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Scott Ugh Flashcards

1
Q

List the general main concepts of the cornea

A
  • part of the fibrous tunic
  • transparent
  • tough
  • HIGHLY innervates
  • avascular
  • major refractive component of the eye
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2
Q

Does the sclera or the cornea have a steeper curvature?

A

The cornea has a steeper curvature

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3
Q

What is the external sclera sulcus?

A

-where the cornea and sclera meet

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4
Q

Where does the vascular supply stop before it gets to the cornea?

A

At the corneaoscleral limbus

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5
Q

What is the bulbar limbus?

A

Fascia Bulbi (tenon’s capsule) strongly adheres to episclera and conjunctiva

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6
Q

What is the conjunctival limbus?

A

Conjunctiva extends 1mm beyond corneoscleral limbus

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7
Q

What is the optical zone?

A

Central 4 mm

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8
Q

What is the overall power of the cornea?

A

+43D

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9
Q

What is the shape and dimensions of the anterior cornea?

A
  • oval

- longer in horizontal (12mm) than vertical (11mm)

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10
Q

What is the shape and dimensions of the posterior cornea?

A
  • sphere

- both 11.7mm

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11
Q

What is the index of refraction of the cornea?

A

1.376

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12
Q

What is with the rule astigmatism?

A

Steeper in the VERTICAL meridian

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13
Q

What is against the rule astigmatism?

A

Steeper in the HORIZONTAL meridian

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14
Q

What is oblique astigmatism?

A

Steeper curvature in oblique axis

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15
Q

What is lenticular astigmatism?

A

Unequal curvature in the lens

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16
Q

What is the thickness of the central cornea? Peripheral cornea?

A

Central is 0.52mm and peripheral is THICKER at 0.70mm

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17
Q

What would the thickness of the cornea do to the IOP readings?

A

Thicker cornea would result in overestimation and thinner would result in underestimation

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18
Q

What is the best way to determine true IOP? What is the result measured in?

A

Pachymetry

-microns!!! (0.52mm equals 520 microns)

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19
Q

How many layers does the anterior epithelium have?

A

4 layers!

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20
Q

How any layers does the posterior epithelium have?

A

1!

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21
Q

What layer makes up the bulk of the cornea?

A

The stroma

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22
Q

How thick is the tear film?

A

7 microns!

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23
Q

What is the rate of production of the tear film?

A

1.2 microliter per minute

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24
Q

What are the three layers of the tear film?

