Final Exam - Cornea Flashcards
what is ciliary flush (neovascularization)?
360° degree deep corneal neovascularization that is pathognomonic for uveitis - these vessels arise in the cornea from an intraocular or deep origin
what is corneal edema?
only blue opacity!!! appears heterogenous or fluffy
what are the only 2 mechanisms that cause corneal edema?
epithelial disruption or endothelial disruption
if you see focal edema as a part of corneal edema, what conditions should you think of?
superficial ulcers, anterior lens luxations, & early corneal endothelial dystrophy
if you see diffuse edema as a part of corneal edema, what conditions should you consider?
think of glaucoma, stromal ulcers, uveitis, endothelial degeneration, or advanced endothelial dystrophy
if you see bullous keratopathy as a part of corneal edema, what conditions should you think of?
diffuse edema that is chronic & severe that can supersaturate the corneal stroma causing sub-epithelial blisters to develop (ulcers frequently occur spontaneously)
what is corneal fibrosis?
corneal scarring - results from stromal collagen contracture & appears as a dull/wispy white, may see ghost vessels from past keratitis, non-painful condition
what is corneal dystrophy/degeneration?
dystrophy most often involving corneal lipids & appears glittery/shiny appears glittery/shiny with degeneration most often involving calcium & appears gritty/chalky - calcific degeneration more often associated with ulceration & pain
what is a descemetocele?
stromal ulcer that reaches the depth of descemet’s membrane where corneal epithelium & stroma are lost
what is deep corneal vascularization?
vessel pattern that occurs in response to deep disease processes (deep/infected ulcers & uveitis) - these vessels are usually straight, can’t be seen crossing the limbus, & don’t extend as far across the cornea as superficial neovascularization
what is a facet?
loss of corneal stroma with intact overlying epithelium, non-staining depression in the cornea - occurs because epithelialization progresses more rapidly than a stromal healing
what is feline corneal sequestrum?
unknown cause of brown or black discoloration - condition results from chronic corneal irritation and/or ulceration
what is the most common cause of feline corneal ulceration?
feline herpesvirus
what is hypopyon?
sterile white blood cell inflammatory reaction within the eye that often settles within the ventral anterior chamber with gravity
what does it mean if hypopyon is present alongside a corneal ulcer?
indicates stromal involvement & infection - emergency!!!
what is keratitis?
inflammation of the cornea
what are keratic precipitates?
cellular adhesions to the endothelium that are pathognomic for uveitis that have a classic appearance that is easily recognized with tiny dots from the mid-portion of the cornea that become larger & denser in the ventral cornea
what is keratomalacia?
corneal melting/melting ulcer/collagenolysis - bacterial/fungal/white blood cell associated enzymatic dissolution of the corneal stroma leading to a creamy, softened appearance to the corneal stroma - medical emergency
what is the limbus?
360° junction between the cornea & sclera/conjunctiva which is the migratory starting point for wound healing & many corneal pathologies - deep to the limbus, the cornea is at its closest point to the uvea (iris) also the site of epithelial stem cells, new blood vessels, & pigment
what is reflex uveitis?
uveitis that is triggered by corneal ulceration specifically - infected ulcers trigger severe reflexive uveitis where as non-infected ulcers trigger mild reflexive uveitis - used to distinguish non-emergent from emergent!!
what does the superficial cornea refer to?
pre-corneal tear film & epithelium, so superficial ulcer indicates a loss of epithelium only (important distinction from stromal qualifier)
what is superficial corneal neovascularization?
vessel pattern seen in superficial disease processes - think of KCS, eyelid disorders, feline herpes, & superficial corneal ulcers - vessels are tree like in appearance & can often be seen crossing the limbus with active vessels fully perfused indicating active/poorly controlled inflammation
what does stromal refer to in regards to the cornea?
entire corneal stroma - loss of stroma and/or presence of white blood cell stromal infiltration is often painful & signals infection - medical emergency!!!
what is white blood cell corneal infiltrate?
white category of corneal opacity that is a sign of active inflammation (keratitis) that is often painful & signals infection with its presence indicating an emergency
what do white blood cell corneal infiltrates look like?
green in appearance & most commonly observed in equine stromal abscesses & cases of corneal melting (keratomalacia)
what are the 4 primary layers of the cornea?
