Illustration that represents the different structures of the eye, divided in the
anterior and posterior segments. The different barriers that drugs need to
overcome after topical installation are indicated with a red star, and a
detailed representation is also provided. The ocular targets to treat a specific
disease are indicated with a green star, if they are in the anterior segment, or
with a yellow star, if they are located in the posterior segment. Reproduced
from Ref. [4] with
permission. Copyright 2015, Elsevier.