Lacrimal gland and tear drainage Flashcards
Where are tears produced?
Lacrimal gland and accessory lacrimal tissues
How does congenital nasolacrimal duct obstruction present?
2-4% of newborns
Presents with tearing and mattering
>90% resolve by 1 year
Of those 10% that don’t improve, probing cures 95%
What are the common congenital and canalicular abnormalities?
Imperforate puncta
Absent puncta
Punctal and canalicular atresia
Can involve upper and lower
Where is the lacrimal gland/sac found?
Superolateral aspect of orbit in lacrimal fossa (anteriorly has thick maxillary bone, posteriorly has thin lacrimal bone)
anterior part of medial orbit in lacrimal sac fossa
What is the significance of the posterior lacrimal crest?
Lacrimal bone
Posterior extent of lacrimal sac fossa
Deep/posterior portion of medial canthal tendon inserts here
How does the lacrimal bone density vary?
Thicker posterior to posterior lacrimal crest
Significant in DCR as incision into nasal cavity should be through the anterior part of lacrimal bone where it is thinnest
Where does the nasolacrimal duct run?
Begins as an opening in the inferoanterior orbital floor
Descends through maxillary bone
Passes posteriorly and laterally towards first molar tooth
What are the three layers of the tear film?
Lipid layer
Aqueous layer
Mucinous layer
What are the two lobes of the lacrimal gland?
Orbital lobe (superior and larger)
Levator palpebrae superioris lies inbetween
Palprebral lobe
How big is the lacrimal gland?
20x 12 x 5mm
Orbital lobe
Palprebral lobe (1/4 of total size)
What are the anatomic relations of the lacrimal gland?
Orbital : posterior to orbital septum and preaponeurotic fat pad. Anterior to levator aponeurosis
2-6 ducts travel through orbital part into palpebral part where they form 6-12 ducts which drain into the superolateral conjunctival fornix
Therefore, removal of palpebral portion renders the entire gland non functional
Describe the histology of the lacrimal gland
Compound tubuloacinar gland (serous type)
Composes of lobules
Each lobule contains numerous acini
Each acinus is a single layer of cuboidal or columnar cells
Stellate shapes myoepithelial cells surround each acini
What are the two types of accessory lacrimal gland?
Glands of Krause
Glands of Wolfring
Where are the glands of Krause?
20-40 in superior conjuntival fornix and half that in the lower eyelid.
WHere are the glands of Wolfring?
Superior tarsal border
Under sympathetic stimulation
Baseline tear production
What is the blood supply to the lacrimal gland?
Lacrimal artery (branch of ophthalmic artery) with contributions from infraorbital artery and recurrent meningeal artery
What is the nerve supply of lacrimal gland?
V1 ophthalmic nerve-> frontal nerve-> lacrimal nerve
Runs on top of superior rectus to supply gland
Pierces septum and supplies upper lid and conjunctiva
Parasympathetic sphenopalatine ganglion
Descending autonomic pathways from hypothalamus influence lacrimal system
When does reflex crying occur?
Irritation of cornea, conjunctiva and nasal epithlium
Describe the excretory system?
Eye lids Puncta Canaliculi Lacrimal sac Nasolacrimal duct Nose
How do eyelids affect tears?
Eyelids move the tears across the eye from lateral to medial
As we age, the eyelids sag which can cause eye watering
How does the medial insertion of orbicularis oculi assist with lacrimal function?
Orbicularis oculi inserts medially which encases the lacrimal sac
Horner’s muscle (deep head of preseptal orbicularis oculi) contributes to lacrimal pump and moves eyelids medially
Provides active passage of tears during blinking
Describe the movement of tears from the tear meniscus to lacrimal sac
Both active and passive
Passive: gravity and capillary action
Active: medial canthus blinking. When eyelids close the puncta meet, squeezing the tears already in the ampulla, pushing them into the horizontal portion of duct
Describe the puncta
0.1-0.2mm diameter
Surrounded by ring of fibrous tissue
Lacrimal papillae are surrounded by orbicularis oculi fibres creating a tiny sphincter
Can close by meeting other puncta or individually by its own sphincter -therefore surgically important not to damage the puncta by cutting it open
Describe the caniliculi
Short vertical 2mm
Longer horizontal 8-10mm
Lower longer than upper
Curve posteriorly and medially towards lacrimal sac
Pass behind medial canthal tendon and meet at an angle 25 degrees forming the common canaliculus
Does everyone have a common canaliculis?
90% of adults
2% completely separate upper and lower canaliculi
What are the two distinct parts of the lacrimal sac?
Portion 3-5cm above common opening= fundus
Portion9-12cm below common opening =body
Describe the histology of the lacrimal sac
Fibroelastic tissue arranged in a helical pattern
Lumen lined by non keratinized stratified columnar epithelium
Why does the lacrimal sac expand laterally and anteriorly as it enlarges (eg in mucocoele)?
Below the medial canthal tendon, the sac is only covered by lacrimal fascia, orbicularis oculi and skin
The tendon and sac limit superior sac expansion
What is the blood supply of the lacrimal sac?
Ophthalmic artery: dorsalis nasi, medial palpebral artery External maxillary artery: angular branch of the facial artery Internal maxillary artery: Infraorbital branch
What is the nerve supply of the lacrimal sac?
Infratrochlear branch of nasociliary nerve
Which other duct is the lacrimal sac continuous with?
Nasolacrimal duct lies inferior and is continuous with lacrimal sac
It runs posteriorly in relation to the nasal canal
What is the name for the inferior opening of the nasolacrimal duct into the nose?
Valve of hasner
What is the embryological origin of the lacrimal gland?
Ectodermal buds invade underlying mesenchyme
10th week: tendon of LPS develops
Tears begin 3 months after birth
Development of gland continues until 3-4 years old
What is the sympathetic nerve supply to the lacrimal gland?
From superior cervical ganglion
Travel through sphenopalatine ganglion (but do not synapse)
Joins maxillary nerve
Then lacrimal nerve
What are the two different types of mucin present in the mucoid layer of the tear film?
Muc1/4: maintains hydration of ocular surface +stabilises tear film
MUC5AC: traps pathogens and debris to be cleared by blinking
What is contained in the aqueous layer of the tear film?
Secreted by lacrimal and accessory lacrimal glands
Contains water, electrolytes, lysozymes (eat bacteria) and lactoferrin (eats iron)
What is contained in the lipid layer of the tear film?
Secreted by meibomian glands
Prevents evaporation of tear film and smooth ocular surface during blinking
What is posterior blepharitis?
Meibomian gland dysfunction
Risk factors; age, smoking, associated with rosacea
Presents with dry eye symptoms and oily Meibomian glands visible
Inferior staining with lisssamine green is suggestive of incomplete blink
Treated with warm compress, doxycycline and omega 3 supplements
