Lacrimal Apparatus Anatomy

The lacrimal apparatus comprises (1) Main lacrimal
gland, (2) Accessory lacrimal glands, and (3) Lacrimal
passages, which include: puncta, canaliculi, lacrimal
sac and nasolacrimal duct (NLD) (Fig. 15.1).
Main lacrimal gland
It consists of an upper orbital and a lower palpebral
part. (1) Orbital part is larger, about the size and
shape of a small almond, and is situated in the fossa
for lacrimal gland at the outer part of the orbital plate
of frontal bone. It has got two surfaces — superior
and inferior. The superior surface is convex and lies
in contact with the bone. The inferior surface is
concave and lies on the levator palpebrae superioris
muscle. (2) Palpebral part is small and consists of
only one or two lobules. It is situated upon the course
of the ducts of orbital part from which it is separated
by LPS muscle. Posteriorly, it is continuous with the
orbital part.
Ducts of lacrimal gland. Some 10-12 ducts pass
downward from the main gland to open in the lateral
part of superior fornix. One or two ducts also open in
the lateral part of inferior fornix.
Accessory lacrimal glands (Fig. 14.4)
1. Glands of Krause. These are microscopic glands
lying beneath the palpebral conjunctiva between
fornix and the edge of tarsus. These are about 42
in the upper fornix and 6-8 in the lower fornix.
2. Glands of Wolfring. These are present near the
upper border of the superior tarsal plate and
along the lower border of inferior tarsus.
Structure, blood supply and nerve supply
Structure. All lacrimal glands are serous acini, similar
in structure to the salivary glands. Microscopically
these consist of glandular tissue (acini and ducts),
connective tissue and puncta.
Blood supply. Main lacrimal gland is supplied by
lacrimal artery which is a branch of ophthalmic artery.
Nerve supply. (1) Sensory supply comes from lacrimal
nerve, a branch of the ophthalmic division of the fifth
nerve. (2) Sympathetic supply comes from the carotid
plexus of the cervical sympathetic chain. (3)
Secretomotor fibres are derived from the superior
salivary nucleus.
Lacrimal passages
1. Lacrimal puncta. These are two small, rounded or
oval openings on upper and lower lids, about 6 and
6.5 mm, respectively, temporal to the inner canthus.
Each punctum is situated upon a slight elevation
called lacrimal papilla which becomes prominent in
old age. Normally the puncta dip into the lacus
lacrimalis (collection of tear fluid in the inner canthus).
2. Lacrimal canaliculi. These join the puncta to the
lacrimal sac. Each canaliculus has two parts: vertical
(1-2 mm) and horizontal (6-8 mm) which lie at right
angle to each other. The horizontal part converges
towards inner canthus to open in the sac. The two
canaliculi may open separately or may join to form
common canaliculus which opens immediately into
the outer wall of lacrimal sac. A fold of mucosa at this
point forms the valve of Rosenmuller which prevents
reflux of tears.
3. Lacrimal sac. It lies in the lacrimal fossa located in
the anterior part of medial orbital wall. The lacrimal
fossa is formed by lacrimal bone and frontal process
of maxilla. It is bounded by anterior and posterior
lacrimal crests. When distended, lacrimal sac is about
15 mm in length and 5-6 mm in breadth. It has got
three parts: fundus (portion above the opening of
canaliculi), body (middle part) and the neck (lower
small part which is narrow and continuous with the
nasolacrimal duct).
4. Nasolacrimal duct (NLD). It extends from neck of
the lacrimal sac to inferior meatus of the nose. It is
about 15-18 mm long and lies in a bony canal formed
by the maxilla and the inferior turbinate. Direction of
the NLD is downwards, backwards and laterally.
Externally its location is represented by a line joining
inner canthus to the ala of nose. The upper end of the
NLD is the narrowest part.
There are numerous membranous valves in the
NLD, the most important is the valve of Hasner, which
is present at the lower end of the duct and prevents
reflux from the nose.