Lecture 1 1/28/25 Flashcards
What are the three layers of the cornea?
-epithelium
-stroma
-endothelium with descemet’s membrane
How thick is the cornea in different species?
-1/2 mm thick in dogs and cats
1 mm thick in horses
What is the limbus?
area between the cornea and the sclera/conjunctiva
How is the corneal epithelium attached to its basement membrane?
via hemidesmosomes
What are the characteristics of the corneal stroma?
-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
What are the characteristics of the corneal endothelium?
-pumps excess fluid out of the cornea
-single cell layer
What are the characteristics of corneal innervation?
-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
Why are superficial eye injuries more painful than deep injuries?
-nerve ending are just under the epithelium
-deep lesions destroy the nerves, causing less pain
Why do brachycephalic breeds have less of a response to eye injuries compared to other breeds?
brachycephalic breeds have less nerve concentration in the eye compared to other breeds
What are the functions of the cornea?
-support intraocular contents
-transmit light
-refract light
How does the cornea receive nutrients?
-aqueous humor delivers glucose, amino acids, vitamins, and other nutrients
-tears and palpebral conjunctiva supply oxygen (mainly tears)
What are the mechanisms that allow the cornea to maintain clarity?
-avascularity
-no pigment
-non-keratinized epithelium
-highly organized collagen fibril arrangement
-relative dehydration
-tear film
What are the ways in which the cornea responds to disease?
-edema
-cellular infiltration
-scar formation
-pigmentation
-vascularization
-keratinization
-secondary uveitis
What is corneal edema?
influx of fluid into the stroma as a result of endothelial damage and/or loss of epithelium
Which conditions can cause corneal edema?
-glaucoma
-ulceration
-uveitis
-endothelial dystrophy
-lens luxation
What can lead to WBC infiltration of the cornea?
-infected corneal ulcers
-immune-mediated disease
-neoplasia
What leads to scar formation/fibrosis?
abnormal arrangement of collagen fibers
What are the characteristics of corneal pigmentation?
-indicates chronic disease
-causative disease can be active or inactive
-rarely goes away 100% after resolving underlying cause
What are the characteristics of corneal vascularization?
-indicates active chronic disease
-takes 7-10 days for vessels to start growing to a visible point
-grow 1-2 mm per day
What are ghost vessels?
vessel tracks that remain in the eye without blood after the disease that caused vascularization resolves
What are the characteristics of keratinization?
-normally non-keratinized epithelium becomes keratinized
-seen with dry eye
-can be reversed
What are the characteristics of secondary uveitis?
-inflammation inside of eyeball
-results from axonal nerve reflex
What are the two methods of stromal defect healing?
-avascular: scarring with no blood vessels; collagen reforms after 6-12 months
-vascular: greatest amount of scarring; blood vessels visible
What are the three layers of the corneal epithelium?
-basal cells
-wing cells
-squamous cells
What are the characteristics of the epithelial basal cells?
-deepest layer
-single cell thickness
-layer that attaches to basement membrane via hemidesmosomes
-only epithelial layer to undergo mitosis
What is the epithelial wing cell layer?
middle transitional layer between the basal cells and squamous cells
What are the characteristics of the epithelial squamous cells?
-anterior layer
-contains microplicae and microvilli on surface to stabilize tear film
-tight junctions between cells limits permeability
What are the steps of healing for epithelial defects?
-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
What are the steps of avascular healing for stromal defects?
-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
What are the steps of vascular healing for stromal defects?
-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