- epithelium - hydrophobic, repels fluorescein 2. stroma - hydrophilic, retains fluorescein 3. descemet’s membrane - hydrophobic, repels fluorescein 4. endothelium - not involved in fluorescein staining
what qualifies superficial & deep lesions in the cornea?
superficial - epithelial disruption, less emergent deep - stromal disruption/infiltration, always emergent!!!!!
which one represents a surgical emergency, medical emergency, & medical/surgical emergency?
left - surgical emergency, discuss referral
middle - medical emergency, high frequency treatment
right - medical/surgical emergency, discuss referral
what are the 4 contributing factors of how the cornea stays clear?
- avascular (in health - vessels only appear with inflammation) 2. non-myelinated nerves, densest network of nociceptive nerve fibers in the body located deep to the corneal epithelium 3. dehydrated - epithelium is the barrier to the tear film while endothelium has the active pump & barrier to aqueous humor 4. ordered cell arrangement that allows complete transmittance of light (in health)
what is the reason for why we can appreciate corneal opacities?
disruptions to the ordered cell arrangement reflects, scatters, or absorbs light
how does the epithelium heal in superficial corneal ulcers?
- epithelial breach is very painful!!! stroma will take up fluorescein at diagnosis 2. hemidesmosomes degrade & the epithelium is set up to slide & rapid cell division occurs at the limbus 3. epithelium slides over the ulcer 4. fluorescein stain is no longer taken up & the animal is comfortable 5. epithelium anchors itself to the stroma via hemidesmosomes & an indolent ulcer is avoided!
how long does it take for a superficial ulcer to heal?
7 days or less even with complete epithelial loss
how does the stroma heal for deep corneal ulcers?
- stromal cells (keratocytes) transform into contractile cells 2. these cells fill the defects 3. ulcer then epithelializes 4. stromal contracture causes disorganized of the ordered collagen resulting in a scar that we call corneal fibrosis
how long does it take for a stromal ulcer to heal?
days to weeks
what causes the development of a facet?
often, the epithelium slides over the remodeled stroma efore it becomes level with the surrounding epithelium - so facets, are indicative or previous deep/stromal corneal ulcers that are generally associated with comfort!!!!
how does a descemetocele heal?
limited & very slow (takes weeks to months) - vision threatening complications are likely with medical management!!!! surgical referral should be discussed!
epithelial barrier disruption is more likely to cause what corneal opacity?
blue corneal opacity - focal edema
endothelial barrier/pump dysfunction is more likely to cause what corneal opacity?
blue corneal opacity - diffuse edema
glaucoma, stromal ulcers, uveitis, endothelial degeneration/dystrophy, chronic/severe = bullous keratopathy
what causes should you consider if you see focal edema causing blue corneal opacity?
superficial ulcers, anterior lens luxations, & endothelial dystrophy
what causes should you consider if you see diffuse edema causing blue corneal opacity?
glaucoma, stromal ulcers, uveitis, endothelial degeneration, or endothelial dystrophy (advanced), & chronic & severe (bullous keratopathy)
if there is a blue opacity of the cornea, what does that mean?
edema!!!
what is the most common cause of focal corneal edema in dogs?
anterior lens luxations - progresses lateral to medial
what dog breeds are do we presume inheritance for focal edema from endothelial dystrophy?
chihuahuas, dachshund, & GSP
what are some examples of diseases that will cause diffuse corneal edema due to reduction in endothelial cell number & function?
- glaucoma (primary/inherited)
- stromal ulcer + reflex uveitis
- uveitis
- advanced endothelial dystrophy
what is the sequelae of diffuse corneal edema that is chronic & severe?
can lead to bullous keratopathy - spontaneous corneal ulceration ensures
what is the one cause with 2 important sources for red corneal opacity?
vessels
- superficial neovascularization - active, granulation tissue, inactive, or ghost vessels
- deep neovascularization - ciliary flush if 360°
what is the pattern significance of superficial corneal neovascularization?
stages of activity provide us a disease timeline
pathway of superficial vessels often points to the origin of inflammation
what causes superficial corneal neovascularization? how long does it take for superficial neovascularization to start? how much does it grow a day?
causes - think of superficial stimuli (adnexal diseases such as distichia, entropion, lagophthalmos, etc. & ocular surface disorders such as KCS, SF corneal ulcers, pannus, etc)
takes ~3 days from the insult to see vessels growing
progress 1mm/day
T/F: vessels that cross the limbus are a common feature of superficial neovascularization that is not found in deep neovascularization
true
what is seen on these eyes that is a feature of superficial neovascularization of the cornea?
granulation tissue
what is the difference between inactive & ghost vessels?
inactive - perfused, but regressing vessels
ghost vessels - non-perfused/empty vessels
what are the 2 most common causes of deep neovascularization?
uveitis
deep corneal ulceration (+/- reflex uveitis)
what is ciliary flush? what disease does it only occur in?
