lacrimal system

Question 1

What are the structures in the tear production system

Answer 1

Lacrimal gland, accessory glands of krause and wolfring, sebaceous/ meibomian/ tarsal glands, goblet cells, glands of zeiss and moll

Question 2

what are the two systems in the lacrimal system

Answer 2

Tear production input (secretory) and tear drainage Output (excretory)

Question 3

Where is the lacrimal gland

Answer 3

Superior temporal quadrant of the orbit

Question 4

What does the lacrimal gland consist of

Answer 4

Large orbital part and small palpebral part

Question 5

Where is the description of the orbital part

Answer 5

Almond shaped structure in the lacrimal gland fossa, beneath the frontal bone, just above the LPS

Question 6

Where is the description of the palepebral part

Answer 6

Beneath the aponeurousios of LPS and lies in the upper eyelid at the conjunctival fornix

Additional ducts from the palpebral part open into the superior fornix

Question 7

Name the accessory glands of tear production and their location

Answer 7

Glands of Krause and Wolfring (stroma of palpebral conjunctiva)

Glands of Molls and Zeis (located behind and between lash follicles)

Meibomian gland (tarsal plate of eyelid)

Goblet cells (located in conjunctiva)

Question 8

What spreads uniformly across the cornea by blinking, and is held in place by surface tension

Answer 8

Pre corneal Tear Film (PCTF)

Question 9

What is the function of the PCTF

Answer 9

• Provides a smooth and uniform first optical refractive surgace of the first optical refractive surface of the eye
• Keep the cornea wet at aall time to prevent desiccation
• Second line of defence for the eye (first line of defence is eyelash)

Question 10

What is the composition of the PCTF

Answer 10

Outermost layer (exposed to air) - lipid or oily layer

Middle layer (aqueous or watery layer)

Innermost layer (mucous layer)

Question 11

What is the lipid layer of the PCTF secreted by

Answer 11

Meibomian glands, glands of Zeis and Moll

Question 12

What is the function of the lipid layer

Answer 12

• Protective hydrophobic layer
• Reduce evaporation of underlying aqueous layer
• Prevents spillage of tears from the lid margin

Question 13

What is the aqueous laye secreted by

Answer 13

• Lacrimal gland (orbital and palpebral), reflex secretion
• acessory glands of Krause (conjuncitval fornices), basal secretion
• accessory glands of Wolfring (conjuctival tarsus), basal secretion

Question 14

What is the composition of the aqueous layer

Answer 14

Lysozyme, immunoglobin, beta lysin, amino acids, metabolites, electrolytes

Question 15

What is the function of the aqeuous layer

Answer 15

• Enables gaseous exchange
• Flush away noxious substances
• Exit pathway for debris and desqaumated epithelial cells
• Provides a delivery route for immunologic cellular response (white blood cells) and immunoglobulins to corneal epithelium
• Antibacterial acitivty: contains lysozyme
• Hydrating medium for corneal epithelial cells, carries metabolites to them
• Lubricate at the lid-globe interface to reduce friction when blinking

-PCTF slighty hypertonic to control corneael dehydration state

• Delivery of vitamin A from lacrimal gland to cornea

Question 16

Where is the mucous layer thickest

Answer 16

Thickest at the conjunctiva (2-7um) compared to the cornea (0.4-1 um)

Question 17

What secretes the mucous layer

Answer 17

Conjunctival goblet cells

Question 18

What is the function of the mucous layer

Answer 18

• Decreases surface tension of the tear film by forming a hydrophillic coating over the hydrophobic corneal epithelium
• Hydrates the underlying corneal epithelial cells
• Provides the foundations for a smooth optical surface by covering the irregular corneal surface
• Lubricates the ocular surface and reduces lid-globe friction during blinking

Question 19

What is the afferent pathway of tear secretion

Answer 19

Lacrimal nerve, branch of opthalmic division of trigeminal (CN V) supplies the lacrimal gland with sensory nerve

Question 19

State the two types of Tear secretion for the efferent pathway

Answer 19

Tear secretion, parasympathetic (reflex tearing), sympathetic (basal secretion)

Question 19

What percentage does basal and reflex tearing make up

Answer 19

Reflex tearing (parasympathetic) : Makes up 95% of aqueous component of tears

Basal tearing (sympathetic) : 5% of aqeuous component of tears

Question 20

What causes reflex (parasympathetic) tearing

Answer 20

Central sensory origin
- associated with foreign particle, vomiting, coughing, yawning
- retina (varrying intensity of light)
- psychogenic aka emotional

peripheral sensory origin
- stimulation of CN V in cornea, conjunctiva, nasal, mucousal, skin

Question 21

What does tear secretion, sympathetic innervation do

Answer 21

Regulates blood flow to the lids and conjunctiva and the gland, indirectly influcing secretion

Question 22

What gland(s) provide reflex tearing

Answer 22

Lacrimal gland

Question 23

What gland(s) provide basal tearing

Answer 23

• Accessory lacrimal glands of Krause and Wolfrin (aqueous)
• Mucus gland (goblet cells)
• sebaceous glands (meibomian, zeis n moll)

Question 24

What is the blood supply to the lacrimal gland

Answer 24

Lacrimal artery and infraorbital artery

Drainage into the opthalmic vein

Question 25

Percentage of different types of tear drainage

Answer 25

• 25% lost via evaporation
• 75% drain by nasolacrimal excretory system (puncta, canaliculi, lacrimal sac and nasolacrimal duct)

Question 26

What is the holly lemp mechanism of tear film stabilty

Answer 26

Tear film thins unifomly by evaporation, when the tear film has reached a critical thickness a number of lipid molecules begin to be attracted by the mucous layer and migrate down to this layer

Eventually hwen enough lipid molecules has contaminated it, the mucous layer becomew hydrophobic and the tear film ruptures

Blinking will repair the rupture by removing the lipid contaminant from the mucous layer and restore a thick aqueous layer

Question 27

What is the alternative theory of tear film stabilty

Answer 27

Thinning of aqeuous layer via evaporation, reduces the tensile strength of the aqueous layer to a point where the suction forces from the tear film meniscus at the upper and lower lids would break the thin water film

Question 28

What are the three ways tears are conducted to the lacrimal puncta (not that impt)

Answer 28

Gravity, at the lateral canthus to form the inferior menicus

Capillary attraction: Attraction of tear into the lacrimal puncta na dvertical canaliculi

Lid action: With each blink the tears moves towards the puncta, zipper-like actrion due to the firm attachmenet of the orbicularis oculi at its medial ligament

Question 29

The Jone’s Lacrimal Pump Theory

Answer 29

Orbicularis Oculi contract:
- Punctum drawn nasally
- Ampulla compressed
- Horizontal canaliculi shorten
- Pull on lateral wall of lacrimal sac, pumping tears into sac

Orbicularis Oculi relax:
- Lacrimal sac collapses
- Tears drawn down nasolacrimal duct

Question 30

Explain Doane’s modle of tear drainage

Answer 30

Orbicularis oculi relax:
- Tears drawn into puncta by capillary action and expansion of canaliculi as eyelids open
- Tears go into canaliculi and into lacrimal sac

Orbicularis oculi contract:
- Canaliculi compressed
- Tears drawn towards lacrimal sac
- Lacrimal sac compression
- Tears expelled into nasolacrimal duct