( ( ( ( ( ( A ( concave ( or ( minus lens ) ) ) ) ( is ( used ( to ( correct ( ( ( ( myopia ( -LRB- ( nearsightedness -RRB- ) ) ) , ) and ) ( a convex ) ) ) ) ) ) ) , ) or ) ( ( plus lens ) ( is ( used ( to ( correct ( hyperopia ( -LRB- ( farsightedness -RRB- ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (DT A) (NN concave) (CC or) (NN minus) (NN lens)) (VP (VBZ is) (VP (VBN used) (S (VP (TO to) (VP (VB correct) (NP (NP (NP (NN myopia)) (PRN (-LRB- -LRB-) (NP (NNP nearsightedness)) (-RRB- -RRB-))) (, ,) (CC and) (NP (DT a) (NN convex))))))))) (, ,) (CC or) (S (NP (IN plus) (NN lens)) (VP (VBZ is) (VP (VBN used) (S (VP (TO to) (VP (VB correct) (NP (NP (NN hyperopia)) (PRN (-LRB- -LRB-) (NP (NNS farsightedness)) (-RRB- -RRB-))))))))) (. .)))
A concave or minus lens is used to correct myopia (nearsightedness), and a convex, or plus lens is used to correct hyperopia (farsightedness).
(ROOT (S (NP (JJ Concave) (NNS lenses)) (VP (MD can) (VP (VB correct) (NP (NN myopia)))) (. .)))