Cornea

Question 1

what is included in the outermost fibrous tunic of the eye

Answer 1

the transparent cornea and the opaque sclera

Question 2

how much of the eyeball does the cornea contribute

Answer 2

1/6th

Question 3

what is the corneoscleral limbus

Answer 3

the area of the merging of the cornea and the sclera

Question 4

how much refractive power does the cornea contribute

Answer 4

(43.1 to 48.8D) 3/4

Question 5

how thick is the central and peripheral part of the cornea

Answer 5

the center is about 0.52mm and increases to 0.70mm

Question 6

how big is the optical zone

Answer 6

the central 1/3 of the cornea or 4mm

Question 7

what are the 5 layers of the cornea

Answer 7

epithelium, bowman’s layer, stroma, descemets membrane, endothelium

Question 8

what cells make up the corneal epithelium

Answer 8

stratified nonkeratinized, nonsecretory, squamous epithelium

Question 9

is the corneal epithelium regularly or irregularly arranged

Answer 9

regular to permit light to enter

Question 10

what cells are absent in the center of the corneal epithelium that are present in the periphery

Answer 10

melanocytes and immunocompetent dendritic cells

Question 11

what is the most superficial layer of the corneal epithelium

Answer 11

the apical layer

Question 12

what does the apical layer of the epithelium secrete

Answer 12

glycocalyx- also has microvilli and ridges to increase the surface area to stabilize the tear film

Question 13

how are the apical cells joined together

Answer 13

tight junctions along the lateral walls to prevent passage of fluid between the cells and excessive uptake of fluid from the tear film

Question 14

what layer is directly below the apical layer

Answer 14

wing cell layer

Question 15

how do the wing layer connected

Answer 15

via desmosomes and communicate gap junctions

Question 16

what shape are wing cells

Answer 16

polyhedral , anterior surface is convex/posterior concave to fit over the basal cells

Question 17

what is the basal cell layer (basement membrane) made of

Answer 17

columnar cells, stand in perfect alignment

Question 18

how do the basal cells attach to the basement membrane (basal lamina)

Answer 18

hemidesomosomes, communicate with gap junctions

Question 19

how is the basement membrane formed for the basal cell layer of the epithelim

Answer 19

secreted by the basal cells, anchored by fibrils pass through the basement membrane and bowmans layer

Question 20

how are the basal cells and the wing cells connected

Answer 20

via desmosomes

Question 21

when the basal cells are migrating toward the center of the cornea, where do they originate from peripherally

Answer 21

the Palisades of Vogt

Question 22

what are the Palisades of Vogt

Answer 22

located in the radial folds of the epithelium of the limbus, may harbor stem cells

Question 23

which layer of the corneal epithelium undergoes mitotic division

Answer 23

the basal cells

Question 24

what is the second layer of the cornea

Answer 24

bowman’s layer

Question 25

why is bowman's layer not a membrane

Answer 25

It is PAS -

Question 26

can bowman's layer regenerate?

Answer 26

No, it is produced pre-natally, lacks keratocytes (fibroblast) cells

Question 27

what replaces bowman's layer if it is damaged

Answer 27

the epithelium thickens in its place

Question 28

which layer of the cornea is the thickest, about 90%

Answer 28

the stroma (substantia propria)

Question 29

what is the stroma made of

Answer 29

an extracellular matrix of arranged collagen fibers

Question 30

how far apart must the collagen fibrils be to keep the cornea transparent

Answer 30

must be less than one half the wavelength of visible light (400-700nm)

Question 31

where is descemet's membrane

Answer 31

lies on the posterior surface of the stroma (substantia propria) serving as a basement membrane for the corneal endothelium

Question 32

which layer of the cornea thickens from birth to adult

Answer 32

Descemet's membrane

Question 33

can descemet's membrane be reformed if damaged

Answer 33

yes

Question 34

what is Schwalbe's line

Answer 34

the anterior border ring of the trabecular meshwork- where Descemet's membrane abruptly stops at the corneal margin

Question 35

what are Hassall-Henle Bodies

Answer 35

small transparent growths, that increase with age, on the posterior surface of Descemet's membrane at the periphery of the cornea, they protrude the anterior chamber

Question 36

what is corneal guttata

Answer 36

when Hassall-Henle Bodies occur in the central cornea instead of the periphery

Question 37

what is the corneal endothelium comprised of

Answer 37

single layer of flat, hexagonal arranged cells, uniform size, with the apical end facing the anterior chamber and basal ends apposed to Descemet's membrane

Question 38

what type of barrier does the corneal endothelium provide

Answer 38

a leaky barrier allowing nutrients from the aqueous humor to enter the avascular stroma

Question 39

what junctions are connecting the corneal endothelium cells

Answer 39

macula occludens, dont completely encircle the cells to allow a leaky barrier

Question 40

what is the corneoscleral limbus

Answer 40

junction of the cornea and the sclera, encircles the peripheral cornea, external scleral sulcus is here

Question 41

where are the trabecular meshwork and canal of schlemm located

Answer 41

in the internal scleral sulcus

Question 42

at the corneal periphery, which structures are continuous with others

Answer 42

corneal epithelium- conjunctival epithelium, corneal stroma- scleral stroma, corneal endothelium- endothelial cells of trabecular meshwork

Question 43

which layers terminate at the corneal periphery

Answer 43

Bowmans layer and Descemet's membrane

Question 44

what is the sensory innervation to the cornea

Answer 44

long ciliary nerves from the ophthalmic division of the trigeminal nerve

Question 45

where do the long ciliary nerves travel to reach the cornea

Answer 45

through the perichoroidal space between the sclera and the choroid

Question 46

which layers of the cornea do not have innervation

Answer 46

Descemet's layer and corneal endothelium