Desperately need a key to perception without enhancement (5,3)
I believe the answer is:
naked eye
'perception without enhancement' is the definition.
(what the eye sees on its own)
'desperately need a key' is the wordplay.
'desperately' is an anagram indicator.
'need'+'a'+'key'='needakey'
'needakey' anagrammed gives 'NAKED EYE'.
'to' is the link.
(Other definitions for naked eye that I've seen before include "Unaided vision" , "(View) unaided by any optical instrument" , "With which to observe" , "Unassisted sight" , "Unenhanced vision" .)