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Ocular Physiology > Block 12 > Flashcards

Block 12 Flashcards

1
Q

What is the simplified cause of glaucoma?

A

Aqueous flow in does not equal flow out

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2
Q

What is the unconventional pathway?

A

Aqueous moves through the ciliary muscle and other downstream tissues

It is minor (5-35%)

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3
Q

What is the conventional pathway?

A

Aqueous moves through the trabecular meshwork and Schlemms canal

It is major (65-95%)

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4
Q

Where all does aqueous flow in the unconventional pathway

A

AH enters the connective tissue between the ciliary muscle bundles, through the suprachoroidal space, and out through the sclera

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5
Q

Is the unconventional pathway affected by IOP

A

NO

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6
Q

How does unconventional pathway change with age

A

It decreases

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7
Q

In the conventional pathway where does aqueous flow?

A

Through the TM across Schelmms canal, into its lumen and into the draining collector channels, aqueous veins, and episcleral veins

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8
Q

What are the 2 models for conventional pathway

A

Bulk flow model

Pumping Model

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9
Q

Is the conventional pathway affected by IOP

A

YES

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10
Q

What is the Bulk Flow model of conventional aqueous flow

A

Change n pressure=IOP-EVP

An acute rise in EVP results in a 1:1 ratio of increase IOP

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11
Q

What is the pumping model of the conventional pathway

A

The aqueous outflow pump receives power from the transient increases in IOP such as occur in systole of the cardiac cycle during blinking and during eye movement

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12
Q

An increase in IOP causes what change in drainage?

A

Increase drainage

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13
Q

What happens with very constant high IOP

A

Schlemm’s canal can collapse on itself and obstruct entry into venous system

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14
Q

What is the role of the TM in aqueous flow

A

The TM is suspended between 2 compartments with different pressures

TM can sense the pressure differences and tries to maintain them within a homeostatic range

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15
Q

What are some things that can occlude the angle

A 
Diabetes
Uveitis
Hyphema
Pseudoexfoliative glaucoma
Pigment dispersion glaucoma
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16
Q

How does diabetes occlude the angle

A

Neovascularization from the proliferative diabetic retinopathy

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17
Q

How does uveitis occlude the angle

A

Inflammatory cells and peripheral anterior synechiae

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18
Q

How does hyphema obstruct the angle

A

Blood accumulates in the anterior chamber

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19
Q

How does pseudoexfoliative glaucoma occlude the angle

A

Aging epithelial cells of the iris and lens capsule can release pigment and pseudoexfoliative material

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20
Q

How does pigment dispersion glaucoma occlude the angle

A

Pigment is released from the posterior layer of the iris due to posterior bowing o the iris against the lens zonules

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21
Q

In humans, ____% of the resistance to the aqueous humor outflow is localized to the TM

A

75%

The other 25% occurs beyond Schlemms canal

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22
Q

What is Fuch’s heterochromic iritis

A

Chronic inflammation that can cause permanent TM damage

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23
Q

What is glaucomatocyclitic crisis

A

Acute inflammation of the TM

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24
Q

What are some long term influences on IOP

A

Genetics
Gender
Refractive error

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25
Q

What are short term factors that influence IOP

A 
Diurnal
Postural variation
Lid/eye movement
Systemic conditions
Environmental conditions
Food and drugs
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26
Q

Does genetics affect IOP

A

YES

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27
Q

How does gender affect IOP

A

It is equal between men and women 20-40 yoa

In older ages, there is an increase in IOP with age more in women

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28
Q

How does refractive error affect IOP

A

Positive correlation between IOP and axial length/increased degrees of myopia

Myopic people have a higher incidence of open-angle glaucoma

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29
Q

T/F IOP fluctuates throughout the day

A

True

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30
Q

What is the range of IOP throughout the day

A

3-6 mmHg

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31
Q

When is IOP the highest

A

In the morning hours

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32
Q

How does posture affect IOP

A

Increase when changing from sitting to laying down

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33
Q

T/F patients with systemic hypertension have greater IOP increase after 15 minutes in supine

A

True

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34
Q

How do lids affect IOP

A

Blinking can raise IOP 10 mmHg

Hard squeezing can raise it as high as 90 mmHg

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35
Q

How do eye movements affect IOP

A

Increase in IOP in upgaze

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36
Q

Thicker corneas give…

A

Artificially high readings

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37
Q

Thinner corneas cause….

