Cornea and Sclera

Question 1

why is the sclera opaque

Answer 1

irregular array of collagen fibers and water content

Question 2

the sclera is avascular except for the…

Answer 2

superficial vessels of the episclear and intrascleral vascular plexus

Question 3

what type of collagen is the sclera 90% of

Answer 3

type 1

Question 4

which collagen is expansible tissue.
which is control of fibril dimension.
which is the ability to resist tension

Answer 4

type 3
type 5
type 1

Question 5

the large change in the refractive index of the cornea compared to air and by the corneal curvature produes the……

Answer 5

refracting element

Question 6

which is the most prominent interface w/in the cornea

Answer 6

the interface btwn the basal cells and the basement membrane

Question 7

which wavelenths are absored more in the cornea

Answer 7

shorter

Question 8

in wound healing, the goal is to promote_______ and not ______ by controlling fibroblast activatoin

Answer 8

regeneration

fibrosis

Question 9

to maintain cell regularity in corneal epithelial transparency, the cornea must prevent _______ from acculmualting and causing________ of cells and fibers

Answer 9

prevent water from accumulating and causing swelling/disorganization of cells and fibers

Question 10

the cornea contains large concentrations of glycosaminoglycans which created an environment with a ______

Answer 10

high osmotic pressure

Question 11

what maintain a barrier to fluid and ion transport in the cornea

Answer 11

tight junctions

Question 12

what tight junction protein is at the site of the suprabasal epithelium

Answer 12

claudin

Question 13

what is the basment membrane adhered to the basal cells by

Answer 13

hemidesmosomes and trans-plasma membrane collagen

Question 14

the corneal epithelium has relatively low ________ through its _______cell membrane

Answer 14

ionoic conductance

apical

Question 15

the movement of sodium from the tears into the epithelium is by ______ but ______is required to move it into the stroma

Answer 15

diffusion

active transport

Question 16

what is ion transport into the cornea mediated by

Answer 16

NA/K ATPase and CA/Mg ATPase

Question 17

what is the inward flux of sodium from the tears balnced out by

Answer 17

the outward movment of chloride into the tears

Question 18

What is the driving force for the transport of chloride into the tears

Answer 18

the movemnt of sodium into the stroma by the pump

Question 19

what pump in the basolateral membrane maintains the sodium gradient for the NaCl co-transport

Answer 19

Na/K pump

Question 20

how does chloride move into the cell against an electrochemical gradient

Answer 20

the Na-K-Cl co-transport

Question 21

stimulation of the beta adrenergic receptors and serotonergic receptors increases ……

Answer 21

apical chloride conductance

Question 22

the K channel is under _____ via _____ mediated pathway

Answer 22

parasympatheic control

cGMP

Question 23

what channel is mechano-senstivie

Answer 23

K channel

Question 24

what causes an increase in current through the K channels as the cornea swells

Answer 24

hyposmotic solutions

Question 25

what channel acts as a regulatory channel controlling osmolarity and cell volume

Answer 25

K channel

Question 26

the K channel is sensitive to ___ changes

Answer 26

pH

Question 27

what is intracellular pH regulated by

Answer 27

lactate-H co tranport and Na H exchange

Question 28

epithelial transport of water is ____ compared to endothelial pump

Answer 28

HELLA SMALL

Question 29

what is the water transporter that is important for the maintenance of normal corneal stromal thickness

Answer 29

aquaporin 5

Question 30

what kind of innervation do the chloride channels do?

Answer 30

sympatheitc innervation

Question 31

what kind of innervation do the potassium channels do?

Answer 31

parasympatheic innervation

Question 32

where do the new basal cells originate from

Answer 32

stem cells at limbus

Question 33

what is maintained by the shedding of superficial cells and proliferation of cells

Answer 33

epithelium

Question 34

there is no cell ______ in surface epithelial cells or wing cells

Answer 34

division

Question 35

wehre do the basal cells migrate towards

Answer 35

center of cornea (123 mM per week)

Question 36

how much basal cell division occurs per day

Answer 36

10-15%

Question 37

when do hemidesmosomes form during in a invasion-abrasion response

Answer 37

early period (18 hours)

Question 38

the release of epidermal growth factor (EGF) initiates the production of fibronectin to cover the damaged area when what is damaged

Answer 38

basement membrane

Question 39

what serves as a temporary matrix for cell adhesions

Answer 39

fibronectin

Question 40

in the stroma, which collage is the one that regulates fibril thickness? which collagen is < 5nm in diameter?

