Dr. Mohammad Akkawe
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The lacrimal glands are paired almondshaped glands, one for each eye, that secrete
the aqueous layer of the tear film.
They are situated in the upper, outer portion
of each orbit, in the lacrimal fossa of the orbit
formed by the frontal bone.
Anatomists divide the gland into two sections.
 The smaller palpebral portion, lies close to the eye,
along the inner surface of the eyelid; if the upper
eyelid is everted, the palpebral portion can be seen.
 The orbital portion contains fine interlobular ducts
that unite to form 3 - 5 main excretory ducts, joining
5 - 7 ducts in the palpebral portion before the
secreted fluid may enter on the surface of the eye.
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The lacrimal gland is
tubuloacinar gland derived
from surface ectoderm
with ducts lined by a low
columnar or cuboidal
epithelium (often
bilayered).
The secretory cells in the
acini have a predominance
of dense granules,
suggesting that most are
of a serous nature
However, some cells are
mucus producing
The lobules of the
orbital portion of the
lacrimal gland are near
the orbital septum but
lie under the levator
muscle.
 The fornix of the upper
eyelid lies immediately
adjacent to the
accessory lacrimal
gland of Krause
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The glands of Krause are
accessory lacrimal glands
having the same structure as
the main gland.
They are placed deeply in
the subconjunctival
connective tissue (mainly) of
the upper fornix between
the tarsus and the inferior
lacrimal gland, of which they
are offshoots.
There are some 42 in the
upper and 6 to 8 in the lower
fornix.
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Glands of Wolfring are
also accessory lacrimal
glands, but larger than
the glands of Krause.
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There are 2 to 5 in the
upper lid situated
actually in the upper
border of the tarsus
about its middle
between the extremities
of the tarsal glands or
just above the tarsus.
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The postganglionic
secretomotor fibres
(which arise from the
pterygopalatine
ganglion) “hitch-hike”
on the
zygomaticotemporal
and lacrimal nerves
to the gland
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The accessory lacrimal tissue found at various
sites in the conjunctiva is histologically
identical to the main lacrimal gland, as are
the secretions it produces
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Tear secretion can be classified as basal
secretion and reflex secretion
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the concept of “basal” tear production is a
redundant one, as even minimal tear
production in the undisturbed eye is thought
to be secondary to light or temperature
stimulation or both
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Reflex tearing is mediated via
parasympathetic nerves that stimulate the
myoepithelial cells lining lacrimal acini,
causing them to contract
These fibers originate in the superior
salivatory nucleus and lesions in this region
will reduce reflex tearing
Sympathetic nerves may influence tear
production by altering the blood flow to
the lacrimal glands
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The underlying mechanism of psychogenic
tearing is not clearly understood, but it is
always bilateral
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The original model of the precorneal tear film
described a trilayered film composed of:
anterior lipid layer,
 middle aqueous layer
 an inner hydrophilic mucin layer produced
by the goblet cells
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lipid
Aqueous
Mucoid
Location
Anterior
Middle
@ the corneal
epithelium
Thickness
0.1 µm
10 µm
30 µm
Secreted by
Meibomian glands,
glands of Zeis
Lacremal glands,
accessory lacremal
gland
Conjunctiva
Function
Reduces
evaporation.
Prevents
overflow from lid
margin
Contains
nutrients.
Uptakes O2 from
cornea
Allows the tear
film to spread
evenly on a
hydrophopic
corneal surface
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Until recently it was
thought that the mucin
layer is <o.o5µm,
however it was
discovered by modern
imaging techniques that
the actual thickness is
30µm and that the tear
film is a mucus
dominated gel hydrated
by aqueous fluid
Mucin secreting cells are found throughout
the conjunctiva with a maximal concentration
inferonasally
 The stability of the tear film is dependent on:
 the epithelial glycocalyx
 the antievaporative effects of the lipid layer
 the viscous properities of the tears imparted
by the mucin layer
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The tear film break-up time is a crude
measure of tear film stability, and is of the
order of 10-30 seconds in normal eyes
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The maximum volume of the conjunctival sac
is 20 µm but the normal tear volume is
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approximately 6-7 µm because of the
effect of blinking
This explains why only 20% of an average
drop of medication (approximately 50 µm) is
retained in the conjunctival sac, the rest
being lost to overflow
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A tear turnover rate of 18% per minute
compounds poor retention of medication,
which means that after 5 min only 40% of
the medication is present in the
conjunctival sac
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A normal schrimer’s
test would produce 1525 mm of “wetting”
over a period of 5 mins
The primary secretion from the acinar region of
the lacrimal gland is essentially an ultrafiltrate
of plasma; it is later modified by ductal
secretion of potassium chloride
 This explains elevated potassium (15-30
mmol/l) concentrations, with respect to plasma
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Passive diffusion of electrolytes through the
intercellular spaces of conjunctival or corneal
surface epithelial cells is prevented by tight
junctions
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The osmolarity of the aqueous layer is
approximately that of normal saline and the
PH is 7.4
The precorneal tear film and the limbal
vessels supply the corneal epithelium with
glucose; the glucose concentration in the
aqueous layer is therefore lower than that
of plasma
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The protein components of unstimulated
tears is variable but is usually 7-10 mg/ml
this falls to 3.9mg/ml with high flow rates
The major protein constituents of the
precorneal tear film comprise those produced
by the acinar cells and those derived from
other sources
Production of the acinar derived proteins
lysosyme and lactoferrin rises with increasing
stimulation, and therefore their concentration in
the tear film remains relatively constant
 Lysosyme and lactoferrin are antibacterial
agents; the former breaks down bacterial cell
walls and the latter inhibits the growth of irondependent bacteria and also scavenges free
radicals
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The concentrations of both lactoferrin and
lysosyme decrease with age
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The production of secretory IgA decreases with
increased tear production
Conversely, the levels of secretory IgA rises
markedly at night, as aqueous tear production
by the acinar cells declines
IgG concentrations are very low (0.004g/l) in
the normal tear film compared with those of
secretory IgA levels (1.9 g/l),although IgG levels
are elevated in inflamatory conditions as a result
of leakage from conjunctival vessels
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Tear lipocalin ( formerly known as tear
specific prealbumin) accounts for 20% of tear
film production
It has significant homology with members of
the lipocalin family of proteins, which bind
small hydrophobic molecules
Tear lipocalin was thought to have a
protective effect on the epithelium and has
been shown to inhibit cysteine proteinase
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The tear film lipids are derived from the
meibomian glands, these holocrine glands
excrete a clear oil on to the lid margins in
response to each blink
Most tear film lipids is in the form wax esters
32% and sterol esters 27%
free fatty acids accounting for only 2% of
tear film lipids
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Other lipid components of the tear film
include diesters, triacyl triglycerides and
polar lipids
The profile of free fatty acids and the
proportion of lipid classes varies considerably
between individuals, and may be a factor that
predisposes to the development of chronic
plepharitis
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The composition of lipid after realease is
altered by the action of lipolytic lid margin
bacteria and is invariably different from that
of the lipid originally produced by the
meiobian glands