▁evol ve ▁to ▁this ▁disease , ▁with ▁a ▁peak ▁of ▁ 1 2 . 8 % ▁of ▁cases ▁of ▁ker at itis ▁due ▁to ▁var ic ella ▁z oster ▁virus . ▁ ▁The ▁diagn osis , ▁and ▁particularly ▁the ▁treatment ▁of ▁ne uro t roph ic ▁ker at itis ▁are ▁the ▁most ▁complex ▁and ▁challeng ing ▁aspects ▁of ▁this ▁disease , ▁as ▁a ▁satisf actory ▁th era pe ut ic ▁approach ▁is ▁not ▁yet ▁available . ▁ ▁C aus es ▁ ▁The ▁cor nea ▁la cks ▁blood ▁vessels ▁and ▁is ▁among ▁the ▁most ▁dens ely ▁inner v ated ▁structures ▁of ▁the ▁human ▁body . ▁Cor ne al ▁n erves ▁are ▁responsible ▁for ▁maintain ing ▁the ▁an atom ical ▁and ▁functional ▁integrity ▁of ▁the ▁cor nea , ▁con ve ying ▁tact ile , ▁temperature ▁and ▁pain ▁sens ations , ▁playing ▁a ▁role ▁in ▁the ▁bl ink ▁ref lex , ▁in ▁w ound ▁he aling ▁and ▁in ▁the ▁production ▁and ▁secret ion ▁of ▁tears . ▁ ▁Most ▁cor ne al ▁n erve ▁fib res ▁are ▁sens ory ▁in ▁origin ▁and ▁are ▁derived ▁from ▁the ▁o ph th al mic ▁branch ▁of ▁the ▁trig em inal ▁n erve . ▁Cong en ital ▁or ▁acquired ▁oc ular ▁and ▁system ic ▁dise ases ▁can ▁determine ▁a ▁les ion ▁at ▁different ▁levels ▁of ▁the ▁trig em inal ▁n erve , ▁which ▁can ▁lead ▁to ▁a ▁reduction ▁( hy po est hes ia ) ▁or ▁loss ▁( an est