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Physiology of the Eye > Tear Production and Drainage (Gelatt 5) > Flashcards

Tear Production and Drainage (Gelatt 5) Flashcards

1
Q

How does the preocular tear film maintain an optically uniform corneal surface?

A
  • smoothing out minor irregularities
  • removing foreign matter from the ocular surface
  • lubricating ocular surface
  • provides nutrients to the cornea
  • controls local bacterial flora (some species)
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2
Q

What is the tear turnover rate in humans?

A

1.03 +/- 0.39 uL/min

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3
Q

What is the tear evaporation rate in humans?

A

0.14 +/- 0.07 uL/min

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4
Q

What is the thickness of the outer lipid layer of the tear film?

A

~0.1 uM

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5
Q

Characterize the components of the lipid layer, and what are their functions.

A

compounds called long chain (o-acyl)-omega-hydroxy fatty acids. These are unsaturated and branched-chain fatty acids and alcohols, 8-32 carbon chains in length. They appear to aid in tear film stability and prevention of deterioration.

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6
Q

What glands produce the lipid layer of the tear film, and what type of secretion do they undergo?

A
  • sebaceous glands (tarsal and Meibomian)

- they undergo holocrine secretion.

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7
Q

What two compounds may play a role in meibomian gland secretion?

A

adrogens and neurotransmitters

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8
Q

Androgen receptor mRNA has been isolated from the Meibomian glands of what species?

A

rat
rabbit
human

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9
Q

What neuropeptides have been associated with Meibomian glands in humans and guinea pigs?

A
  • calcitonin gene-related peptide
  • substance P
  • nueropeptide Y
  • vasoactive intestinal peptide
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10
Q

What is the thickness of the middle aqueous layer?

A

~7um (>60% of the total thickness)

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11
Q

What is the middle aqueous layer composed of?

A

98% water and 2% solids (predominantly proteins)

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12
Q

What compounds are found int he middle aqueous layer?

A
  • inorganic salts
  • glucose
  • urea
  • proteins
  • glycoproteins
  • soluble muxins
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13
Q

What structures contribute to the formation of the aqueous tear layer?

A
  • lacrimal gland
  • gland of the nictitating membrane
  • Harderian gland
  • accessory lacrimal glands in conjunctiva
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14
Q

What are some drugs that can transiently reduce tear production?

A
  • topical anesthetics
  • anticholinergics
  • preanesthetics (ace and ketamine)
  • general anesthesia
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15
Q

What is the thickness of the mucin layer?

A

~0.02-0.05 um

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16
Q

What two components make up the mucin layer?

A
  • mucins

- underlying glycocalyx

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17
Q

What produces the mucin layer?

A
  • apocrine secretions from the conjunctival goblet cells
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18
Q

What is the difference in organization of conjunctival goblet cells between rats/mice and humans/rabbits?

A
  • in rats and mice the goblet cells occur in clusters, where as in rabbits and humans they appears as single cells.
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19
Q

Describe the distribution of goblets cells in the human and dog?

A

They are similar, with densities being highest in the lower nasal and middle fornices. Goblet cells in both species are essentially absent from the bulbar conjunctiva adjacent to the limbus

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20
Q

What two layers of the tear film does the Harderian gland contribute to?

A

aqueous and mucin layers

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21
Q

Characterize the compounds of the mucin layer.

A
  • composed of glycoproteins 20-40 million daltons (MUC1-21)

- the glycoproeteins are carbohydrate-protein complexes with hexosamines, hexes and sialic acid

22
Q

What is the function/importance of the glycoproteins in the mucin layer?

A

they help lubricate the corneal surface and stabilize the tear film by making the hydrophobic corneal epithelium more hydrophilic to allow spreading of the aqueous layer.

23
Q

How does the mucin layer stabilize the tear film?

A
  • they layer lowers the surface tension over the corneal epithelium and permits spreading of the tear film after blinking.
24
Q

What is the tear volume and flow rate in the horse?

A
  • volume of 233.74 uL

- flow rate of 33.62 uL/min

25
Q

What is the tear turnover rate in the horse?

