Fully alert (4-4)
(Other definitions for open-eyed that I've seen before include "Forming an encrusted mass" , "Astonished - watchful" , "Astonished; fully aware" , "Surprised - aware" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fully alert</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Another definition for wide-awake that I've seen is " Fully alert".)