Answer 40

type 5 | type 1

Question 41

which types of collagen are found in the normal basement membrane

Answer 41

4 and 7

Question 42

why does the stroma need type 1 collagen filaments to be < 5 nm

Answer 42

corneal transparency. narrow diameter fibers dont cause light to scatter

Question 43

type 1 collagen fibers make up ____% of collagen fibers in the stroma

Answer 43

50-55%

Question 44

in addidtion to types 4 and 7, what other unique collagen types are found in bowmans and descemets membrane

Answer 44

5, 8, 11, 12

Question 45

in size theory of transparency, the fibril size is _____ and interfibril distance is less than ______

Answer 45

<30 nm | less than half the wavelenth of light

Question 46

light scattered by fibrils of uniform diameter is cancelled by ______

Answer 46

destructive interference

Question 47

do collagen fibrils have to be of equal diameter and equidistant from each other?

Answer 47

NOPE

Question 48

what is the principle that says when a wave passes through an opening the waves nearest the opening margins are slowed and the wavefront becomes curved

Answer 48

huygen's-fresnel principle

Question 49

waht maintins the regular spacing and packing of the collagen fibrils

Answer 49

proteoglycans

Question 50

what do corneal GAGs exist in the native state as

Answer 50

proteoglycans

Question 51

how does the cornea maintain fibril spacing

Answer 51

GAGs connect their next nearest neighbor collagen fibrils and form a ring like structure around each fibril

Question 52

what is involved in regulating collagen fiber diameter

Answer 52

keratan sulphate

Question 53

what is involved in regulating interfibrillar spacing

Answer 53

dermatan sulphate

Question 54

collagen abnormalities and its relationship to proteoglycans can result in the loss of...

Answer 54

transparency

Question 55

what is does abnormal keratan sulphate synthesis result in

Answer 55

macular dystrophy

Question 56

what % is the cornea hydrated? | what % is the sclera hydrated

Answer 56

80% | 70%

Question 57

why will the cornea absorb more water if it is placed in saline

Answer 57

bc of the high concentration of GAGs

Question 58

what does the swelling pressure produce?

Answer 58

inter-fibril tension that helps to maintain regular arrangemnt of fibrils

Question 59

what is swelling pressure related to

Answer 59

thickness

Question 60

what is the name for specialized fibroblasts residing in the stroma

Answer 60

corneal keratocytes (fibroblasts)

Question 61

what are speciliized fibroblasts found in the stroma important in (3 things)

Answer 61

1. maintaining transparency 2 wound healing 3. synthesizing matrix components

Question 62

keratocytes remain _____ until required

Answer 62

dormant

Question 63

what do keratocytes express

Answer 63

corneal crystallins

Question 64

what are responsible for the production and maintenance of the extracellular matrix of the stroma

Answer 64

keratocytes

Question 65

tensile strength of keratocytes increases up to the ....

Answer 65

fourth postoperative year

Question 66

______ incisions heal more slowly than _____ incisions

Answer 66

central | peripheral

Question 67

____ is a form of controlled cell death w/o the release of lysosomal enzymes or other intracellular components that could damage surrounding tissue

Answer 67

keratocyte apoptosis

Question 68

when do the dying stromal cells undergo necrosis

Answer 68

after the initial wave of apoptosis

Question 69

are metabolic processes temperature dependent

Answer 69

duh

Question 70

the metabolic pump moves what?

Answer 70

ions NOT WATER

Question 71

what balance does transparency depend on

Answer 71

leak/ion pump balance

Question 72

why do cells enlarge w/ aging

Answer 72

w/ the loss of cells, cells from surrounding areas spread to fill the space

Question 73

when are the pump and barrir restored in endothelial wound healing

Answer 73

when the single layer is restored

Question 74

which pump sites are increased w/ endothelial wound healing

Answer 74

Na K ATPase

Question 75

where is oxygen obtained from

Answer 75

tears, small amonts from aqueous and limbal vasculatoure

Question 76

glucose, amino acids, and vitamins are obtained from...

Answer 76

aqueous

Question 77

the inflammatory response in contact lens inhibits the....

Answer 77

Na/K ATPase

Question 78

what can contribute to epithelial thinning associted w/ long term contact lens use

Answer 78

decreased mitosis rates

Question 79

reduction in ______ is thought to be the result of prolonged epithelial edema in long term CL use

Answer 79

desmosomes | intercellular hemi-desmosomes

Question 80

what causes keratinization of the ocular surface epithelium

Answer 80

vit a deficiency

Question 81

the ionic barrier in the corneal epithelium generates a transepithelial potential of _________

Answer 81

25 - 35 mV

Question 82

what is the xyz hypothesis of cell maintenance of epithelial wound healing

Answer 82

``` X = proliferation of basal cells Y = Centripetal movement of cells Z = Cell loss from the surface ```

Question 83

How long would it take for a 6mm corneal would to heal?

Answer 83

48 hours

Question 84

How many different types of collagen have been detected in the eye?

Answer 84

22

Question 85

light scatter only occurs when the distance between two regions of different refractive index become greater than ______

Answer 85

200 nm

Question 86

The stroma represents about _______ % of corneal thickness

Answer 86

85 - 90%