A

Artificially low readings

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38
Q

How does pregnancy affect IOP

A

It is reduced during pregnancy

Possibly progesterone

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39
Q

How does HIV affect IOP

A

They have lower than normal IOP

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40
Q

Exposure to cold air causes

A

Reduced IOP

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41
Q

How does gravity affect IOP

A

A sudden marked increase in IOP

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42
Q

How does alcohol affect IOP

A

Lowers it

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43
Q

How does caffeine affect IOP

A

Causes a transient rise in IOP

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44
Q

How does tobacco smoking affect IOP

A

It causes a transient increase

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45
Q

How does heroin and marijuana affect IOP

A

Lowers it

46
Q

How does LSD affect IOP

A

Elevates it

47
Q

What do steroids do to IOP

A

Increase IOP

48
Q

What is the largest organ of the eye

A

Virtuous

49
Q

What is the vitreous

A

A highly transparent gel

It is located between the crystalline lens and the retina

50
Q

The vitreous transmits ___% of light

A

90

51
Q

What are the 3 zones of the vitreous

A

Outermost: vitreous Cortex
Center: Cloquets canal
Intermediate: inner to cortex and surrounds canal

52
Q

What is teh vitreoretinal interface

A

Where the vitreous is attached to the inner limiting membrane of the retina by anchoring fibrils and membrane limitans interna (MLI)

53
Q

Where is the vitreous base ?

A

At the ora serrata

54
Q

What is the vitreous base attached to

A

NPCE and the internal limiting membrane of peripheral retina

It the the strongest attachment

55
Q

Is the vitreous base attachment affected by age?

A

No

56
Q

What is Weigers Ligament

A

It is between the posterior surface of lens and the anterior face of vitreous

It is a firm attachment

57
Q

Is weigers ligament affected by age?

A

Yes, it declines after age 35

58
Q

What is peripapllary adhesion

A

It is around the edge of optic disc
It is a medium attachment
Declines with aging
Weiss’ ring

59
Q

What is the macular/peripheral attachment

A

Weak
Controversial
May have an attachment 3-5mm posterior to vitreous base. Attach to retinal blood vessels

60
Q

What is in high composition in the vitreous

A 
H2O (99%)
Collagen (T2)
HA (GAG)
Vitreal Cells (hyalocytes, fibroblasts)
Vitamin C
61
Q

What is the gel structure of vitreous due to

A

Arrangement of collagen fibrils suspended in network of HA

62
Q

What do hyalocytes do

A

Synthesize glycoproteins for the collagen fibrils

Synthesize HA

63
Q

What do fibroblasts do

A

Synthesize the collagen fibrils

64
Q

What are the functions of the vitreous

A

Support retina
Diffusion barrier
Metabolic buffer
Transparency

65
Q

What are the support functions of the vitreous

A
  • Prevents retinal detachment
  • reduce mechanical deformation
  • supports lens during trauma
  • decreases transmission of light at 300-350 nm
  • mechanical support
66
Q

What is posterior vitreous detachment (PVD)

A

10% of eyes have a strong vitreous retina attachment
Vitreous traction can cause retinal tears
Possibility of vitreous hemorrhage
High risk of rhegmatogenous retinal detachment

67
Q

What is macular edema due to

A

Vitreous-retinal traction
Increase in passive permeability
Decrease in active transport across Blood retinal barrier
Increase osmotic pressure

68
Q

What is the diffusion barrier of the vitreous

A

Slow diffusion across vitreous
Bulk flow is limited across vitreous
Prevents topically administered substance from reaching the retina
Prevents substances in blood stream from reaching vitreous center
No diffusion barrier for small molecules

69
Q

What is the metabolic buffer of the vitreous

A

Reservoir for ciliary body and retinal metabolism
Movement of water soluble substances into vitreous and their dilution
Reservoir of glucose and glycogen for retinal metabolism
Reservoir of potassium for retinal metabolism
Reservoir for Vitamin c

70
Q

What can full PVD or vitrectomy) cause

A

Nuclear sclerotic cataract (NSC)

Reduce neovasculariztion in retina
Neovascualr glaucoma

71
Q

What causes the transparency of the vitreous

A

Low [macromolecules]
Low [protein]
Specific collagen/HA configuration
Blood vitreous barrier

72
Q

What is synchisis scintillations

A

Rare
Not age related
2% to injury or inflammation
It is an accumulation of the cholesterol

73
Q

What is asteroid hyalosis

A

In people aged 60-65
Common in white people
No decrease in VA
It is an accumulation of calcium

74
Q

What is dry eye syndrome

A

A disorder of the tear film caused by tear deficiency or excessive tear evaporation that causes damage to the interpalpebral ocular surface and is associated with symptoms of ocular discomfort

75
Q

What is the function of the tear film

A

Provides a smooth refractive surface for clear vision

Maintains the health of corneal and conjunctival epithelia

Acts as the first line of defense against microbial infections

76
Q

What are the layers of the tear film

A

Lipid layer
Aqueous layer
Mucous layer

77
Q

What is the mucus layer of the tear film composed of

A 
Mucin*
Immunoglobulin
Urea
Salts
Glucose
Leukocytes
Cellular debris
Enzymes
78
Q