A
  • lipid layer
  • aqueous layer
  • mucous layer
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25
What is the lipid layer of the tear film secreted by? What is the purpose of the lipids layer?
- secreted by meibomian glands in the palpebrae and caruncle - prevents the aqueous layer from evaporating
26
What is the aqueous layer of the tear film secreted by?
Secreted by the lacrimal gland and accessory lacrimal glands
27
What is the mucous layer of the tear film secreted by and what is the purpose of the layer?
- secreted by goblet cells in the conjunctiva | - decreases surface tension and provides a smooth, wetable surface for the aqueous layer
28
What adjoins the mucous layer to the cornea?
Glycocalyx
29
Can dry eye always be treated with artificial tears?
Hell no. -sometimes you can have epiphora (excess watering of the eye) so if the lipid layer is messed up, you can produce tears, but they evaporate
30
How thick is the corneal epithelium? What epithelium is it continuous with?
- 50-60 microns thick | - continuous with bulbar conjunctival epithelium
31
What kind of epithelium is the cornea epithelium?
5-7 layers of non-keratinized, non secretory, stratified, squamous epithelium
32
What are the three layers of the corneal epithelium?
- apical layer - wing cell layer - basal cell layer
33
How many layers is the apical layer? What kind of cells? What kind of junction is between the lateral surfaces of the apical cells?
- 1-2 layers - flattened squamous cells - tight junctions link cells to form semipermeable membrane on cornea
34
How long does it take to replace the zona occludens?
1 hour. Regular turn over
35
How many layers is the wing cell layer? What shape are the wing cells? What links the cells together? How does their shape change as they move towards the surface?
- 2-3 layers thick centrally and 4-5 peripherally - posterior is concave, anterior is convex - linked by desmosomes and gap junctions for communication - they flatten as they move towards the surface to replace apical cells due to pressure from eyelids
36
How many layers is the basal cell layer? What kind of cells are they?
- 1 layer | - columnar cells
37
What are the only cells in the corneal epithelium that undergo mitotic division?
Basal cells
38
What are hemidesmosomes?
- they (and anchoring fibrils) are responsible for attaching epithelium to underlying stroma - holds basal cells to Bowman's layer
39
What do the microvilli and microplicae do?
- they are on the surface of the epithelium and pick up oxygen from the air that is evaporated by tears - maintains mucoid layer for adherence to the aqueous layer
40
Which layer of the epithelium has a group of free nerve endings?
Basal layer
41
What is a corneal abrasion? What should you do?
- scratch on the cornea - usually painful, but not severe - dont rub your eye, clean with water/saline - lubrication and antibiotic
42
What is used to asses the size and depth of a corneal abrasion?
- fluorescent dye | - the dye will only stain damaged cells
43
What are palisades of Vogt?
-folds on the corneoscleral limbus that increase surface area and are a common site for stem cells
44
Bowman's layer: how thick? What kind of cells? Does it get regenerated? Where does it end? What is the function?
- 8-12um thick - no cells! - does not get regenerated! If damaged, replaced by thickened epithelium - ends at limbus (not continuous with bulbar conjunctiva epithelium) - provides structural support
45
Which can be stripped from the stroma, Bowman's layer or Descemet's membrane?
- Bowman's cannot be stripped from stroma! It is continuous! | - Descemet's membrane can be stripped from stroma
46
Why is Bowman's layer not a basement membrane?
It is Periodic acid-Schiff negative! All basement membranes should have GAGs and stain positive
47
What makes up 90% of corneal thickness?
Stroma! (450-550um thick)
48
What is the stroma made up of?
- collagen - keratocytes - ground substance - GAGs
49
How is the collagen of the stroma organized?
- organized into lamellae (250 lamella at 2um thick) - collagen is evenly spaced at 1/2 wavelength for transparency property - adjacent lamellae layers lie at 90 degrees relative of each other.
50
What to the GAGs of the stroma do?
Pull aqueous humor into cornea
51
Where do the keratocytes lie in the stroma? What do they do?
- lie between lamellae - communicate with each other by gap junctions - maintain ground substance and collagen - activate inflammation
52
What layer is the focus of refractive surgery?
Stroma
53
What is keratoconus? Munson's sign?
- Keratoconus: thinning of the stroma and eye loses shape and develops cone like bulge - Munson's sign: angulation of the lower lid on down gaze (seen in advanced keratoconus)
54
A corneal user is damage to what part of the cornea?
Stroma/ collagen (not just epithelium)
55
Descemet's membrane is the basement membrane for what?
Endothelium
56
Descemet's membrane: how thick? Does it regenerate? Where does it terminate?
- Anterior banded zone is laid down before birth and does not thicken - posterior unbranded zone is laid down after birth and thickens throughout life - overall progresses 3-15um thickness - it DOES regenerate if damaged - terminates at Schwalbe's line
57
What is Wilson's disease?
-kayser Fleisher ring (copper deposits in descemet's membrane) indicates disease in liver
58
Corneal endothelium: how thick? How many layers? How many cells normally and how many are required for normal function? How are the cells shaped?
- 4-5um thick - 1 layer - normally 400,000-500,000 cells, 400-700 cells/mm2 are required for normal function - cells are flat and hexagonal
59
The corneal endothelium is joined by a leaky barrier called what?
Macula occludens
60
Loss of cells in the corneal endothelium cause what?
Change in size (polymegathism) and shape (pleiomorphism)
61
Describe the counteracting process of the pump leak system and what happens when there is no pump action.
- stroma GAGs pull in aqueous humor into the cornea and endothelium cells pump aqueous humor our of the cornea - if there is not pump action, stromal edema occurs
62
If the cornea is avascular, where does it get its nutrients from?
- Anterior cornea: Tear film - Posterior cornea: Aqueous humor - Peripheral cornea vasculature (at limbus)
63
Name the things that contribute to the peripheral cornea vasculature
- 7 anterior ciliary arteries - anterior and posterior conjunctival arteries - superficial pericorneal plexus (conj) - deep pericorneal plexus (episclera)
64
Are there lymphatics in the cornea?
Nope
65
Are there lymphatics in the conjunctiva?
-yes! Lateral goes to preauricular lymph nodes and medial goes to submandibular lymph nodes
66
How sensitive is the cornea?
300-600 times more sensitive than Michael Jordan crying
67
How nerves are responsible for sensory innervation of the cornea?
Long posterior ciliary nerves
68
What do the posterior long ciliary nerves run through to make a plexus in corneoscleral limbus region?
Supra choroidal space
69
What is the name of the plexus that innervates middle and anterior stroma?
Subepithelial plexus
70
What is the name of the plexus that passes through Bowman's layer to enter the epithelium? Are they myelinated?
-intraepithelial plexus. Not myelinated
71
What parts of the cornea have sensory innervation?
- middle/anterior stroma - epithelium -NOT POSTERIOR STROMA, DESCEMET'S MEMBRANE, ENDOTHELIUM
72
Describe Photorefractive keratectomy
- corneal epithelium is derided with tool - laser hits anterior stroma - bandage contact - re epithelization of cornea - PAINFUL
73
Describe LASIK
- flap in epithelium - ablate anterior stroma - put flap back - can develop a scar
74
Describe radial keratotomy
-radial incisions cut into stroma to flatten the cornea
75
What would help you correct irregular astigmatism?
Penetrating keratoplasty
76
What are scleral contact lenses?
-large diameter RGP that vaults the cornea and rests on the bulbar conjunctiva and underlying sclera
77
What patients can benefit from scleral CLs?
- irregular astigmatism - keratoconus - dry eye - high refractive error
78
What should you use as the liquid reservoir for scleral CL?
-non preserved-saline solution NaCl
79
The tear reservoir with scleral contact lenses must cover what?
- cornea from apex of the cornea to the limbus! | - make sure the height/vault is correct to make sure tear reservoir adequately covers the entire cornea

Ocular 6 (6 decks)

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