lacrimal apparatus: basic anatomy and physiology
Post on 22-Jan-2018
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Dr Sabin Sahu
MS Ophthalmology
SCEH. Lahan
Lacrimal Apparatus The lacrimal apparatus include structures concerned
with:
a) Formation of tears - Lacrimal gland
b) Drainage of tears - Lacrimal passage
The lacrimal passage include: puncta, canaliculi, lacrimal sac and nasolacrimal duct (NLD)
Diagram of lacrimal apparatus
Lacrimal gland Main Lacrimal gland
Location - in the superior lateral quadrant of the orbit within the fossa for lacrimal gland
Parts – superior orbital part and inferior palpebral part
Ducts – 10 to 12 ducts of lacrimal gland open into the superior fornix
Blood supply – lacrimal artery, a branch of ophthalmic artery
Nerve supply – lacrimal nerve, a branch of ophthalmic division of fifth cranial nerve
Accessory lacrimal glands
These include - Glands of Krause, Glands of Wolfring
Lacrimal passages1) Lacrimal puncta
Two small round or oval openings one each on the upper and lower eyelid
It is located at the posterior edge of the lid margin
Normally they face slightly posteriorly and can be inspected by everting the medial aspect of the lids.
2) Lacrimal canaliculi
Parts : Vertical part – 2 mm (ampullae) and
horizontal part - 8 mm
The superior and inferior canaliculi usually (>90%) unite to form the common canaliculus, which opens into the lacrimal sac.
A small flap of mucosa (Rosenmüller valve) at the junction of the common canaliculus and the lacrimal sac prevents reflux of tears into the canaliculi.
3) The lacrimal sac
It is 10–12 mm long and lies in the lacrimal fossa
The lacrimal bone and the frontal process of the maxilla separate the lacrimal sac from the middle meatus of the nasal cavity.
Parts: fundus (portion above the opening of canaliculi), body (middle part) and
neck (lower part opening into nasolacrimal duct)
In a dacryocystorhinostomy (DCR) an anastomosis is created between the sac and the nasal mucosa to bypass an obstruction in the nasolacrimal duct.
4) The naso-lacrimal duct
It is 12–18 mm long and is the inferior continuation of the lacrimal sac.
It is directed downwards, outwards and backwards.
Parts: intraosseous part and intrameatal part
It opens into the nasal cavity in the inferior nasal meatus
The opening of the duct is partially covered by a mucosal fold (valve of Hasner).
Physiology About 10% of tear elimination occurs by evaporation in
young and about 20% in elderly person
Most of the tear is actively pumped from tear lake by lacrimal pump mechanism
Lacrimal pump mechanism
Brought about by preseptal fibres of orbicularis oculimuscle (Horner’s muscle)
On eyelid closing
Contraction of preseptal fibres of orbicularis (Horner’s muscle) pulls the lacrimal fascia and wall of lacrimal sac Opens the lacrimal sac create negative pressure draws tears from canaliculi into lacrimal sac
When the eyelid opens
Relaxation of preseptal fibres of orbicularis (Horner’s muscle) Allows the lacrimal sac to collapse create positive pressure expels fluid downwards into nasolacrimal duct
Lacrimal pump mechanism
Syringing Procedure:
1. Topical anaesthesia - 4 per cent Xylocaine drops
2. Lower punctum is dilated with a punctum dilator
3. Normal saline is pushed into the lacrimal sac through the lower punctum with the help of a syringe and lacrimalcannula
Results are interpreted as follows:
a) A free passage of saline through lacrimal passages into the nose no obstruction or partial obstruction.
b) Regurgitation of purulent fluid from upper punctum, sac fills up obstruction in nasolacrimal duct
c) Regurgitation of clear fluid from upper punctum, sac doesn’t fill up, no fluid pass into nose common canaliculi block
d) Immediate reflux of the saline through the lower punctum, no fluid pass into nose lower canalicularobstruction Under these circumstances the procedure should be repeated
through the upper punctum.
A free passage of saline into the nose will confirm the blockage in the lower canaliculus while regurgitation back through the same punctum will indicate block in both canaliculus.
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