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What are some unique characteristics of the equine cornea? (4)
- slower to heal
- more likely to become infected
- more likely to melt
- more likely to lose vision
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What are limitations of using topical steroids in the equine eye? (6)
- contraindicated in corneal ulceration
- increased risk of infection, esp fungal
- impair ocular surface immune response
- delay epithelialization
- potentiate collagenase (potentiate melting)
- delay vascularization (vessels help with healing)
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Signs of ulcerative keratitis. (8)
- lacrimation
- blepharospasm (pain)
- blepharedema
- Photophobia (pain)
- conjunctival hyperemia/ chemosis
- corneal edema
- miosis
- aqueous flare
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Causes of equine corneal ulcers. (7)
- trauma
- foreign body
- eosinophilic keratitis
- equine herpesvirus-2
- immune-mediated
- indolent ulcer
- exposure keratitis
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Describe the use of antibiotics in treatment of equine corneal ulcers. (4 principals)
- broad-spectrum antibiotics that DO NOT penetrate intact epithelium: Neo-poly-bac- triple antibiotic, Oxytet-polyB- terrmycin, anti-collagenase, promotes epithelialization
- broad-spectrum antibiotics that DO penetrate intact epithelium: chloramphenicol, fluoroquiniolones- cipro, levoflox, ofolx
- Given every 2-6hours
- Gentamicin is a poor choice!!!!!!
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Describe the use of atropine in treating equine corneal ulcers.
as needed to dilate the pupil, but NOT more than 2x a day (can induce ileus and colic)
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Why is it important to treat pain associated with corneal ulcers, and what do we use?
- a horse with a painful eye is going to be more difficult to treat
- use systemic NSAIDs- flunixine, firocoxib, bute
- maybe topical NSAIDs- diclofenac
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How do we achieve anti-collagenase therapy? (3)
- equine serum
- topical tetracycline
- systemic doxycycline
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When is surgery indicated for treatment of corneal ulcers? (3)
- refractory to medical therapy
- progressive depth and/ or diameter
- deep or perforated ulcers
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When is a corneal ulcer classified as "complicated"? (6)
- slow to heal
- stromal loss/ collagenase activity
- secondary infection
- corneal vascularization
- worsening despite treatment
- caused by severe trauma
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Describe superficial corneal ulcers. (3)
- typically very painful
- heal within 3-7 days if cause is removed
- fluoroscein positive
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Describe the routine treatment of superficial corneal ulcers. (4)
- broad spectrum topical antibiotics every 6 hours (neo-poly-bac or oxytet-polyB)
- atropine every 12-72 hours
- systemic NSAIDs
- recheck in 3-5 days
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How do you handle a superficial ulcer that is complicated/ not healing? (3)
- look for inciting cause
- culture/ susceptibility
- alter therapy accordingly
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What are signs of corneal infection? (7)
- cellular infiltrate
- marked hyperemia/ chemosis
- increased pain
- anterior uveitis (miosis, flare, hypopyon)
- progressive edema, size, and/ or depth (collagenase)
- corneal vascularization
- non-responsive to medical therapy
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When is healing expected with an infected superficial corneal ulcer?
14-21 days
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Describe mid-stromal corneal ulcers. (5)
- can see depth/ "crater" (this indicated collagenase activity)
- fluoroscein positive
- usually associated with infection--> always do cytology and culture!
- increased corneal edema
- increased instances of uveitis
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Describe medical management of stromal ulcers. (3)
- initial therapy same as superficial ulcer (if <50% depth)
- fluoroquinolones if refractory
- tetracycline and/ or serum for anti-collagenase
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How long does it take stromal ulcers to heal?
2-8 weeks
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Surgery is indicated for stromal ulcers if...
- ulcer >50% depth
- progressive depth or size, even with medical management
- --> keratectomy and conj graft
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What organisms are usually implicated in melting corneal ulcers? (2)
- Pseudomonas aeruginosa
- beta-hemolytic strep
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What diagnostics are imperative with melting corneal ulcers? (2)
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What is the treatment for melting corneal ulcers? (6)
- topical antibiotics every 2-4 hours (fluoroquinolones)
- autogenous serum every 2-4 hours
- tetracycline topical every 4-8 hours
- oral doxycycline every 12-24 hours
- [choose one anti-collagenase therapy]
- surgery usually indicated- debride melting portion, conj graft
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Describe the clinical appearance of a desmetocele. (3)
- stromal edema with a crater in the cornea- clear descemets membrane
- donut fluoroscein stain (descemets membrane does not stain, but surrounding stroma does)
- EMERGENCY- perforation is imminent
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How is a desmetocele treated? (3)
- emergency surgery- conj graft, corneoscleral transposition, corneal transplant
- topical antibiotics only
- systemic NSAIDs
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Describe the clinical appearance of a ruptured corneal ulcer. (5)
- deep defect surrounding a protruding area of clotted aqueous or uveal prolapse
- shallow anterior chamber
- dyscoria
- visible leaking aqueous
- siedel test (fluroscein stain on eye- either enters the anterior chamber or can see aqueous leaking in stained area)
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What are factors of poor prognosis with corneal perforation/ laceration? (6)
- blunt trauma
- significant hyphema
- laceration >15mm
- lens is perforated
- if a large uveal prolapse through the incision is present
- no consenual PLR or dazzle
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** __________ lacerations have better prognosis than ___________ lacerations due to... (2)
- Axial; limbal
- less daage to uvea and further distance from lens.
