Lecture 1 1/28/25

Question 1

What are the three layers of the cornea?

Answer 1

-epithelium
-stroma
-endothelium with descemet’s membrane

Question 2

How thick is the cornea in different species?

Answer 2

-1/2 mm thick in dogs and cats
1 mm thick in horses

Question 3

What is the limbus?

Answer 3

area between the cornea and the sclera/conjunctiva

Question 4

How is the corneal epithelium attached to its basement membrane?

Answer 4

via hemidesmosomes

Question 5

What are the characteristics of the corneal stroma?

Answer 5

-contains keratinocytes that make new collagen
-has fibers that stretch all the way across the cornea to maintain transparency
-makes up 90% of corneal thickness

Question 6

What are the characteristics of the corneal endothelium?

Answer 6

-pumps excess fluid out of the cornea
-single cell layer

Question 7

What are the characteristics of corneal innervation?

Answer 7

-via ophthalmic division of trigeminal nerve
-most sensitive tissue in body
-superficial injury is more painful than deep
-sensory innervation supplies factors necessary for corneal health

Question 8

Why are superficial eye injuries more painful than deep injuries?

Answer 8

-nerve ending are just under the epithelium
-deep lesions destroy the nerves, causing less pain

Question 9

Why do brachycephalic breeds have less of a response to eye injuries compared to other breeds?

Answer 9

brachycephalic breeds have less nerve concentration in the eye compared to other breeds

Question 10

What are the functions of the cornea?

Answer 10

-support intraocular contents
-transmit light
-refract light

Question 11

How does the cornea receive nutrients?

Answer 11

-aqueous humor delivers glucose, amino acids, vitamins, and other nutrients
-tears and palpebral conjunctiva supply oxygen (mainly tears)

Question 12

What are the mechanisms that allow the cornea to maintain clarity?

Answer 12

-avascularity
-no pigment
-non-keratinized epithelium
-highly organized collagen fibril arrangement
-relative dehydration
-tear film

Question 13

What are the ways in which the cornea responds to disease?

Answer 13

-edema
-cellular infiltration
-scar formation
-pigmentation
-vascularization
-keratinization
-secondary uveitis

Question 14

What is corneal edema?

Answer 14

influx of fluid into the stroma as a result of endothelial damage and/or loss of epithelium

Question 15

Which conditions can cause corneal edema?

Answer 15

-glaucoma
-ulceration
-uveitis
-endothelial dystrophy
-lens luxation

Question 16

What can lead to WBC infiltration of the cornea?

Answer 16

-infected corneal ulcers
-immune-mediated disease
-neoplasia

Question 17

What leads to scar formation/fibrosis?

Answer 17

abnormal arrangement of collagen fibers

Question 18

What are the characteristics of corneal pigmentation?

Answer 18

-indicates chronic disease
-causative disease can be active or inactive
-rarely goes away 100% after resolving underlying cause

Question 19

What are the characteristics of corneal vascularization?

Answer 19

-indicates active chronic disease
-takes 7-10 days for vessels to start growing to a visible point
-grow 1-2 mm per day

Question 20

What are ghost vessels?

Answer 20

vessel tracks that remain in the eye without blood after the disease that caused vascularization resolves

Question 21

What are the characteristics of keratinization?

Answer 21

-normally non-keratinized epithelium becomes keratinized
-seen with dry eye
-can be reversed

Question 22

What are the characteristics of secondary uveitis?

Answer 22

-inflammation inside of eyeball
-results from axonal nerve reflex

Question 23

What are the two methods of stromal defect healing?

Answer 23

-avascular: scarring with no blood vessels; collagen reforms after 6-12 months
-vascular: greatest amount of scarring; blood vessels visible

Question 24

What are the three layers of the corneal epithelium?

Answer 24

-basal cells
-wing cells
-squamous cells

Question 25

What are the characteristics of the epithelial basal cells?

Answer 25

-deepest layer -single cell thickness -layer that attaches to basement membrane via hemidesmosomes -only epithelial layer to undergo mitosis

Question 26

What is the epithelial wing cell layer?

Answer 26

middle transitional layer between the basal cells and squamous cells

Question 27

What are the characteristics of the epithelial squamous cells?

Answer 27

-anterior layer -contains microplicae and microvilli on surface to stabilize tear film -tight junctions between cells limits permeability

Question 28

What are the steps of healing for epithelial defects?

Answer 28

-corneal epithelial cells sense a loss of "contact inhibition" -basal epithelial cells slide across bare corneal stroma -fibronectin is laid down on stromal surface -fibronectin receptors on basal epithelial cells attach to fibronectin and "ratchet" across the stroma using actin and myosin -epithelial cells undergo mitosis to thicken new layer once covering the stroma

Question 29

What are the steps of avascular healing for stromal defects?

Answer 29

-neutrophils enter via chemotaxis -local keratocytes die -surrounding keratocytes transform into fibrocytes that migrate and synthesize collagen and mucopolysaccharide -matrix metalloproteinase enzymes produced by the cornea and PMNs degrade necrotic tissue -epithelium migrates to cover the defect

Question 30

What are the steps of vascular healing for stromal defects?

Answer 30

-cells infiltrate the defect at a greater rate than in avascular healing -vessels invade the stroma -granulation tissue is created -vessels collapse and become ghost vessels