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Dry
eye
disease
compounds…

more
tear
components
(7).
Tear
film
forms
a
moist
natural
barrier
separating
eye

from
the
external
media.
This
consistent
film
is
formed
mainly
from
a
triplet
of

aqueous,
mucous,
and
lipid
layers
providing
the
necessary
equilibrium
for
the

healthy
maintenance
of
the
ocular
surface
(Figure
1).

The
main
functions
of
this

film
are:
lubrication
of
the
ocular
surface,
transfer
of
nutritional
elements
to
the

cornea,
elimination
of
foreign
matter
and
cellular
debris
generated
on
the
ocular

surface
by
the
tear
flow
and
the
blink
process,
and
acting
as
the
first
line
of
defense

against
ocular
surface
infections

(8).
In
some
cases,
the
imbalance

of
the
tear
film
composite
layers

leads
to
reduced
tear
secretion,

exposure
of
the
eye
surface,

dryness
and
damage
of
the

surface
cells
(6).
The
imbalance

of
the
composite
layers
could
be

caused
by
Sjögren’s
syndrome

tear
secretion
deficiency
and/or

tear
film
instability
due
to
the
Figure
1.-­-
Tear
film
layers.

use
of
contact
lenses
(6,
9,
10).

Dry
eye
syndrome
types
are
classified
according
to
etiologic
perspectives
and

environmental
influences
as:
aqueous
deficient
dry
eye
(ADDE)
and
evaporative-­-

tear
dry
eye
(EDE)
(6,
11).
ADDE
is
divided
to:
related
to
Sjögren’s
syndrome

(primary
and
secondary)
and
non-­-related
to
Sjögren’s
syndrome
conditions

(lacrimal
disease,
lacrimal
obstruction
and
malfunctioning
blinking
reflex)
(6).
EDE

conditions
are:
oil
deficient,
lid
related
and
caused
by
an
ocular
surface
alteration

(6).
Signs
and
symptoms
of
these
complications
can
vary
from
patient
to
patient,

sometimes
with
little
or
no
correlation
between
them,
even
though
they
are

generally
related
to
the
tear
film
composition.
The
signs
and
symptoms
could

include
keratitis,
conjunctival
and
corneal
staining,
redness,
blurry
vision,

decreased
tear
film
break-­-up
time,
decreased
tear
production,
volume,
and
flow,

increased
conjunctival
redness,
excess
debris
in
the
tear
film,
ocular
dryness,

ocular
grittiness,
ocular
burning,
foreign
body
sensation
in
the
eye,
excess
tearing,

photophobia,
ocular
stinging,
refractive
impairment,
ocular
sensitivity,
and
ocular

irritation
(12,
13).

The
clinical
diagnosis
of
dry
eye
is
challenging
since
dry
eye
is
a
pathology

characterized
by
an
extensive
variety
of
signs
and
symptoms,
mentioned
above,

related
to
ocular
dryness
and
the
ambiguity
in
the
etiology
and
pathophysiology
of

153