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Cornea Flashcards

1
Q

What 2 corneal measurements increase with age in adult dogs?

A

Corneal thickness

Descemet’s thickness

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2
Q

What are the 3 predominant GAGs in the cornea?

A

Keratin sulfate
Dermatin sulfate
Chondroitin sulfate

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3
Q

What is the normal cell density of endothelial cells?

A

2500-3100 cells/mm2

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4
Q

What is the average thickness of the canine cornea?

A

~560 um (pachymetry)

~85 um (confocal microscopy)

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5
Q

What nerve innervates the cornea?

A

Trigeminal

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6
Q

Who has a decr density of nerves in the cornea?

A

Brachycephalics

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7
Q

What part of the cornea is the most sensitive?

A

Central

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8
Q

Other than brachycephalics, what other group has decr corneal sensitivity?

A

Diabetics

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9
Q

What has more sensitivity: dorsal/ventral cornea, or nasal/temporal cornea?

A

Nasal/temporal

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10
Q

Does morphine 1% affect epithelialization?

A

No

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11
Q

What is the average turnover of corneal epithelium?

A

2 wks

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12
Q

What is the term for when epithelial cells move over a defect?

A

Epithelial sliding

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13
Q

What is the lag time between injury and start of epithelial sliding?

A

1 hr

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14
Q

If the entire corneal epithelium is removed, most species can cover it by sliding CONJUNCTIVAL epithelium in how much time?

A

48-72 hrs

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15
Q

Epithelial spreading results in a thin epithelial barrier. How do epithelial cells increase the thickness?

A

Mitosis

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16
Q

PMNs enter the cornea from what TWO sites?

A

Tear film and conjunctival vessels

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17
Q

What cells in the corneal stroma transform after injury? What do they transform into?

A

Keratocytes –> fibroblasts

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18
Q

Name the 6 phases of corneal wound healing?

A
  1. Immediate
  2. Leukocytic
  3. Epithelial
  4. Fibroblastic
  5. Endothelial
  6. Changes in organization and cellularity
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19
Q

Describe what happens in the immediate step of corneal wound healing?

A
  1. Outer stromal fibers and Descemet’s retract, causing gaping on either side of the wound
  2. Fibrinogen (from inflamed AH) come into contact with wound
  3. Fibrinogen is transformed into fibrin, and forms a plug
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20
Q

In a perforation, name the 4 ways PMNs can get to the wound (for the leukocytic phase)?

A

Tear film
Conj blood vessels
AH
Perilimbal vessels (if chronic)

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21
Q

How long does it take PMNs to reach the wound?

A

0.5-5 hrs

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22
Q

How long does it take mononuclear cells to reach the wound?

A

12-24 hrs

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23
Q

What 2 things monocytes do in the wound?

A

Scavenge

Transform into fibroblasts

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24
Q

Why is the epithelial phase so important to wound healing?

A

It is needed for transformation of keratocytes and mononuclear cells to fibroblasts

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25
Q

What happens if epithelium does not cover the wound?

A

Wound healing is significantly delayed

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26
Q

How long does the fibroblastic phase take to start?

A

12 hrs

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27
Q

Which keratocytes are transformed first?

A

Those closest to the wound edge

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28
Q

When does the endothelial phase begin (time)?

A

24 hrs

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29
Q

What occurs in the endothelial phase of wound healing?

A

Endothelial sliding or amitotic multiplication

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30
Q

What change to Descemet’s would indicate an old corneal perforation (histologically)?

A

Descemet’s duplication

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31
Q

How long does it take for corneal incisions to heal for significant strength to allow suture removal?

A

19 days

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32
Q

What 3 organisms make a ton of exogenous proteases?

A

Fusarium, Aspergillus, Pseudomonas

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33
Q

What 2 MMPs are especially important in corneal remodeling and degradation?

A

MMP-2 and -9

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34
Q

Where is pigment usually deposited in the cornea?

A

Basal epithelial cells

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35
Q

In the rabbit, 24 hrs after removal of the endothelium vs epithelium increased corneal thickness by?