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When is US required with corneal laceration?
if vitreous and retina cannot be visualized
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Consider enucleation with corneal laceration if... (3)
- no consensual PLR
- large uveal prolapse present
- US shows significant blood in vitreous or retinal detachment
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What are risk factors for fungal keratitis? (4)
- chronic corneal ulcers
- topical corticosteroid use
- dirty environment
- more common in summer months (humidity)
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What is the clinical appearance with fungal keratitis? (2)
- multifocal areas of cellular infiltrate and colonies of fungal organisms- white lesions, deep in corneal stroma
- usually severe pain and uveitis
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Describe the treatment of fungal keratitis. (4)
- topical antifungals- natamycin (not used much b/c suspension, expensive)
- imidazole antibiotics- miconazole (only if ulcerative), itraconazole (with DMSO), voriconazole (topical); voriconazole penetrates intact epithelium (best option); fluconazole orally (if abscess)
- +/- surgical debridement
- +/- conj graft
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How does corneal stromal abscess occur?
- superficial corneal ulcer allows opportunistic infection
- ulcer heals, trapping microorganism inside the stroma
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How do corneal stromal abscesses appear clinically? (6)
- yellow-white corneal stromal infiltrate
- corneal edema
- deep corneal vascularization
- pain
- anterior uveitis
- negative fluoroscein
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What topical antibiotic is used for corneal stromal abscessation?
ciprofloxacin (flurorquinolones are the only antibiotic that penetrate intact epithelium)
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What topical antifungal can penetrate intact corneal epithelium to treat a stromal abscess?
voriconazole
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Describe the treatment of corneal stromal abscessation. (5)
- fluoroquinolone or chloramphenicol topically
- manage secondary uveitis
- topical or oral antifungals (voriconazole topical)
- keratctomy
- conj graft
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What 2 fungi are most common implicated in corneal abscesses?
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What are signs of indolent ulcers? (7)
- superficial
- mildly painful or non-painful
- loose or redundant epithelium borders
- no cellular infiltrate
- slow to vascularize
- middle-aged to older horses
- metabolic syndrome
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Describe indolent ulcer management. (4)
- rule out infection!!!! with culture and cytology
- debride loose epithelium
- diamond burr debridement preferred (can do grid keratotomy)
- oxytet topically
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Describe eosinophilic keratitis. (5)
- eosinophilic infiltration of the cornea
- ulcerative or non-ulcerative
- vessels coming from limbus
- pink to white infiltrate in the cornea
- most common in summer months
- diagnosed by clinical signs and cytology
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What are clinical signs of eosinophilic keratitis? (4)
- conj hyperemia
- peripheral corneal vascularization and caseous infiltrate (white, pink, yellow)
- +/- blepharospasm
- +/- ulceration
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What is the treatment for eosinophilic keratitis? (2)
- routine ulcer therapy if ulcer
- topical alomide (mast cell stabilizer)- takes 3-4 weeks of treatment, may take months to resolve
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Describe immune-mediated keratitis. (6 principals)
- typically non-painful
- usually non-ulcerative
- corneal vascularization
- white to yellow stromal infiltrate
- slowly progressive
- epithelial, stromal and endothelial forms- characterized by depth of cornea that it affects
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How is immune-mediated keratitis diagnosed?
- diagnosis of exclusion
- rule out bacterial and fungal keratitis
- rule out EHV-2 with anti-viral treatment
- rule out atypical invasive corneal SCC
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How is immune-kediated keratitis managed?
- many options- different horses respond to different immunomodulatory drugs
- topical cyclosporine or tacrolimus
- topical corticosteroid (rule out infection and ulcer first!)
- oral doxycycline
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What are causes of corneal infiltrates? (4)
- infectious
- scar/ fibrosis
- cellular- neoplasia, inflammatory
- non-cellular- mineral/ calcium, lipid
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