A

approximately 7 minutes

26
Q

What is the average pH of tears?

A

7.5

27
Q

What electrolyte in the tear film is not similar to levels found in plasma?

A

potassium (generally 3-6 times more abundant than in plasma indicating an active transport mechanism)

28
Q

How do levels of glucose in the tears and plasma correlate?

A

glucose is typically lower in the tears than in plasma, however the levels do correspond to one another (when plasma levels rise, tissue fluid levels also rise, which increases glucose levels in the tear film) does not come from lacrimal gland secretions

29
Q

What device could be potentially used to measure glucose levels in the tears?

A

amperometric electrochemical sensor

30
Q

What are the nonspecific antimicrobial substances of the tear film?

A
  • lysozyme
  • lactoferrin
  • a-lysine
  • complement
31
Q

What are the specific antimicrobial substances of the tear film?

A
  • secretory immunoglobulins A, G, M

- Toll-like receptors (expressed by corneal and conjunctival epithelial cells)

32
Q

What is the average protein level in the canine tears?

A

0.35g/dL

33
Q

What are the proteins found in the canine tears, and what are their relative percentages?

A
  • globulins (93%)
  • albumin (4%)
  • lysozyme (3%)
34
Q

Where is lysozyme produced, and how does it excerpt it’s antibacterial and antifungal effects?

A
  • produced by the conjunctival goblet cells

- hydrolyzes bacterial and fungal cells walls

35
Q

What happens to the level of lysozymes in conjunctivitis?

A

increase

36
Q

What are the levels of lysozymes in domestic animals relative to humans and non-human primates?

A

domestic species typically have lower levels of lysozymes in tears (horses have 1/2 to 1/4 that found in humans) and cats have none.

37
Q

How does lactoferrin exert it’s antibacterial effects?

A

binds iron needed for bacterial metabolism and growth.

38
Q

Which immunoglobulin is found in greatest concentrations in the tear film?

A

Immunoglobulin A

39
Q

How do immunoglobulins exert their antimicrobial effects?

A

they coat bacterial and viral microorganisms, leading to agglutination, neutralization, and lysis

40
Q

What is the lacrimal nerve a branch of, and what does it supply to the tear film?

A
  • branch of the trigeminal nerve

- provides sympathetic and parasympathetic nerve fibers to the lacrimal gland

41
Q

What are the neurotransmitters supplied by the parasympathetic fibers of the lacrimal nerve?

A

acetylcholine and vasoactive intestinal peptide

42
Q

What are the neurotransmitters supplied by the sympathetic fibers of the lacrimal nerve?

A

norepinephrine and neuropeptide Y

43
Q

Describe the adrenergic and cholinergic distribution patterns surrounding the lacrimal gland blood vessels and acinar cells?

A

cholinergic fibers appear in greater numbers.

44
Q

Stimulation of the cholinergic and adrenergic fibers supplying the lacrimal gland leads to what?

A

secretion of proteins into the lacrimal fluid via multiple cellular pathways in a process known as signal transduction.

45
Q

What are the 4 types of tears reported in humans?

A
  • basal
  • reflex tears
  • pharmacologically induced tears
  • psychogenic or emotional tears
46
Q

Humans with KCS are deficient in what types of tears (of the 4 types)?

A

basal and reflex

47
Q

What are the levels of lysozyme and lactoferrin in human patients with KCS.

A

decreased compared to normal patients.

48
Q

Basal tear levels in dogs and cats account for what percentage of total tear formation?

A

50% (therefore a Schirmer 2 test should be decreased by 50% comported to a Schirmer 1)

49
Q

Characterize movement of tears into the lacrimal puncta and through the nasolacrimal system.

A

Pooled tears in the palpebral fissure are drawn into the lacrimal puncta via capillary action when the facial muscles relax. This is also facilitated by normal breathing movements. Reflex blinking closes the lacrimal sac, acting as a pump to move tears through the system. Psuedoparastaltic motion moves tears into the nasal cavity.

50
Q

In the dog, which puncta is the most important for tear drainage?

A

Lower

Physiology of the Eye (10 decks)

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