( ( When ( ( light ( -LRB- ( ( from ( any source ) ) -RRB- ) ) ) ( ( enters ( the eye ) ) ( through ( the pupil ) ) ) ) ) ( , ( ( ( a part ) ( of ( that light ) ) ) ( ( will ( be ( ( ( reflected ( back out ) ) ( of ( the eye ) ) ) ( by ( the tumors ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NN light)) (PRN (-LRB- -LRB-) (PP (IN from) (NP (DT any) (NN source))) (-RRB- -RRB-))) (VP (VBZ enters) (NP (DT the) (NN eye)) (PP (IN through) (NP (DT the) (NN pupil)))))) (, ,) (NP (NP (DT a) (NN part)) (PP (IN of) (NP (DT that) (NN light)))) (VP (MD will) (VP (VB be) (VP (VBN reflected) (ADVP (RB back) (RB out)) (PP (IN of) (NP (DT the) (NN eye))) (PP (IN by) (NP (DT the) (NNS tumors)))))) (. .)))
When light (from any source) enters the eye through the pupil, a part of that light will be reflected back out of the eye by the tumors.
(ROOT (S (NP (NP (DT The) (NN pupil)) (PP (IN of) (NP (DT the) (NN eye)))) (VP (VBZ allows) (ADJP (JJ light) (S (VP (TO to) (VP (VB enter)))))) (. .)))
The pupil of the eye allows light to enter.