A

Endothelium: 500%
Epithelium: 200%

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36
Q

Where is most of corneal edema distributed in the cornea?

A

Posterior lamellae

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37
Q

Uveitis results in cornea edema due to what 2 changes?

A
  1. Increased endothelial permeability

2. Decr function of Na-K ATPase pump

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38
Q

What virus causes blue eye?

A

Infectious canine hepatitis (canine adenovirus)

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39
Q

What type of reaction occurs with infection of infectious canine hepatitis?

A

Type III hypersensitivity

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40
Q

Why is blue eye seen with infection of CAV?

A

Immune complex formation after release of virus from infected endothelial cells

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41
Q

What breed is predisposed to blue eye?

A

Afghan hound

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42
Q

What vaccine is more likely to cause blue eye?

A

CAV-1 modified live

43
Q

What vaccine is less likely to cause blue eye?

A

CAV-2

44
Q

Of those dogs that develop blue eye (from vaccination or natural infection), what percentage will have permanent corneal edema?

A

30%

45
Q

Intraocular irrigation can increase risk of corneal endothelium damage if volume is over how many mL?

A

100 mL

46
Q

Intraocular irrigation can increase risk of corneal endothelium damage if time is over how many minutes?

A

20 min

47
Q

Where do superficial vessels originate from?

A

Conjunctiva

48
Q

Where do deep vessels USUALLY originate from?

A

Anterior ciliary bidy

49
Q

Where do deeps vessels RARELY originate from, and when does this happen?

A

Iris; if anterior synechiae

50
Q

Is corneal depth consistent with vessel growth?

A

YES–they grow along a lamellar plane

51
Q

Microcornea size?

A

<12 mm

52
Q

3 diseases associated with microcornea

A
  1. Merle ocular dysgenesis
  2. Multiple ocular anomalies
  3. Ehlers-Dalos syndrome
53
Q

Megalocornea size?

A

> 16-18 mm

54
Q

What disease commonly occurs with megalocornea?

A

Congenital glaucoma and buphthalmos

55
Q

What part of the cornea is a dermoid most commonly seen?

A

Temporal limbus

56
Q

What part of the cornea is a dermoid RARELY seen?

A

Central cornea

57
Q

Are dermoids usually superficial or deep?

A

Usually superficial

58
Q

What is the max number of superficial keratectomies that can be performed at one site?

A

2-3

59
Q

Why is there a limit to the number of superficial keratectomies that can be performed?

A

Stroma doesn’t usually regenerate completely

60
Q

Why is the carbon argon laser not appropriate for cornea surgery?

A

Generates heat = coagulates tissue = too much damage

61
Q

What type of laser can be used for corneal surgery?

A

Argon-fluoride excimer laser

62
Q

What are the 3 descriptive terms used for a corneal opacity (by density)?

A

Nebula, Macula, Leukoma

63
Q

How does a nebula appear?

A

Minor, diffuse, hazy, indistinct borders

64
Q

How does a macula appear?

A

Moderately dense, with CIRCUMSCRIBED borders

65
Q

How does a leukoma appear?

A

Dense and white

66
Q

If iris is at the back of a leukoma, what is the proper descriptive term?

A

Adherent leukoma

67
Q

What part of the cornea (specifically) is puppy dystrophy seen?

A

Subepithelial

68
Q

Is puppy dystrophy congenital?

A

No

69
Q

When is puppy dystrophy seen (age)? When does it disappear?

A

Usually <10 wks, but def gone by 12-16 wks

70
Q

What corneal opacity can be associated with a PPM?

A

Adherent leukoma

71
Q

What causes a PPM?

A

Embryonic vasculature structures fail to completely regress

72
Q

Specifically, where is the corneal opacity seen with Peter’s anomaly?

A

Paracentral

73
Q

Why is a corneal opacity seen with Peter’s anomaly (what structures are involved)?

A

Damage to endothelium and Descemet’s

74
Q

How common are colobomas or staphylomas in the dog?

A

RARE

75
Q

Why do staphylomas appear black?

