Lacrimal System Flashcards
Which structure secretes the majority of the tear film?
Lacrimal gland.
Which system facilitates the drainage of tears?
Nasolacrimal system.
Describe the tear flow pathway.
- Secretion by lacrimal gland onto ocular surface.
- Channeled medially by orbicularis pump mechanism.
- Drainage into nasolacrimal system via the upper and lower puncta.
- Flow through the upper and lower canaliculi into the common canaliculus.
- Common canaliculus -> nasolacrimal sac -> nasolacrimal duct -> inferior nasal meatus.
Which imbalance causes disorders of tearing?
Imbalance between secretion and excretion of tears.
How many layers are in the tear film?
3 layers.
What are the 3 layers of the tear film?
- Mucin layer - deepest.
- Aqueous layer - thickest layer.
- Lipid layer - most superficial and thinnest layer.
What produces the mucin layer (tear film)?
Conjunctival goblet cells.
What is the function of the mucin layer (tear film)?
- Spreads the film evenly.
- Maintains stability on ocular surface.
What produces the aqueous layer (tear film)?
Lacrimal gland.
What is the function of the aqueous layer (tear film)?
Immune function.
What produces the lipid layer (tear film)?
Meibomian gland (sebaceous).
What is the function of the lipid layer (tear film)?
Prevents evaporation of the tear film.
Which is the thinnest layer of the tear film?
Lipid layer.
Which is the thickest layer of the tear film?
Aqueous layer.
What is reflex tearing?
- Common cause of hypersecretion.
- Caused by irritation of the ocular surface.
- A good quality tear film reduces reflex tearing.
What are the two types of lacrimal gland?
- Main.
- Accessory.
Which nerve provides afferent sensory innervation to the lacrimal gland?
CN5 -> CNV1 -> lacrimal nerve.
Which nerve innervates the secretomotor aspect of lacrimation?
CN7 (parasympathetic).
What are the two types of accessory lacrimal gland?
- Krause.
- Wolfring.
What is the function of the accessory lacrimal glands?
Maintain a basal aqueous layer.
Where are Krause glands found?
- Conjunctival fornices.
- More abundant in the upper fornix.
Where are Wolfring glands found?
- Tarsal plate.
- Less numerous but bigger.
Which accessory lacrimal gland is bigger?
Wolfring.
Which accessory lacrimal gland is more abundant?
Krause.
Which glands produce the mucin layer of the tear film?
Glands of Moll and Zeis.
What are Moll glands?
- Modified sweat glands.
- Apocrine.
What are Zeis glands?
- Sebaceous glands.
- Holocrine.
What type of gland are Meibomian glands?
Holocrine.
Describe Schirmer’s test.
Filter paper placed under lower lid and amount of moisture is measured after 5 mins.
Describe the interpretation of Schirmer’s test.
- > 10mm is normal.
- <5mm is tear deficiency.
Describe the tear film break-up time.
Eye is stained with fluorescein dye and the time taken for the first dry spot to appear on the cornea is measured.
Describe the interpretation of the tear film break-up test.
- <5 seconds - abnormal tear film.
- 10-30 seconds - normal.
Describe the Jones 1 test.
Dye is squirted onto the conjunctiva and cotton bud is placed in the inferior meatus.
Describe the interpretation of the Jones 1 test.
- If dye on cotton bud - normal.
- If no dye on cotton bud - do Jones 2.
Describe the Jones 2 test.
Dye syringed into the nasolacrimal system and cotton bud placed in the inferior meatus.
Describe the interpretation of the Jones 2 test.
- No dye on cotton bud - nasolacrimal system obstruction.
- Dye is now seen on cotton bud - pump/punctal problem.
What is dacryocystography?
Radiological evaluation using injected fluorescent contrast to evaluate the nasolacrimal system morphology.
What are the pros and cons of dacryocystography?
Pro:
- Excellent anatomical detail for evaluation.
Con:
- Invasive and painful.
What is dacryoscintigraphy?
Radiological evaluation of nasolacrimal system drainage using radiopharmaceutical eyedrops.
What are the pros and cons of dacryoscintigraphy?
Pro:
- Painless.
Con:
- Evaluation of tear flow but provides poor anatomical detail.