360° deep neovascularization - seen only with deep neovascularization
what is the timeline for development of deep vascularization?
~3 days from the insult to start growing vessels
progress is slower than superficial vessels
what kind of vascularization is shown here?
deep neovascularization - crown of thorns
what are the 3 variations of white corneal opacities?
- white with yellow or green hue - white blood cell infiltration
- white with gray or whispy features - fibrosis
- crystalline or chalky white - mineral or lipid due to dystrophy or degeneration
the _______ part of the cornea is most susceptible to degradation
stroma
to identify the basic pathologic changes of the cornea, what feature are you looking at?
the color change!!!
what does a blue color change of the cornea signify?
edema is the underlying pathology
what does a red color change of the cornea signify?
neovascularization is occurring - consider superficial or deep
what does a white color change of the cornea signify?
corneal dystrophy - lipid, non-painful, common in dogs
corneal degeneration - ulcerates, primary corneal disease or systemic, acquired
what does a brown/black color change of the cornea signify?
melanin - either epithelial (chronic ocular surface irritation) or endothelial (thick, uveal cysts or iris tissue endothelial adhesion)
feline corneal sequestrum - chronic ocular surface irritation such as herpes
what does a tan or greasy punctate color change of the cornea signify?
keratin precipitates, cellular & fibrinous adhesions to the endothelial surface (uveitis) - ventral, big dots on bottom & small dots on top
what factors make brachycephalic breeds more likely to experience corneal ulceration?
- ocular prominence
- decreased corneal sensitivity
- eyelid abnormalities
- KCS predisposition
how should an e-collar be constructed for a dog with ulcerative keratitis?
need it to extend just beyond the nose when pushed back to the shoulders & be firm
what are some causes of simple superficial corneal ulcers? how long does it take to heal?
causes - eyelid/hair irritant, lagophthalmos, KCS, trauma, & herpes in cats
no complicating factors - should heal in 5-7 days
what does SCCED mean?
spontaneous chronic corneal epithelial defect - indolent ulcer
what dogs are predisposed to getting indolent ulcers?
middle aged boxers
in order of most toxic to least toxic, what drugs should be avoided for animals with corneal ulceration? why?
proparacaine - okay to use in exam room!!!!
NeoPolyDex ointment/suspension
prednisolone
diclofenac (nsaid)
flurbiprofen (nsaid)
all of these meds will delay healing & enhance corneal destruction!!!
why do we need to make empiric selections for drugs for stromal ulcers of the cornea?
the stroma is very susceptible to rapid & complete destruction (<24 hours) following the establishment of a bacterial infection - can’t wait for cytology/culture to direct targeted therapies
what guidelines should you follow for empiric selections for antibiotics for corneal ulcers?
superficial - prophylactic abx selection & frequency
stromal - rescue abx & frequencies
breed considerations - stromal ulceration is 10X more likely in a small brachycephalic breed relative to larger breeds
what is the definition of a prophylactic antibiotic for a superficial corneal ulcer? what frequency should be used?
broad spectrum abx that is intended to stop the proliferation of a normal ocular surface bacteria within the stroma of a superficial corneal ulcer
TID to QID - never less than 3X daily due to 1st order pharmokinetics & resistance concerns
what are your prophylactic abx options for superficial corneal ulcers?
all available as antibiotic ointments & solutions
erythromycin - well tolerated in cats
polymixin b oxytetracycline - terramycin
NeoPolyBac
NeoPolyGram
what 2 factors qualify a drug as a rescue antibiotic for deep corneal ulcers?
- abx that has historically demonstrated efficacy against the most common bacterial isolates from stromal ulcers
- abx that has a high degree of ocular penetration
what is the rescue frequency for abx for stromal ulcers?
