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OpAnatomy > Lacrimal > Flashcards

Lacrimal Flashcards

(47 cards)

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1
Q

What are the three components of the lacrimal system?

A

secretory, distribution, elimination

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2
Q

what does decretory system of lacrimal system do?

A

produce majority of tear fluid - aqueous
divided into 2 portions/lobes by levator aponeurosis - orbital lobe and palpebral
lobes connected by ducts to open into conjunctival fornix.

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3
Q

What is a tubulo-acinar gland? What is the relationship to intralobular ducts?

A

Tubulo-acinar gland contain many acini (clusters of secretory cells) which join to form intralobular ducts.

Intralobular ducts then drain the lacrimal gland into the surface of the eye.

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4
Q

What is the purpose of the accessory lacrimal glands and where are they located?

A

The accessory lacrimal glands produce 10% of the aqueous production
Krausse - fornix
Wolfring – along orbital margin of tarsal plate

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5
Q

How is the lacrimal gland innervated?

A

Autonomic input
Parasympathetic
Sympathetic
Sensory input
Via lacrimal nerve (branch of trigeminal nerve)

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6
Q

What are anatomical structures surrounding the lacrimal sac?

A

Horner’s muscle and medial palpebral ligament surround the lacrimal sac. When horner’s muscle contracts, pushes tears out of lacrimal sac past the Hassner’s valve

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7
Q

What is the importance of the hydrophilic nature of mucins?

A

Helps to wet the ocular surface

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8
Q

What are the functional roles of the tear film?

A

Osmotic boundary – maintaining corneal hydration
Gas, nutrient, and waste solvent for exchange with avascular cornea
Optical Boundary
Lubricant
Protection - antimicrobial

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9
Q

How do you maintain tear film stability?

A

temperature, humidity, gland outputs and blink rates

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10
Q

What is a result from lack of tear film stability?

A

Short tear film break up time
Keratoconjunctivitis Sicca (dry eye)

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11
Q

What are the reasons for tear secretion?

A

Basic secretion
No obvious external stimuli
Reflex secretion
Tear production when external stimuli lead to c
increased tear production (irritation)
Emotional/psychogenic secretion

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12
Q

Discuss the three components of the tear film and secretions?

A

Mucin
Goblet cells in conjunctival epithelium – stored in
secretory granules within goblet cells (crypts of
Henle – pockets of mucin secreting cells present)
Maintain hydration and lubrication of cornea and
conjunctiva, protect ocular surface by coating
foreign bodies and helps wet ocular surface
(hydrophilic)
Aqueous
Secreted by lacrimal gland (accessory glands of
krausse and wolfring)
Makes bulk of tear film, maintains pH and
osmolaritiy of tears, provides oxygen and
nutrients and waste removal for cornea and
antibacterial components
Lipid
Secreted by meibomian glands (zeis and moll)
Reduces evaporation stabilising tear film, prevents
overflow of ears, smooth optical surface, prevents
contamination of tear film by skin lipids

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13
Q

What is the difference between basic and reflex secretions?

A

Reflex Secretions
Due to external stimulus (initiates neural signals)
Increases tear production
Can produce up to 100x tear volume
Main secretors of lacrimal gland – main lobe and
accessory lobe
Basic Secretions
Natural secretory
No obvious external stimuli

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14
Q

What are the microscopic components of the lipid layer of the tear film?

A

Hydrophobic outer layer protects water from escaping as non-polar

Hydrophilic inner layer bonds to the aqueous component (polar)

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15
Q

What are the microscopic components of the aqueous layer of the tear film?

A

Water
Electrolytes
Proteins

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16
Q

What are the microscopic components of the mucin layer of the tear film?

A

No distant division between aqueous and mucin
Two phase – one with more mucin the other with less mucin
Glycocalyx is the glycoprotein layer attached to the surface epithelium cells (stratified squamous cells of cornea and conjunctiva)

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17
Q

More about the glycocalyx

A

Glycoprotein present in membrane bound vesicles within the epithelium cells that fuse to the cell membrane to release the glycocalyx
Contributes to the wetability of the epithelium surface cells and bonds the mucin layer to the epithelium
Surface area for bonding increased by epithelium microvilli

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18
Q

What is the thickness of the tear film?

A

2-5um
Decreases rapidly after blinking

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19
Q

How much tear fluid it produced and how fast?

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A

Tear volume – 1ul
Tear prism (meniscus) – 4ul
Rate 1.2ul/min
Turnover 16%/min

20
Q

How can age effect tear fluid volume?

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A

Lacrimal gland innervation not always complete at birth – 87% of newborns show reflex tearing at blink – 95% show within one week

Infants have increased tear film stability – potentially due to increased thickness of the lipid layer

Secretion decreased in old age – reduced tear film stability

21
Q

What does pilocarpine do to tear volume?

Study These Flashcards
A

Increases the flow (parasympathomimetic)

22
Q

What does atropine do to tear volume?

Study These Flashcards
A

Decreases flow (parasympatholytic)

23
Q

What other drugs decrease tear production?

Study These Flashcards
A

Diuretics
Antihistamines
Antidepressants
Antianxiety medications

24
Q

What are the electrolytes in the tear film and what are they responsible for?

