Cornea Flashcards
What are the 4 layers of the cornea?
Epithelium
Stroma
Descemets membrane
Endothelium
How does the cornea stay clear?
Avascular Non-myelinated nerves Dehydrated - epithelium (barrier to tear film) -endothelium (active pump and barrier to aqueous humor) Ordered cell arrangement
How does the epithelium heal?
Epithelialization
Hemidesomosmes dreate
Epithelium set up to slide
Rapid cell division from the limbus—> slide to cover the ulcer
Epithelium becomes fixed to stroma as hemidesmososmes form
Takes 7 days to complete
How does a stromal ulcer heal?
Stromal cells (keratocytes) transform into contractile cells
Cells fill the defect
Ulcer then ‘epithelializes’
Stromal contracture causes disorganization of the ordered collagen, resulting in scar
What do you call a non—staining depression of the cornea?
Facet
— occurs when epithelium slides over remodeled stroma before it has become level with the surrounding epithelium
How does a descemetocele heal?
Vascular ingrowth = takes a long time
Scar formation (takes weeks to months)
Eventually the ulcer will re-epithelialize
Blue corneal opacity is caused by?
Edema
— epithelial or endothelial barrier disruption
Degree of corneal edema depends on what factors ?
Geographic size of the ulcer
Depth of ulcer
Reflex uveitis is present or not
What are causes of a generalized reduced function of the corneal endothelial barrier, resulting in a generalized edema?
Glaucoma
Uveitis
Red corneal opacity indicated?
Corneal neovascularization (can be superficial or deep)
Superficial —> granulation tissue and ghost vessels
Deep —> ciliary flush
What stimuli can induce superficial neovascularization?
KCS
Eyelid conformation
Hair abnormalities (entropion, distichia, trichiasis)
-> vessels move toward the offending stimulus
What do you call a dense, raised collection of superficial vessels on the cornea due to a chronic stimuli?
Granulation tissue
What are ghost vessels?
Non-perfused, empty vessels
Occurs when the stimulus/irritant has been removed (eg when a corneal ulcer)
What stimuli can cause a deep neovascularization ?
Uvititis
Glaucoma
Deep corneal inflammation/ulceration
What are causes of a white with yellow/green corneal opacity?
White blood cell infiltration
Eg deep stromal abscess or hypopyon due to reflex uveitis
What are causes of a white withe gray/wispy cornea?
Fibrosis
Eg dogs with healed corneal ulcer
What are causes of a crystalline or chalky white corneal opacity?
Mineral or lipid
- dystrophy
- degeneration
“Sparkly” opacities to the cornea are due to?
Corneal dystrophy = lipid deposits
T/F: corneal degeneration can be lipid or mineral deposits and often ulcerated
True
A disrupted specular reflection indicates??
Irregularity of the ocular surface
Brown opacities of the corneum?
Epithelial
— pigmentary keratitis (melanin)
Endothelial
— deflated uveal cysts
—anterior synechia from previous corneal perforation and iris prolapse
Black opacity in corneum of feline?
Feline corneal sequestrum
— necrotic corneal stroma
Occurs after chronic corneal ulceration often due to FHV1
You see tan/greasy punctuate in the cornea. What is this?
Keratoconjunctivitis precipitates — cellular and fibrinous adhesions to endothelial surface
Usually settles in the ventral corneal
What are 4 risk factors that predispose brachycephalic to corneal ulcers?
Ocular prominence
Decreased corneal sensitivity
Adnexal abnormalities (eg nasal fold trichiasis or lagopthalmos)
Tear film abnormalities
T/F: all animals with corneal ulcers should be treated with topical steroids and placed in an Ecollar
FALSE
NEVER give steroids to ulcer patients Cause -> delayed healing -> more corneal destruction -> increased risk of infection
But the E collar is a good thing
Loss of epithelium with no stromal loss is called?
Superficial corneal ulceration
What are causes of superficial corneal ulceration?
Irritants
- adnexal abnormalities
- tear film abnormalities
- foreign bodies
Infection
-herpesvirus
Trauma
What are the two classification of superficial corneal ulcers?
