The Lacrimal Apparatus

It consists of the secretory portion and collecting portion. the secretory portion is composed of the lacrimal gland. The collecting portion consists of canaliculi with their orifices (puncti), the lacrimal sac and lacrimal duct which has its opening in the inferior nasal meatus.

The secretory portion

• The lacrimal gland is the main secretory gland and is located on the anterior lateral portion of the roof of the orbit in the lacrimal fossa.
• It is divided into two parts :-
  • Orbital part – the larger part.
  • Palpebral part – small and consists of only one or two lobules.
  • These two are separated by the aponeurosis of the LPSM.
  • The small palpebral portion is located just above the temporal segment of the superior conjunctival fornix by lacrimal secretory ducts which open by about 10 orifices or so.

NB. Removal or gross injury to the palpebral part of the gland cuts off all the connecting ducts and this prevents the secretion of the entire gland.

Functions of the lacrimal gland

• Production of aqueous part of the tear film
• Production of reflex tear film

Blood supply

• Is by the lacrimal artery, a branch of the ophthalmic artery.
• Venous return is a branch of the ophthalmic vein.

Nerve supply

• Sensory supply comes from lacrimal nerve, a branch of the ophthalmic division of the fifth nerve.
• Sympathetic supply comes from the carotid plexus of the cervical sympathetic chain.

Lymphatic drainage joins with the conjunctival lymphatics to drain into the pre-auricular lymph nodes.

The collecting portion

Puncta

• These are two small, rounded or oval openings on upper and lower lids about 3mm in size and about 6 and 6.5 mm respectively, temporal to the inner canthus.
• The openings are surrounded by relatively dense avascular connective tissue lined by stratified squamous epithelium.

Lacrimal canaliculi

• Superior and inferior canaliculi 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 two canaliculi 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.

Lacrimal sac

• It is located in the medial portion of the orbit along the maxillary bone below the medial palpebrae ligament.
• When distended, lacrimal sac is about 12–15mm in length and 5–6 mm in breadth with a volume of about 2 cc.
• 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).

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.
• Numerous membranous valves are present 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.

Tear production and drainage

• Tears produced form a tear lake by active action. They drain into puncta, to canaliculi and then lacrimal sac and lastly to the nasal lacrimal duct.
• Tears are directed into the punctum by capillary attraction, gravity and by the blinking action of the eye lid.
• The combined forces of capillary attraction in the canaliculi, gravity and pumping action of the extension of the orbicularis oculi muscle to a point behind the lacrimal sac all tend to continue the flow of tears down the NLD into the nose.

1. Eyes open, tears flow into puncta and canaliculi passively.
2. Eyes closed, palpebral portion of orbicularis oculi muscle contracts, pulls lacrimal sac open creating a vacuum. Tears are then sucked from the canaliculi into the sac (blinking reflex) hence the lacrimal bulging.
3. Eyes open, orbicularis oculi muscle relaxed leading to collapse of the lacrimal sac forcing the tears to drain into the NLD.