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Ocular Phys Block 9 > Corneal Function > Flashcards

Corneal Function Flashcards

(69 cards)

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1
Q

Primary function of the cornea

A

Refract light

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2
Q

Factors affecting refraction in the cornea

A
  • curvature of anterior surface
  • change in RI from air to cornea (tear film)
  • corneal thickness
  • curvature of posterior surface
  • change in RI from cornea to aqueous
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3
Q

What is the 1st refractive surface

A

Actually the tear film

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4
Q

Total power of the eye

A

60D

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5
Q

Power of the cornea

A

40-48D

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6
Q

How much power of the eye does the cornea have

A

2/3-3/4

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7
Q

What kind of focusing ability does the cornea have

A

Fixed focus. Squinting can actually change the corneal focus though

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8
Q

What is the second primary function of the cornea

A

Transmit light

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9
Q

How does the cornea transmit light

A

Minimal scattering
Minimal distortion
Maximal transmission

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10
Q

Keys to maximize light transmission

A
  • smooth optical surface (tear film)
  • regularity of surface epithelial cells
  • absence of blood vessels
  • arrangement of correct spatial arrangement of collage fibrils in stroma
  • less than 1% light scatter (majority at epithelium and endothelium)
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11
Q

How much light scatter int he cornea

A

1%

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12
Q

How to protect your cornea for long term vision

A

Minimize risk of infection
Prevent damage to the retina
Avoid penetrating injury
Swift healing mechanism

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13
Q

What is one of the most sensitive tissues in the human body

A

Cornea

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14
Q

Innervation of cornea

A
  • 200-600x greater than skin
  • 20-40x greater than roots in teeth
  • ophthalmic division of trigeminal nerve (60-80 long ciliary nerves)
  • unmyleinaed nerve endings
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15
Q

What is the cornea sensitive to

A

Touch
Temp (cold)
Chmicals

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16
Q

What does touching thecornea cause

A

Involuntary lid closure

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17
Q

What is the CV of the cornea

A

Endothelial integrity can be evaluated by determining the coefficient of variation (CV) of cell size

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18
Q

What is a normal CV for cornea

A

0.25

25% variation in shape and size of endothelial cells

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19
Q

What is a normal hexagonality of endothelial cells

A

69%

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20
Q

What is a normal endothelial cell count

A

2000 cells/mm2

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21
Q

What happens to endothelial cells as some of them die

A

Others will enlarge and try to take up some of the space

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22
Q

Why do we need to know endothelial cell count before surgeries

A

To make sure we are not causing damage to endothelium. It does not regenerate

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23
Q

Stroma makes up ______ of the cornea

A

90%

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24
Q

This is important in maintains corneal transparency int he stroma

A

Regularity of size of collagen fibrils (300A) and the spacing (550A) between collagen fibrils

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25
What maintains the precise arrrangment of collagen fibrils in the cornea
The negatively charged molecules located around each collagen fibrils by their bonds with water molecules
26
Blood vessels and corneal transparency
Lack of blood and lymph vessels
27
What else is lacking in the cornea that helps with transparency
Lack of myelin sheaths
28
Tough layer of collagen and laminin that protects the underlying layers of the cornea
Bowmans layer
29
Layers of the cornea
``` Epithelial Bowmans Stroma Dua Descemet's Endothelium ```
30
This is acellular, 8-14 microns thick, and resistant to deformation, trauma, and foreign bodies (will scar)
Bowmans layer
31
Dua's layer of the cornea
A new 6th layer - 15 microns thick - anterior to descemets membrane
32
What is the most important function of Dua's layer
Withstands high pressures
33
How much of the cornea is water
80% ish
34
How does the epithelium maintain corneal hydration
Tight junctions
35
How does the stroma maintain corneal hydration
Anionic proteoglycans pull water in
36
How does the endothelium maintain corneal hydration
Slowly leaks fluids into cornea
37
Mechanism by which cornea remains hydrated (78% water content)
Corneal deturgescnence
38
What is corneal hydration dependent on
- barrier function of the epithelium and endothelium - the anionic characteristics of molecules within the stromal matrix that account for the tendency of the stroma to imbibe water - water and ion transport through the epithelial and endothelial cell membranes
39
What is the movement of water out of the cornea from the stroma through the endothelium and into the aqueous or through the epithelium into tears mediated by
Ion flow and osmotic gradients
40
As ions are exchanged in the cornea and the concentration is altered
Water passage follows, moving down its concentration gradient. Cl- extrusion and Na+ absorption are the major driving forces for water transport across the epithelium and endothelium
41
Would you be concerned if you saw corneal edema following cataract surgery 5 min post op
No Concerned 1-7 days after surgery if it is still present
42
Phthisis bulbi
No longer maintinaing integrity and low pressure. No longer useful. Could remove and replace with artificial eye
43
Small integral membrane porteins residing in the plasma membrane, some are water selective, others also transport glycerol
Aquaporins
44
What do aquaporins form in the cornea
Bidirectional osmotic water transport channels across the plasma membrane
45
What do aquaporins function as in the cornea
Not only as channels but have some role in cellular processes, particularly in cell migration
46
IOP and cornea clouding
High IOP on the order of 50mm Hg or higher can move excessive water into the corneal stroma from the AC and overwhelm the endothelial transport system
47
Corneal abrasion and corneal haziness
Causes a loss of the zonular occludens barrier results in a localized area of edema and haziness
48
How can epithelial edema affect VA
Decrease it when it separates cells causing surface irregularities; it is uncomfortable and can be painful
49
Extensive epithelial abrasion
Allow fluid entrance into the stroma Bandage CL to help protect
50
What is unique about the cornea
Avascular
51
Where does most oxygen to the cornea come from
The air
52
Where do nutrients come from to the cornea
Diffusion through tear film and active transport through aqueous
53
What does the cornea relie on for healing
Peptide growth factors
54
What is the fastest healing tissue in the body
Cornea
55
Corneal abrasions heal in
24-48 hours
56
Corneal epithelium can be completely replaced in
2 weeks
57
Do you get a lot of O2 when you sleep to the cornea
No
58
Recurrent corneal erosion
Will feel a burning sensation when they wake up
59
What part of the cornea consumes most of the oxygen
Endothelium and epithelium | -25-30x of that of the stroma
60
Glycogen storage in the cornea
Epithelium can store glycogen
61
Inflammatory or infective condition that compromises the integrity of the epithelium
Corneal ulcer
62
What part of the cornea is hydrophobic
Epithelium and endothelium (non-polar compounds)
63
What part of the cornea has a high water content
Stroma
64
What is the epithelium impermeable to
Ions
65
Removal of epithelium can facilitate what
Uptake of water soluble drugs
66
What can generally penetrate the cornea more easily
Lipid soluble materials
67
Some drugs getting to the AC
Require high Cxn to reach AC. Heard for Abs to get into AC. Have to do IV or oral in high Cxn
68
Loss of stability and structure in the cornea
Keratoconus Ectasia High or low pressire
69
Corneal transplants
2,3 or more layers removed. Best to maintain persons endothelium

Ocular Phys Block 9 (5 decks)

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