Uncomplicated/ simple — heals in 7 days for less by epithelialization
Complicated/complex — an ulcer that does not heal appropriately
What is the treatment for an uncomplicated superficial ulcer?
Ecollar
Broad spectrum antibiotics for 3-4x/day
+/- atropine
Recheck in 5-days
What are the types of complicated superficial ulcers?
Indolent
Persistent irritant
Infeciton
What is the signalment for indolent ulcers?
Middle aged and older dogs
Boxers!
Why do indolent ulcers develop?
Initial corneal injury with altered healing due to lack of adherence of epithelium to stroma (abnormal hemidesmosomes)
How can you test for indolent ulcers?
Test epithelium with cotton tipped applicator
- normal epithelium will not debride easily
Fluorescin halo — staining beyond epithelial ulcer margins
What is the treatment for indolent ulcers?
Debridement with sterile q-tip
50% will heal in 2weeks
If not healed in 2 weeks... Anterior stromal puncture OR Diamond burr debridement (These should never be not on infected ulcers!)
Topical treatment similar to superficial ulcers
- antibiotics
- +/- atropine
- +/- pain managment (NSAID or tramadol)
What is the most common cause of an infected superficial ulcer in cats?
Herpesvirus
T/F: most deep stromal corneal ulcers are considered complex, most are caused by infection
True
What is the pathogenesis of deep corneal ulcers?
Most due to infection (bacterial or fungal)
Collagenolysis — enzymatic destruction of corneal collagen
-> keratomalacia = softening of the corneal stroma due to collagenolysis
What are the most common bacteria causing deep corneal ulcers?
Staphylococcus spp
Streptococcus spp
Pseudomonas aeruginosa (most common cause of melting)
What is a reflex uveitis?
Ulcerative keratitis causing varying degrees of uveitis
Ophthalmic branch of CN V innervates both the cornea and uvea
Corneal irritation stimulates corneal nerves and also sends noxious stimuli back to the ciliary body -> release of inflammatory medications and breakdown of blood ocular barrier
Clinical signs of a uveitis?
Episceral injection
Diffuse corneal edema
Severe miosis
Turbid anterior chamber = aqueous flare
Why do we commonly see descemetoceles more commonly than deep corneal ulcers?
Loss of epithelium —> stoma extremely sensitive to proteases from fungi and bacteria
Progression of collagenolysis through the stroma is rapid
Descemets membranes is moderately resistant to these proteases
What clinical signs do you see with corneal perforation?
Wrinkled corneal appearance Shallow anterior chamber Iris prolapse Fibrin plug Hyphema
Positive Seidel test — active leaking
What diagnostics should you do in a case of deep stromal ulceration?
Schirmer tear test — more important in normal eye
Fluorescien
Topical anesthesia
Cytology —> guides initial therapy
Aerobic culture —> changes to therapy
Tonometry (avoid in fragile eyes)
What can you use to help in an ocular exam in a patient with a painful corneal ulcer?
Proparacaine
NEVER send home with client — repeated used is toxic to corneal and may result in melting corneal ulcer
When is surgery indicated in a patient with deep corneal ulcers?
When there is >50% stromal loss
— conjunctival pedicle flap
— 360 conjunctival flap
What are advantages and disadvantages of conjunctival pedicle flaps?
Provides immediate tectonic strength
Provides a blood supply for paternal antibiotic augmentation
Provides serum for anti-collagenolysis
Disadvantages— can cover visual axis
What is the protocol for medically treating deep corneal ulcers?
Topical antibiotics (4quadrant coverage)
- cephalosporins — gram positive and anaerobes
- fluoroquinolones or aminoglycosides — gram negatives and aerobes
Every 1-2hours for the first 2days
Systemic antibiotics (sometimes) Anticollagenase therapy (melting ulcers) Reflex uveitis and pain managing (atropine, NSAID/tramadol)
What are the indications for systemic antibiotics with corneal ulcers?
The ulcer is well vascularized
Cornea has perforated
Conjunctival flap was performed
What products can you use for anticollagenase therapy to treat a melting ulcer?
Autologous serum
EDTA
N-acetylcystine
