( ( ( focus ( on ( the pupil ) ) ) ( when ( they ( open ( their eyes ) ) ) ) ) . )
(ROOT (S (VP (VB focus) (PP (IN on) (NP (DT the) (NN pupil))) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (VP (VBP open) (NP (PRP$ their) (NNS eyes)))))) (. .)))
focus on the pupil when they open their eyes.
(ROOT (S (NP (NP (DT The) (NN opening)) (PP (IN in) (NP (NP (DT the) (NN front)) (PP (IN of) (NP (DT the) (NN eye)))))) (VP (VBZ is) (VP (VBN called) (NP (NN pupil)))) (. .)))