The Opaque Eye Flashcards
What are the three cell types of the corneal epithelium?
Basal cells, wing cells and squamous non-keratinised epithelium
What is the function of the basal cells?
Transient amplifying cells capable of mitosis with stem cells at the limbus
What is the function of the wing cells?
No longer mitotic and make up the second section of the epithelium with between 2 and 4 layers of cells
What is the function of the squamous non-keratinised epithelium?
Top section and is sloughed off with blinking
What are the methods of corneal epithelial healing?
Sliding movement
Vertical movement
Centripetal movement
When does sliding healing occur?
Minor damage to the top layer of the epithelium
How long does healing by sliding take?
24 hours
When does vertical movement occur?
After sliding movement and involves basal cell mitosis and deals with daily loss of cells/regaining thickness of epithelium
How long does vertical healing take?
1-2 weeks
What is the process of centripetal healing?
Path the epithelial cells take from the edge of the cornea at the limbus to the centre in the shape of a spiral
When is centripetal healing clinically significant?
If healing results in concurrent pigment production as this could obscure vision if it reaches the centre of the eye and covers the pupil
What is healing by sliding dependent on?
Corneal health, existence of limbal basal cells and basal lamina, species and age of the animal
What happens if there are no limbal stem cells?
Conjunctiva can provide the epithelium but this is opaque and can lead to symblepharon
Why does vascularisation occur in corneal epithelial healing?
Angiogenic factors are not well understood but inflammation is thought to be a stimulus
What process does vasculatisation occur by?
Inflammation stimulates and the vessels can coalesce to form granulation tissue and the vessels atrophy once the stimulus is removed
What are the two different types of blood vessels that form? How do you differentiate them?
Superficial = dichotomous Deep = straight and look painted on
Why is vascularisation important to corneal healing?
Blood vessels bring stabilising serum to protect against corneal melting, nutrients, growth factors and inflammatory cells as well as structural support for reconstruction/remodelling
How do vessels indicate chronicity?
Vessels take 2-4 days to bud and grow at 1mm/2days
What makes up the stroma?
Collagen lamellae made up of predominantly collagen I fibrils and keratocytes
What is the arrangement of the collagen fibres of the stroma?
Travel from limbus to limbus and are united and ordered by GAGs and kept relatively dehydrated so they are transparent
What chemokines are involved in stromal healing?
IL-1, EDGF, TNF-beta, collagenases and metaloproterases
What produces the chemokines?
The lacrimal gland as well as epithelial cells, stromal keratocytes, corneal nerves and leukocytes attracted to the wound
What is the role of monocytes, macrophages, neutrophils and T cells?
Destruction and clean up of damage
How does the initial scar form?
Keratocyte-mediated build up of collagen fibrils and their interconnections as well as ECM GAGs but these aren’t in the correct quantities/types/distribution
What can cause an imbalance in destruction and build up?
Tear film imbalance, iatrogenic causes, entropion, distichiasis, trichiasis etc
How long does stromal healing take?
Weeks for stroma to fill defect and months of remodelling
What is the structure of the endothelium?
Chicken wire pattern
What is the function of the endothelium?
It keeps stroma dehydrated by being a physical barrier and sodium - potassium pumps which put fluid back in the anterior chamber
What is a special feature of the endothelium?
Cells become larger when their neighbours die resulting in pleo/polymorphism with more sodium-potassium pumps
What happens if endothelial repair fails?
Corneal oedema
What can damage the endothelium?
Glaucoma, uveitis, anterior lens luxation, direct damage intra-operatively or by chemical damage as well as Primary Endothelial Degeneration
What is the difference between superficial and deep ulcers?
Superficial stain with fluorescin and look like a small scratch or graze
Deep don’t stain as stroma is gone and have a clear dark centre
What is collagenolysis?
Corneal melting
Can progress rapidly within hours or a handful of days and can result in perforation of the cornea
What is the treatment for superficial ulcers?
Allow time to heal themselves, check every 3-5 days, if not healing consider where the healing imbalance is occuring
What are the common problems with healing?
Tear film abnormalities (quantitative/qualitative), eyelid problems, third eyelid problems, brachycephalic effect, secondary infection or corneal melting
What are the key signs of no healing?
