cornea Flashcards
corneal histology
A-epithelium
B-stroma
C-Descemet’s membrane
D-endothelium
thickness: 500 to 800 um
corneal epithelium
25 to 40 um in domestic carnivores
2-4x thicker in ungulates
nonkeratinized stratified squamous (G)
single layer of basal cells (A)
richly innervated (H)
hemidesmosomes
hydrophobic
corneal stroma
90% of corneal thickness
collagen
nerves are located in anterior portion
hydrophilic
descemet’s membrane
basement membrane for endothelium
acellular
PAS +
hydrophobic
Endothelium
single cell layer
hexagonal cells-minimal to no regeneration
Na+/K+ ATPase pump-keep fluid out of cornea
normal cornea
clear, colorless
smooth, hydrated
nutrition-precorneal tear film, aqueous humor
functions: light refraction, transmission of light
What allows the cornea to function properly
lack of pigment
lack of blood vessels
nonkeratinized epithelium
relatively low cell density
surface irregularities smoothed by mucin
relative dehydration
specific arrangement of stromal collagen
corneal deturgescence
hypertonicity of precorneal tears
hydrophobic epithelium
endothelium-most important factor with a Na+/K+ ATPase pump and tight intercellular junctions
collagen arrangement
parallel lamellae
close, regular spacing of lamellae
minimal light scattering
if not parallel will cause a glare
response to disease
epithelial metaplasia-keratinization, pigmentation (melanin), squamous metaplasia
inflammation-vascularization, edema
corneal ulceration
deposits into the cornea
necrosis
Corneal edema
often cobblestoned appearance
edema in the interlammellar spaces
focal implies epithelial disruption-superficial corneal ulcer
diffuse implies endothelial compromise-uveitis, glaucoma, deep corneal ulcer
corneal fibrosis
wispy grey
White blood cells in cornea
yellow/cream
cornea lipid and mineral deposits
sparkly
corneal melanosis
due to chronic irritation
corneal vascularization
indicates chronicity
superficial vessels and deep vessels
vascularization: superficial vessels
ocular surface disease
long thin branching “trees”
vascularization: deep vessels
deep corneal disease or intraocular disease
short, wider, little branching, “hedges”
diagnostic algorithm for patients with corneal vascularization
corneal healing: Epithelial defects
includes defects of epithelium only or epithelium and anterior 25% of stroma
the epithelial cells flatten and sliding around the wound margin to heal the area
epithelial cells can undergo mitosis
Corneal healing: stroma
involves >25% of stroma
epithelial healing occurs
fibroplasia occurs (ie resting stromal keratocytes undergo activation to become fibroblasts)
collagen is synthesized and reorganized
angiogenesis occurs if lesion is deep, infected or chronic
slow and imperfect–>reduced corneal transparency
corneal healing: Full thickness defects
wound selead with fibrin plug and corneal edema
WBC migrate in via tears, aqueous and corneal vessels
epithelium slides over to cover defect
stromal healing occurs
endothelial cells slide and some mitosis occurs followed by Descemet’s membrane formation
Examination and dx testing
transillumination
slit beam
STT
TFBUT
Flurescein stain
Cytology, C&S
Examination and Dx testing: transillumination
opacities will block light passage
alter the angle of light often to see differences in opacities
reflections on the cornea indicate hydration and presence of irregularities (may look mottled, crisp)
Examination and dx testing: slit beam
Purkinje image 1 is cornea
If lesion is in front part of image, it is an subepithelial lesion
if lesion is in back part of image, it is on the endothelium
can determine depth of lesion
Examination and Dx testing: STT
for quantative tear film evaluation
normal in dogs >15 mm/min
cats-variable
Examination and dx testing: TFBUT
for qualitative tear film disorders
normal ~20 sec in dogs, ~16 sec in cats
Examination and dx testing: Fluorescein stain
adheres to hydrophilic stroma-ID corneal ulcers
apply anywhere on ocular surface except cornea
do not dilute in >0.5 ml eye wash
use cobalt blue filter to improve visualizatino of uptake
Examination and dx testing: Cytology, C&S
swab, spatula lesion
topical anesthetic required
ID microogranisms
chacterization of corneal infiltrates
Dermoid
normal tissue in abnormal area
common locations: lateral limbus, third eyelid, eyellid
refer to ophthamologist
Corneal dystrophy
inherited subepithelial deposits
purebred dogs
usually appear by 2 years of age
lipid
bilateral
cystalline, oval opacities in central cornea
finite size
rarely results in visual compromise
r/o systemic hyperlipidemia
no tx
diagnostic algorithm for corneal lipid and mineral deposits
dx algorithm for corneal ulceration
sequalea of corneal ulceration
infection
globe rupture
pain
reflex uveitis
clinical signs of corneal ulceration
blepharospasm
epiphora
rubbing at eyes
conjunctival hyperemia
episcleral congestion
cheomsis
ocular discharge
older ulcers: corneal edema and vascularization
corneal cellular infiltrate
uneven corneal surface, divoting
principles of corneal ulceration therapy
remove underlying cause
topical abx
pain management
anti-inflammatory therapy
prevention of self trauma
secondary complications
topical abx therapy
prevent/tx infection
normal flora source of opportunistic infection
broad spectrum
pain management of corneal ulcers
topical atropine-paralyzes ciliary body to prevent muscle spasm, use loweset effective dose
topical preservative free 1% morphine
anti-inflammatory therapy for corneal ulcers
use if significant anterior uveitis is present
oral administration preferred
topical steroids CI
topical NSAIDs may potentiate collagenolysis
prevetation of self trauma for corneal ulcers
E-collar
doggles
optivizor
secondary complications