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A

Na+
Cl-
K+
HCO3-
Ca++
Mg++
Responsible for pH and osmolarity of tears

25
What are the major proteins in the tear film and their purpose?
Lysozyme Antibacterial – dissolves bacterial wall Secretory IgA Antibody – important in immunological defence Lactoferin Antibacterial – iron binding protein Lipocalin Thought to contribute to stability of lipid layer Albumin Concentration increases in inflammation Ig Concentration increases in inflammation
26
What are the regulated proteins? Which protein is contitutive?
Lactoferin Lipocalin Lysozyme Secretory IgA
27
What does hypoxic stress do to the cornea?
Makes it swell
28
What is another metabolite of the tear film?
Glucose Source in blood Given to cornea as avascular
29
What happens to osmolarity after prolonged eye closure? What about dry eye?
Osmolarity is decreased as there is more water (less evaporation) Dry eye – osmolarity increases as there is more evaporation – more solutes on the eye
30
What is the normal range for pH of the tear film and why would it be low in a normal patient?
The normal range is 7.14-7.82 (about 7.45) Generally lowest after waking due to acidic bi-products of anaerobic respiration
31
Explain the Holly and Lemp model for stability of the tear film
Based upon the lipid mucin interaction After blink, hydrophobic lipid layer separated from hydrophilic mucin layer by aqueous layer – tear film thins At certain critical thickness – hydrophobic lipids contaminate small areas of the mucous phase Contaminated mucin layer cannot support aqueous resulting in break up
32
Explain the Sharma and Ruckenstein Model for stability of the tear film
Based on mucin dispersive forces Influences of short range intermolecular interactions: two steps After blink, thinner mucus at tips of microvilli begins to thin Aqueous phase contacts epithelial surface – cannot support aqueous phase
33
Explain the Fatt (McDonald and Brubaker) model for stability of the tear film
Meniscus induced thinning of tear film Explains tear film break up occurring near eyelid margins
34
What additives and substitutes can be used observing the tear film and what do they do?
Fluorescein Observing tear film Well stain damaged cells and accumulates in intercellular spaces resulting from discontinues in epithelium Rose Bengal Stains dead and devitalised muscous Lissamine Green Stains dead and devitalised cells Stains mucous
35
what is dry eye
Multifactorial disease of the tears and ocular surface that results in Symptoms of discomfort Visual disturbance Tear film instability Potential damage to the ocular surface accompanied by increased osmolarity of the tear film and inflammation of the ocular surface
36
What is aqueous tear deficiency and what are the types and their descriptions?
Lacrimal gland and accessory gland not producing sufficient tears Sjogren’s syndrome Progressive auto-immune disease associated with severe aqueous tear deficiency (also affects saliva glands – dry mouth, and associated with Rheumatoid arthritis) Typically affects older female patients Non-Sjogren’s Lacrimal gland disease Lacrimal duct obstruction Reflex
37
What is Evaporative issues with the tear film and what causes it?
Quantity of tears produced is normal, BUT tears produced evaporate excessively Lipid deficiency Meibomian gland dysfunction, blepharitis Surface changes Mucin deficiency
38
What other outer anatomical feature can cause dry eye?
Lid anomaly Blinking Lid surface incongruity
39
What is the prevalence of dry eye and the different types?
Dry eye prevalence ~5-30% Prevalence greater with older age and in females Evaporative dry eye more common than aqueous deficient Estimated prevalence of Meibomian gland dysfunction >60% in some older populations
40
How can tear quantity be tested and what are general values?
Schirmer test <5mm in 5min sign of dry eye >10mm normal Phenol thread test <10mm in 15sec suspicious of dry eye Tear meniscus height Usually >0.3mm <0.1mm indicative of dry eye Dye dilution Tear turnover rate reduced in dry eye Fluorescein dye instilled into the eye diluted less with dry eye patients
41
How can tear quality be tested and what are general values?
Fluorescein break up time Instill fluorescein into eye – patient blinks – observe tearfilm for breakups (dark spots in fluorescein) Time taken for tearfilm to break up = fluorescein break up time <10secs indicative of dry eye Non-invasive break up time Estimation from observation of reflection from ocular surface – discontinues in reflection show break up Majority >20sec Lipid layer observation (some evidence between showing lipid layer thickness and meibomian gland dysfunction) Less ferning present when tested (mucous ferning)
42
What is the osmolarity of normal and dry eyes?
Normal <312mOsm/kg Dry eye >323mOsm/kg
43
What is conjunctival hyperaemia?
Dry eye will cause inflammation of ocular surface General sign of ocular surface inflammation
44
How does dry eye affect goblet cells?
Goblet cell density decreases
45
How do you examine dry eye?
Order of testing for least invasive to most invasive test Examine lids for blepharitis Examine meibomian glands for dysfunction Evaluate tear meniscus and tear film Measure break up time Observe fluorescein or rose bengal staining
46
How do you manage dry eye?
Tear substitutes Ointment Lipid Sprays Evaporation control Reduce drainage: punctal occlusion Meibomian gland care (hygiene, antibiotics, omega 3)
47
How can you treat meibomian gland disease?
Lipiflow Applies heat and pressure to the eyelids Evidence of improvement in signs and symptoms of MGI after a single treatment Blephasteam Goggles that warm lids to treat meibomian gland dysfunction Evidence of improvement in symptoms of dry eye

OpAnatomy (9 decks)

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