What is mucin

A

A high molecular weight glycoproteins that is heavily glycosylated

79
Q

What are the 2 types of mucins

A

Membrane associated

Secretory

80
Q

What is membrane associated mucins

A

A dense Barrie to pathogen penetrate, at the epithelia cell tear film interface

81
Q

What are secretary mucins

A

Act as cleaning crew, moving through the tear film and collecting debris that can be removed via the nasolacrimal duct during blinking

82
Q

What is the function of the mucus layer

A

Maintain water on the surface of the eye

Mucins also interact with tear lipids to lower surface tension thereby stabilizing the tear film

Provides lubrication for eyelid movement

Traps exploited surface cell, foreign particles and bacteria

83
Q

What are the sources of the mucus layer

A 
Goblet cells (cornea and conj)
Squamous cells (cornea and conj)
84
Q

What is the neural control of the mucus layer

A 
Sensory nerves
Parasympathetic nerves (increases)

Sympathetic

85
Q

What is the aqueous layer composed of

A 
Water
Electrolytes
Proteins
Peptide
Growth factors 
Vitamins
Hormones
86
Q

What are the electrolytes in the aqueous layer

A 
Na*
Cl*
K*
Ca*
Mg
HCO3
Phosphate
87
Q

What is the importance of Na and Cl in the aqueous layer

A

They are the main controllers to osmolarity of tear film

Osmolarity increases with dry eye

88
Q

What is the importance of K and Ca in the aqueous layer

A

Important for maintaining corneal epithelial health

89
Q

What are some proteins in the aqueous layer

A 
Albmin
Immunoglobulins (IgA)
Histamine
Lactoferin
Lysozyme
Interleukins
Antimicrobials
90
Q

What are the functions of the aqueous layer

A

Electrolytes act as a buffer to maintain constant pH and contribute to maintaining epithelial integrity of the ocular surface

Offers a strong defense system to protect against invading microorganisms through contained proteins

Peptide growth factor A acts via autocrine and paracrine mechanisms to regulate epithelial proliferation, motility and differentiation

91
Q

The buffering system of the eye allows the eye to tolerate ophthalmic solutions of what pH

A

3.5-10.5

92
Q

What happens to eye pH while we are sleeping

A

It decreases (due to aerobic respiration)

93
Q

What happens to pH in dry eye

A

It increases (due to osmolarity increases)

94
Q

What are the resources of the aqueous layer

A

Lacrimal glands* (reflex and emotional tearing)

Accessory lacrimal glands (maintenance tearing)

95
Q

What is the neural control of the aqueous layer

A

Main lacrimal glands: parasympathetic, sympathetic, sensory nerves

Accessory glands: parasympathetic

96
Q

What is the lipid layer of the tear film composed of

A

Meibomian oil

97
Q

What are the 2 phases of the lipid layer

A

Polar surfactant phase

Nonpolar phase

98
Q

What is the polar surfactant phase

A

It is primarily composed of phospholipids and glycolipids

Acts as a surfactant between the hydrophilic aqueous mucin layers and thick, nonpolar lipid layer

99
Q

What is the nonpolar phase

A

It is primarily composed of wac, cholesterol esters, and triglycerides

Provides the air-tear film interface and is responsible for retarding evaporation

100
Q

What is the function of the lipid layer

A

Major barrier to evaporation from ocular surface

Provides stability to tar film through interaction with aqueous-mucin phase

Provides a smooth optical surface for the cornea

Acts as a barrier against foreign particles

101
Q

What are the resources of the lipid layer

A

Meibomian glands

Assistance from Zeis and Moll glands

102
Q

What is the neural control of the lipid layer

A

Parasympathetic innervation

103
Q

How can you access the tear film

A 
Tear secretion
Tear film stability
Tear film osmolarity
Lipid layer evaluation
Ocular surface evaluation
104
Q

What is tear deficient dry eye

A

There is a disorder in the lacrimal gland function, resulting in either reduced aqueous tear production and tear flow, or a failure to transfer lacrimal fluid into the conjunctival sac

105
Q

What is the largest dry eye category

A

Tear deficient

106
Q

What is evaporative dry eye

A

Lacrimal gland function is normal and the volume is sufficient to cover the surface, but another tear film abnormality exists that leads to increased tear evaporation

107
Q

What can lead to evaporative dry eye

A

Hyperosmolarity

Meibomian gland disease

108
Q

What tests access tear secretion

A

Schirmer 1 and 2
Phenol red thread test
Meinscometry

109
Q

What tests look at tear film stability

A

TBUT
Ocular protection index
Videokeratography
Tear turnover

110
Q

What tests tear film osmolarity

A

Tear film osmolarity
Tear ferning
Tear evaporation

111
Q

What tests lipid evaluation

A

Interferometry

Meibometry

112
Q

What tests ocular surface evaluation

A

Fluorescein
Rosa bengal
Lissamine green

Ocular Physiology (8 decks)

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