A Colour Guide to the Cornea Flashcards
What can cause vascularisation of the cornea?
Irritants
Chronic diseases such as canine LPI or pannue and feline eosinophilic keratitis
What colour does vascularisation make the cornea go?
Red/pink
What colour does oedema cause the cornea to turn?
Blue
What can cause corneal oedema?
Superficial corneal level (ulcers and vascularisation)
Intra-ocular disease such as uveitis, glaucoma, lens luxation
What colour do deposits and infiltrates turn the eye?
White/yellow
What deposits or infiltrates can colour the cornea?
Cholesterol/calcium
Scar
Abscess
Fluorescein
What colour does pigment make the cornea?
Brown to black
What can cause pigment in the cornea?
Irritants and chronic disease
Scar
Sequestra mainly in cats
Which eyelid and hair abnormalities can cause irritation to the cornea?
Entropion Ectropion Trichiasis Distichiasis Ectopic cilium
What is ectropion?
Where the eyelid comes away from the surface of the eye
What is entropion?
Where the eyelid curls into the surface of the eye
What is distichiasis?
Where a hair grows out of the meibomian gland
What is trichiasis?
Where facial hairs touch the surface of the eye
What is an ectopic cilium?
An eyelash that exits through the conjunctiva of the eyelid
Which dogs are more susceptible to medial lower eyelid entropion +/- canthus?
Brachycephalics
High prevalence in the pug
Which dogs are more susceptible to upper eyelid entropion?
Cockers, hounds etc.
Heavy ears and forehead
Which dogs are more susceptible to lateral upper and lower eyelid and lateral canthus entropion?
Shar-Peis
Which factors predispose to lateral lower eyelid entropion?
Young dogs, medium-large breed
Older cats
Blepharospasm
Which chronic infiltrative immune-mediated diseases cause corneal vascularisation?
Canine Lymphocytic Plasmacytic Infiltrate
Feline Eosinophilic Keratitis (can also affect horses and rabbits)
Which chronic non-infiltrative immune-mediated disease can cause vascularisation of the cornea?
Canine dry eye (Keratoconjunctivitis sicca)
What are the other names for canine lymphocytic plasmacytic infiltrate?
Corneal pannus (layer upon layer) Chronic superficial keratitis (CSK)
Which breeds are predisposed to canine lymphocytic plasmacytic infiltrate?
German Shepard Dogs
Greyhounds
Rottweilers
What can make canine lymphocytic plasmacytic infiltrate worse?
Sunlight, snow or high altitude
What are the signs of canine lymphocytic plasmacytic infiltrate?
Cellular infiltrate and vascularisation +/- pigment
Dorsolateral corneoconjunctiva usually affected first
How is cytology of canine lymphocytic plasmacytic infiltrate performed?
Proxymetacaine (0.5%) topical anaesthetic and then cytobrush and diff quik stain
What are the properties of proxymetacaine 0.5%?
OOA 30-60 seconds
DOA 15-30 minutes
Decreases blink, increased dryness, ulcer formation
What is seen if there is third eyelid involvement with canine lymphocytic plasmacytic infiltrate?
Depigmentation and hyperaemia
What species can eosinophilic keratitis affect?
Cats (mainly)
Rabbits
Horses
What are the signs of eosinophilic keratitis?
Cellular infiltrate and vascularisation with dorsolateral corneoconjunctival area usually affected first
Infiltrate is pink to white and in the form of plaques or clumps
Which cells are involved in eosinophilic keratitis?
Neutrophils
Plasma cells
Clusters of eosinophils - diagnostic
What can make eosinophilic keratitis difficult to diagnose?
Cellular infiltrate may uptake stain
What is the general treatment regimen for LPI and EK?
Topical immunomodulators starting with 4-6x daily then tapering off slowly over many weeks (reduce by 1x a day every 2 weeks)
Maintain at a minimum of 2x a day for 2-4 weeks and re-examine
May reduce to 1x a day or EOD for maintenance
Which topical immunomodulator is used to control LPI in dogs?
Topical ciclosporin but need to combine with a steroid to start with
Which topical immunomodulatory drug is used to control EK in cats?
Topical steroid (dexamethasone phosphate) Not ciclosporin as it is irritant in cats
What supports a diagnosis of canine keratoconjunctivitis sicca?
History of recurring persisting ocular surface problems
Clinical signs of conjunctivitis, surface dullness, mucus discharge, ulcers
Low Schrimer Tear Test - 1 result
What is the treatment for canine keratoconjunctivitis sicca?
Topical ciclosporin BID or SID, long term (for life)
Preservative free viscous tears
What are the characteristics of acute canine KCS?
Affects mostly young or old dogs
Less mucus and less hyperaemia than chronic cases
Often ulcerative
What are the characteristics of chronic KCS?
Scarring
Pigment changes
Vascularisation
How is KCS treatment success evaluated?
Improvement in at least 3 out of 5:
Mucus production, redness, comfort, keratitis, tear readings
How do ulcers turn the cornea red?
Develop a red bed of granulation tissue formed by coalescing blood vessels
Where do corneal blood vessels arise from?
Limbus
What does lipid infiltrate of the cornea look like?
Reflective white crystals in superficial stroma
What are the characteristics of primary lipid infiltrate (dystrophy)?
Most common
No vascularisation
In several breeds such as CKCS, Huskies
What are the characteristics of secondary lipid infiltrate?
Degeneration accompanied by vascularisation
Associated with chronic corneal problems
Associated with hyopthryroidism
What is the general progression of lipid infiltrate?
Slowly progressive
What is the treatment for lipid infiltrate?
Dietary control theorised by some to help slow down progression
Topical steroids and oestrus can speed up progression
Might be removed if large and blocking vision but non-painful
How does calcium infiltrate appear clinically?
Chalky, non-reflective white crystals in superficial stroma
May adopt a reticulated pattern
What is the pathogenesis of calcium infiltrate?
Secondary to degeneration
Associated with chronic corneal problems
Accompanied by vascularisation
What treatment is necessary for calcium infiltrate?
May need removal via keratectomy if painful as can spiculate and spicules break through the epithelium causing pain
What can cause corneal scarring?
Chronic keratitis, ulcerative keratitis and surgery
What is the clinical appearance of corneal scarring?
Non reflective, non crystalline, dull
What are the characteristics of corneal abscesses?
An accumulation of WBCs
Enzymes can lead to rapid collagen melting
Not a pocket of fluid as it can’t be drained
What causes corneal oedema?
Loss of epithelium
Loss of endothelium
Vascularisation resulting in leakage
What is the appearance of corneal oedema?
Blue mottled appearance
What is the pathogenesis of corneal oedema?
Loss of epithelium due to an ulcer
Endothelial damage due to increased intra-ocular pressure/inflammation/primary endothelial degeneration/contact
Vascularisation as developing vessels leak
What is the pathogenesis of pigmentary keratitis in pugs?
Associated with medial canthal and lower eyelid entropion
Overexposure of the cornea and conjunctiva
Occasionally associated with dry eye (KCS)
Very proliferative pigment response that starts medialy
Can be sight impairing to blinding by 2 years of age
What is the pathogenesis of sequestra in cats?
Idiopathic and spontaneous but associated with chronic irritation commonly in the central cornea or medially with medial lower eyelid entropion
What is the progression of sequestra of cats?
Light tan discolouration of superficial stroma, intact epithelium
Darkening of lesion, loss of epithelium, vascularisation, pain
Hardening and deepening of lesion