Lack of re-epithelialisation, stromal wound deepening and stroma devitalising
What are the diagnostic steps to follow if an ulcer isn’t healing?
STT-1 and an eyelid exam
What forms of protection are there for ulcers?
Elizabethan/buster collar
Tarsorrhaphy
TE/nicitating membrane flap
What is a tarsorrhaphy?
Horizontal mattress suture through eyelids using stents to protect eyelids. 1st exit suture and 2 entrance suture through meibomian gland to ensure you get tarsal plate
What antibiotics can be used to treat ulcers?
Fusidic acid gel, BID, mostly vs gram +ves
Chloramphenicol eyedrops, TID, good penetration, gram +ves
What other treatments can be used?
Serum eyedrops to prevent melting every 30 mins once started or TID to prevent melting occuring
Atropine to relax ciliary body and iris causing mydriasis, BID for 1-2 days
Preservative free viscous tears
What is the treatment for a descemetocoele?
Surgical repair
What is KCS and what causes it?
Keratoconjunctivitis Sicca
Primary or secondary to evaporation, drugs, anaesthetics and sedatives or neurogenic
What is Trend A of Primary Keratoconjunctivitis Sicca (KCS)?
0-2 years/6-8 years
More males than females
Non sterilised
Ulcerative keratitis in 50-72% with many rapidly perforating
What is Trend B of Primary Keratoconjunctivitis Sicca (KCS)?
5 years
More females than males
Lower incidence of ulcerative keratitis (4-22%) with most superficial
Why do central/paracentral ulcers perforate?
Diseased cornea, irritant still present, abnormal clearing due to increased thick mucoid discharge, change in bacterial flora or inflammatory cells in surface
What are the early surgical and medical treatments?
CLCT, conjunctival pedicle graft, topical ciclosporin, preservative free viscous tears, topical antibiotics, serum eyedrops
What is CLCT?
Corneolimboconjunctival transposition and uses a clear peripheral cornea leaving a clearer visual axis after healing than other techniques
When would you use a conjunctival pedicle graft and why?
For peripheral ulcers as its quicker although it doesn’t clear much over time but its not that important as its peripheral
What does SCCEDs stand for?
Spontaneous Chronic Corneal Epithelial Defects
What are the clinical signs of SCCED?
Loose epithelial edges, under-running of fluorescein dye, positive pulsed saline test
+/- corneal oedema, +/- ocular pain, +/- ulcerative damage
What are the causes of SCCED?
History of minor trauma, anterior stroma, PAS+ (staining technique), acellular zone with hyaline membrane, hyaline membrane interferes with epithelial adherence to the stroma
What is the surgical treatment for SCCED?
100% success with keratectomy and best outcome in cats
What treatments are contraindicated in cats?
Debridement and grid keratotome/superficial scrape
What is the medical treatment for SCCED?
Chloramphenicol TID +/- serum eye drops TID/QID
What is Feline Corneal Sequestrum?
Spontaneous, uni/bilateral, tan to black discolouration of superficial stroma, localisation varies with cause
What is the progression of Feline Corneal Sequestrum?
Darker plaque to neovascularisation to ulceration around the plaque
What are the theorised aetiologies?
Corneal trauma, tear film stability and goblet cell function, lower corneal sensitivity, lipid abnormalities and possible dessication or FHV-1
What is the treatment?
Superficial keratectomy +/- bandage lens +/- tarsorshaphy
Superficial keratectomy and grafting
How does FHV-1 infection occur?
Cats infected in kittenhood and virus lives in trigeminal ganglion and corneal tissue
What does FHV-1 cause?
Severe corneal ulcerative disease that recrudesces in times of stress, early ulcer is dendritic (pathognomonic) and progesses to more common geographical ulcer
What is the treatment for FHV-1?
Interferon and L-lysine
Antiviral eyedrops 4-6 x daily but very irritant
(systemic antivirals)
What is feline acute bullous keratopathy?
Unknown aetiology
Acute development of corneal oedema where cornea becomes soft and at risk of melting and perforation
What does facial nerve paralysis cause?
Loss of blink leading to interpalpebral fissure ulceration
How is facial nerve paralysis treated?
Tarsorrhaphy for 1-2 months as well as protective collar, topical antibiotic and preservative free viscous tears