A

Uveal tissue is showing

76
Q

What other abnormality is commonly seen with staphylomas?

A

Strabismus

77
Q

What are 6 causes of staphylomas?

A
  1. Congenital
  2. Inflammation
  3. Glaucoma
  4. Trauma
  5. Neoplasia
  6. Surgery
78
Q

What breed specifically has an increased prevalence to staphylomas?

A

Miniature doxies

79
Q

What is histologically characteristic of a SCCED?

A

Superficial stromal acellular hyalinized zone

80
Q

Avg age for a SCCED?

A

8-9 yrs

81
Q

Where on the cornea do SCCEDs usually occur?

A

Axial or paraxially

82
Q

How can you differentiate bullous keratopathy and secondary ulcer vs a SCCED with edema?

A

Edema in a SCCED is MILD and confined to affected area

83
Q

How does SCCED vascularization differ if the lesion is axially vs peripheral?

A 
Axial = can be present for MONTHS without vascularization
Peripheral = more likely to vascularize
84
Q

How deep can a diamond burr make a defect?

A

Into epithelial basement membrane but NOT beyond

85
Q

When is tissue adhesive NOT recommended for ulcers?

A

If deep/descemetocele = ocular toxicity

86
Q

What is the biggest downside to a tarsoconjunctival graft?

A

Eyelids are mobile = TENSION

87
Q

Why should epithelium be debrided prior to graft placement? (2)

A
  1. Graft can’t adhere if epithelium is there

2. Epithelial down growth can lead to graft dehiscence

88
Q

How thick is D’s membrane?

A

3-12 uM

89
Q

At what time point (hours) after prolapse should the prolapsed iris be amputated?

A

If incarcerated >6-8 hrs

90
Q

How do you remove prolapsed iris?

A

Pull slightly to get fresh uveal tissue, and cauterize newr the cornea

91
Q

3 most common bacteria that infect the cornea?

A
  1. Strep
  2. Staph
  3. P. aeruginosa
92
Q

What virus can cause ulcerative lesions in dogs?

A

CHV-1

93
Q

CHV-1 ulcers in dogs– what depth are they?

A

Superficial = NO stromal loss

94
Q

How can you diagnose CHV-1 keratitis definitely in dogs?

A

Virus detection (vs FHV in cats… CHV-1 is NOT ubiquitous so positive test supports diagnosis)

95
Q

What burn is usually WORSE: ACID or ALKALI?

A

Alkali

96
Q

What do acids do the the cornea? How does this affect prognosis?

A

They tend to cause protein coagulation in EPITHELIUM = limits penetration/depth = SUPERFICIAL and NON-PROGRESSIVE

97
Q

What do alkali do to the cornea? (3)

A
  1. They a LIPOPHILIC = cause SAPONIFICATION of fatty acids of cell membranes = cell death
  2. Hydrolyze intracellular GAGs and denature collagen
  3. Above damage stimulates inflammation and poteoytic enzymes
98
Q

Treatment for chemical burns?

A
  1. IRRIGATE for 10-15 min or until ocular pH is normal
  2. Treat with anati-collagenases
  3. Treat as you would an ulcer = ABx, mydriatics, systemic NSAID or steroid
  4. If needed, conj graft
99
Q

Irrigation for chemical burn– where should you be sure to irrigate?

A

Under the TEL

100
Q

What are 4 sources of proteases/collagenases?

A
  1. Infectious organisms
  2. PMNs
  3. Fibroblasts
  4. Epithelial cells
101
Q

What breed(s) are prone to rapidly progressive corneal pigmentation?

A

Brachycephalic– esp Pug, Shih Tzu, Pek, Lhasa

102
Q

Where does pigmentary keratitis usually start?

A

Nasally

103
Q

Where do melanocytes originate from to produce pigmentary keratitis?

A

Perilimbal

104
Q

Possible treatments for pigmentary keratitis?(4)

A
  1. Keratectomy– but scarring and recurrence!
  2. Strontium-90 plesiotherapy
  3. Cryotherapy
  4. Topical: CsA, tacro, steroids

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