Cornea Flashcards
what keeps the cornea dehydrated
epithelium - barrier to tear film
endothelium - active pump and barrier to aqueous humor
what 4 factors keep the cornea clear
avascular
non-mylinated nerves
dehydrated
ordered cell arrangement
how long does epithelialization take to occur
7 days or less (even wirh complete epithelial loss)
stromal healing results in _____
fibrosis/scarring
this takes days to weeks
what is a facet
non-staining depression in the cornea
Often, the epithelium often slides over remodeled stroma before it becomes level with surrounding epithelium
how long does it take a descemetocele take to heal
weeks to months
why referral and surgical repair is recommended
blue corneal opacity =
edema
2 possible causes of blue corneal edema
epithelial barrier disruption - tear film entry into hydrophilic stroma
endothelial barrier/pump disruption
3 ways endothelial barrier/pump can be disrupted
focal loss
generalized reduction in number
generalized reduction in function - glaucoma, uveitis
what causes red corneal opacity
corneal neovascularization
2 sources of red corneal opacity
superficial neovascularization
deep neovascularization
superficial neovascularization occurs with
KCS, eyelid conformation or hair abnormalities, superficial corneal ulcers
how long does it take for superficial neovascularization to occur
3 days from insult to start growing vessels
progress ~ 1mm per day
what is an indication of chronic stimulation leading to superficial neovascularization
granulation tissue causing a dense raised collection of superficial vessels
what are ghost vessels
non-perfused, empty vessels
occurs when stimulus/irritant has been removed
what is ciliary flush and when does it occur
360º deep neovascularization
occurs with uveitis
white corneal opacity with grey or wispy features indicates
fibrosis
white corneal opacity with yellow or green hue indicates
white blood cell infiltration
white corneal opacity that is crystalline or chalky indicates
mineral or lipid - dystrophy, degeneration
WBC infiltrates detected or not detected
characterisitics of WBC infiltrate
painful
associated with severe corneal disease
often associate with uveitis
signals corneal infection
this corneal opacity is due to
corneal fibrosis
dull white; corneal scar from previous corneral laceration
characteristics of corneal fibrosis
non painful
corneal scarring from previous keratitis
involves contracture of lamellar stromal collagen
what is causing the opacities in the pictures below
cyrtalline white - corneal lipid degeneration
chalky white - corneal calcific degeneration
corneal degeneration
can be lipid or mineral
secondary to: primary corneal disease or systemic disease
corneal dystrophy
most often lipid
2 causes of brown or black corneal opacities
pigment (melanin) - epi/endothelial
feline corneal sequestrum
what dis?
feline corneal sequestrum
epithelial corneal pigment
origin - conjunctival melanin
occurs as a result of chronic keratitis
esp. in brachycephalic breeds
endothelial pigment
origin - uveal (iris) melanin
occur congenitally (persistent pupillary membranes) or aquired (anterior synechial and uveal cysts)
what is the only cause of tan or greasy punctate in the cornea
keratic precipitates
what is the classic pattern of keratic precipitates
clear of precipitates dorsally
small precipitates at mid cornea
larger and larger precipitates as you move ventrally
this is helpful
but seriously…look at it
4 brachycephalic risk factors for corneal ulcers
ocular prominence
decreased corneal sensitivity
adnexal abnormalities
tear film abnormalities
T/F topical steroids can be used in the treatment of ulcerative keratitis
False!
never use any types of topical steroid in cases of ulcerative keratitis, cause delayed healing and enhanced corneal destruction
what consitutes a superficial corneal ulcer
loss of epithelium with no stromal loss
simple “uncomplicated” superficial corneal ulcers
superficial corneal ulcer that heals in 7 days or less
causes of superficial corneal ulcers
irritants - foreign body, tear film abnormalities, adnexal abnormalities
infection - herpes (cats)
trauma
treatment of simple superficial corneal ulcers
e collar!
broad spectrum antibiotics 3-4x/day
atropine 1-2x/day or until pupil stays dilated
recheck in 5-7 days
3 possible causes of complicated/complex corneal ulcers
indolent ulcer
persistent irritant (underlying cause has not been identified/treated)
infection
Indolent ulcers (aka spontaneous chronic corneal epithelial defect) signalment/ history
middle age to older dogs - NOT CATS
boxers
corneal ulcer that won’t heal - will take months is left untreated
diagnosis of indolent ulcers
test epithelium with cotton tiped applicator
normal epithelium will not debride easily
treatment of indulent ulcers
debridement! - reset relationsho between epithelium and stroma
once debrided - treat typucally similar to simple superficial corneal ulcers
what is the most important part of your approach to corneal ulcers
trying to find and treat the underlying cause (if possible)
3 possible infectious causes of complex corneal ulcers
FHV-1 - Most Common
early bacterial (cats and dogs)**
early fungal (cats and dogs)**
**This is where we transition into deep corneal ulceration as bacteria especially have affinity for stroma**
what features indicate which complex category this dog’s eye falls into
fluorescein “halo” - staining under the epithelial edge
indicates indolent ulcer
what is the most likely cause of this cats complex ulcer
Herpes!
most common cause of non-healing ulcer in a cat is FHV-1
why should you never perform ASP, GK, or DBD on cats with corneal ulcers
feline corneal sequestrum often occurs
T/F ASP, GK, or DBD should never be performed on infected ulcers
True
risks a severe progression of the infection
what is the most common ophthalmic condition seen in practice that will require a decision of whether or not to refer to specialist
deep (stromal) corneal ulcer
99% of deep (stromal) corneal ulcers have ______
corneal infection
bacterial or fungal (mostly horses)
collagenolysis
enzymatic destruction or corneal collagen
keratomalacia
softening or “melting” of corneal stroma due to collagenolysis
from bacterial/fungal and neutrophil enzymes
3 most common bacteria involved in deep corneal ulcers
Staphylococcus spp.
Streptococcus spp.
Pseudomonas aeruginosa - most common cause of melting
what is an important identifying feature of stromal ulceration
reflux uveitis
clinical signs of reflex uveitis
miosis
aqueous flare
diffuse corneal edema
hypopyon or hyphema
necessary diagnositics for deep corneal ulceration
STT - more important in normal eye
fluorescein stain
topical anthesia
cytology
aerobic culture
tonometry - avoid in fragile eyes
treatment of deep corneal ulceration
e-collar
antibacterial therapy
anti-collagenase therapy
reflux uveitis and pain management
+/- surgical management and referral
antibiotics used to treat deep corneal infections
cephalosporins
neomycin polymixin B Gtamicidin
fluroquinolones and aminoglycosides
high frequency of application (q1-2hrs)
3 indications for oral antibiotics with deep stromal ulcers
ulcer has become vascularized
cornea is close to perforation or has perforated
iatrogenic vascularization
anti-colagenase therapy options
autologous serum
1% EDTA solution
10% N-acetycysteine
at lease every 2-4 hours
pain management from reflux uveitis
atropine - paralyzes ciliary body (tx until pupil is dilated; 1-2x per day)
+/- oral anti-inflammatory and pain management (NSAID, tramadol)
3 guidelines for referral/surgical repair
ucler has 50% or greater stromal depth
ulcer is failing aggressive medical therapy
descemetocele or perforation
what dis?
Pannus aka chronic superficial keratitis
raised granulaton tissue