elevated risk of rupture with stromal loss
collagenolysis
infection
follow up for corneal ulcers
recheck 5-7 days
repeat ophthalmic examination with fluorescein stain
negative-disconintue meds and E-collar removed
positve: continue tx, recheck within 7 days
simple corneal ulcer
acute
loss of epithelium only
not infected
should heal within 7 days
tx: topical abx, +/- pain management
complicated corneal ulcer
does not heal within 7 days +/or stromal loss
persistent underlying cause
indolent corneal ulcer
aka spontaneous chronic corneal epithelial defect, boxer ulcer
abnormal attachments between epithelium and anterior stroma
Not infected
predisposed: older dogs, boxers, corgis
dx of indolent corneal ulcer
chronic hx
signalment
loose epithelial edges, superficial, no evidence of infection
medical tx for indolent corneal ulcers
topical abx
pain control
corneal lubrication
corneal debridement and grid keratotomy
contact lens placement
e-collar/doggles/optivizor
corneal debridement and grid keratotomy
removal of hyaline acellular zone
exposes stroma
promotes formation of attachments with epithelium
85% chance success
follow up for indolent corneal ulcer
recheck 2 weeks
remove contact lens
fluorescein stain-negative stop tx, positive-repeat debridement and grid keratotomy (up to 2-3 times)
refer if not healing
complicated corneal ulcer
chronic or have stromal loss, with concurrent underlying ophthalmic disease
includes: indolent, deep, melting and lacerations/perforations
deep corneal ulcer
stromal loss
depth assessed by slit beam
significant uveitis
assume infection
risk of globe perforation
dx for deep corneal ulcer
ophthalmis exam
cytology
C&S
Descemetocele
only Descemet’s mebrane and endothelium intact
risk of perforation immediate
descemet’s membrane will not retain fluorescein stain
medical tx for deep corneal ulcers
solutions only!
abx-do C&S but start abx prior to results, okay to use big guns such as fluoroquinolones
anti-inflammatory & analgesic-topical atropine, topical morphine, oral NSAIDs
E-collar, doogles, optivizor
refer for surgical graft
melting corneal ulcers
collagenolysis occurring
cornea becomes white/yellow and friable or liquid
can progress rapidly
significant uveitis
assume infection
melting corneal ulcers dx
ophthalmic exam
cytology
C&S
melting corneal ulcer tx
aggressive therapy
solutions only
abx q 1-2 h for 1-2 days, then q6h
pain control: topical atropine and morphine, oral NSAIDS
decrease uveitis-no topical steroids!
protease inhibitors-N-acetylcysteine, EDTA, doxycycline, serum!
E-collar, doogles, optivzor
refer for surgical graft
corneal lacerations and perforations
full thickness corneal injury
trauma
progression of deep and melting corneal ulcers
px guarded when there is lens involvement, hyphema, laceration size, limbal involvement, posterior segment involvement
urgent referral
corneal lacerations and perforations tx
aggressive medical tx
laceration repair
+/- FB removal
+/- surgical graft
+/- cataract sx
enucleation
Feline corneal ulcers
FHV-1
dendritic corneal ulcers
stromal keratitis
principles of ulcer therapy in cats
remove underlying cause
abx therapy-must be able to kill C. felis and Mycoplasma
pain management
anti-inflammatory therapy
prevention of self-trauma
address secondary complications
antiviral therapy
FHV-1 Therapy: mucinomimetic lacrimomimetics, antivirals, L-lysine, decrease stress
eosinophilic keratoconjunctivitis
unknown cause-maybe immune-mediated
concurrent corneal ulceration common
eosinophilic keratoconjunctivitis: clinical signs
conjunctivitis, raised, white to tan corneal plaques, superficial corneal vascularization, corneal edema
purkinje image 1 slightly elevated
eosinophilic keratoconjunctivitis: dx
dx: appearance, cytology-eos, mast cells, PMN, hyperplastic or dysplastic epithelial cells
eosinophilic keratoconjunctivitis: tx
antivirals
abx
tear film supplementation
anti-inflammatory/immunosuppressive meds-okay to use if ulcer present
eosinophilic keratoconjunctivitis:px
recurrence is common
some cats req long term therapy
corneal sequestrum
corneal necrosis
discoloration ranges from light brown to black
corneal sequestrum tx
address/remove source of irritation
treat corneal ulcer
treat uveitis and pain
refer for keratectomy and corneoconjunctival transposition
recurrence in 33%
pannus
aka chronic superficial keratitis
immune-mediated inflammation of the cornea with melanosis and/or fibrovascular proliferation
predisposed: GSD, greyhound
exposure to UV light worsens disease
usually bilateral
pannus presentation
bilateral, progressive infiltration of the corneas
can be blinding
third eyelid sometimes involved
most lesions start laterally
pannus therapy
require for life to minimize progression
immune suppression/anti-inflammatory: Prednisolone or dexamethasone, Cyclosporine A
limit exposure to UV light
pigmentary keratitis
bilateral, progressive melanosis and keratitis
brachycephalic ocular syndrome
how to differentiate pigmentary keratitis from pannus
breed
facial conformation
pigment distribution-medially
pigmentary keratitis: tx
eyelid sx
address underlying cause-lubrication, anti-inflammatories, medial canthoplasty
corneal deposits
usally subepithelial
may or may not be associated with ocular irritation, ocular disease or systemic disease
causes of lipid/mineral deposits in dogs
genetics (corneal dystrophy)
ocular inflammation-keratitis, uveitis
steroid keratopathy
hyperlipidemia
endocrinopathy
dx testing with corneal deposits
if bilateral, symmetrical in young purebred dog-corneal dystrophy-no tx
r/o endocrinopaties
checks serum cholesterol, triglycerides
tx for corneal deposits
often no therapy
diet change
chelation therapy if mineral
keratectomy