6x daily during waking hours for outpatients
12-24X daily for hospitalized cases
what clinical assumption are you making when choosing rescue frequencies & selections for a corneal ulcer?
assuming the ulcer is stromal and/or at high risk to become stromal - examples of KCS & small brachycephalic patients!!!
what are your single drop rescue options for stromal ulcers? what are your two drop rescue options for stromal ulcers?
4th generation fluoroquinolones - moxifloxacin or gatifloxacin ophthalmic solution (convenience option)
2nd generation fluoroquinolones + topical cephalosporin - olfoxacin, ciprofloxacin, & 5% compounded cefazolin
what are the 3 possibilities for complex superficial ulcers?
- indolent ulcer - SCCED, most common
- persistent irritant
- early/insidious stromal ulcer
what is the pathology of dogs with indolent ulcers due to SCCED?
healing is altered because there is lack of epithelial adherence to the stroma
how do you diagnose an indolent ulcer?
test the epithelium with a q-tip - normal epithelium will not debride easily!!!!!
this is the classic staining pattern of what type of ulcer?
complex indolent corneal ulceration
what are the 2 important distinctions of therapy for complex indolent superficial corneal ulcers?
- healing depends on the mechanical debridement of the ulcer!!!!
q-tip debridement - 50% healed at 2-3 weeks
diamond burr - 80-90% healed at 2-3 weeks - follow up recommendations - recheck weekly & DO NOT REPEAT DEBRIDEMENT IF <14 DAYS FROM THE PREVIOUS DEBRIDEMENT!!!!!
what are the criteria for using a diamond burr for debridement of an indolent ulcer?
performed following proparacaine & CTA debridement
never <3.5mm tip
never >60 seconds
never for stromal ulcers!!!!!
what are the moderate to severe clinical signs associated with reflex uveitis?
miosis, aqueous flare, diffuse corneal edema, hypopyon/hyphema
what are the 3 most common bacterias that cause stromal ulcers?
staph spp - gram positive aerobic cocci
strep spp - gram positive aerobic cocci
pseudomonas aeruginosa - gram negative facultative anaerobic rod
what bacteria most commonly causes melting ulcers?
pseudomonas aeruginosa - gram negative facultative anaerobic rod
what is collagenolysis?
enzymatic destruction of corneal collagen
what is keratomalacia?
softening/melting of the corneal stroma due to collagenolysis from bacteria/fungi & neutrophil enzymes
what are the identifying features of stromal ulcerations?
inappropriate level of reflex uveitis, severe corneal edema, white blood cell infiltration, deep corneal vessels & episcleral injection, visible stromal loss/disruption, & malacia
T/F: in general, if you can see an ulcer with your naked eye, it is highly concerning for a deep, infected corneal ulcer
true
what is pictured here?
keratomalacia - cornea is softening
what are some supporting clinical signs for corneal perforation?
positive seidel test - active leaking
wrinkled corneal appearance, shallow anterior chamber, iris prolapse, fibrin plug, hyphema
what is the minimum diagnostic assessment that should be done for stromal ulcers?
stromal ulcers should be sampled cytologically & cultured anaerobically following instillation of proparacaine
cytology for empiric selection & culture to guide abx changes at follow-up
when should you add systemic abx for a patient with a stromal ulcer?
- ulcer has become vascularized
- cornea is close to perforation or has perforated
- iatrogenic vascularization
when do you offer referral for surgical repair for a stromal ulcer?
- 50% of greater depth & perforations
- cases that fail to improve at the first follow-up exam where rescue therapies are already being used
what is the most common surgical repair done on the cornea for stromal ulcers?
conjunctival pedicle flap procedure
what breeds are predisposed to pannus?
shepherds, shepherd crosses, & greyhounds
increased incidence in high altitudes & low latitude (increased UV light)
what is pannus?
immune mediated reaction to the epithelial surface (cornea & conjunctiva) that is non-painful but can be blinding!
what is seen on cytology that is supportive of pannus?
lymphocytes & plasma cells, blood vessels (granulation tissue), & pigment
what are the 2 categories that we split pannus in to?
- typical - corneal conjunctival origin
- atypical - third eyelid origin
what disease is shown here?
typical pannus (chronic superficial keratitis)
what is the treatment for pannus?
topical anti-inflammatory therapy - short term steroids or long term topical cyclosporine
UV light avoidance or protection
T/F: pannus is an example of a non-ulcerative keratitis
true
