Diseases of the Cornea Flashcards
What are the layers of the cornea (in order)?
Epithelium, stroma, Descemet’s membrane, endothelium
What are three important characteristics of the cornea that give it a clear appearance?
Avascular, anhydrous, regular arrangement of collagen fibers
A 5 year old QH gelding presents to your clinic with a stromal ulcer. The ulcer is surrounded by white to yellow infiltrate in the stroma. What is this often indicative of?
NOTE: The infiltrate is in the cornea, NOT the AC! That would be considered hypopyon.
Infection (complicated ulcer)
What would you call the irregular arrangement of collagen lamellae following injury that creates a white to grey color on the cornea?
Fibrosis
What would vascularization of the cornea tell you?
There is an inflammatory process going on (non-specific for a cause)
What are the pathophysiological reasons for corneal edema?
Fluid leaking in from tear film or corneal blood vessels, OR ineffective pumping out of fluid by the endothelium.
How long does it take for the epithelial cell basement membrane to attach to the stroma (re-adhere)?
6 weeks
How far does the epithelium migrate per day if not infected or compromised?
0.6-1.0 mm/day
What type of drug can blunt vascular ingrowth?
systemic NSAIDs
What layer of the cornea has a limited capacity for regeneration (minimal to no mitosis)?
Endothelium
What are the top 2 cultures you would reach for in you suspected an infected corneal ulcer?
Aerobic and fungal
What is the only structure lost in a superficial ulcer?
Epithelium
Why would you want to start a patient with a corneal laceration on systemic abx?
To decrease the risk of endophthalmiitis
How can you check if you have properly sutured up the corneal laceration (water tight seal) during surgery?
Seidel’s test
What are the most commonly isolated bacterial agents in Equine ulcers?
Pseudomonas, streptococcus equi, staphylococcus, corynebacterium
A 6 year old TB mare presents to you with a stromal ulcer that is showing signs of infection (white to yellow corneal cellular infiltrate with melting appearance). You decide to submit a bacterial culture, all of the following are commonly isolated bacterial agents in equine ulcers EXCEPT?
A. Streptococcus equi B. Staphylococcus C. Pseudomonas D. Corynebacterium E. Klebsiella
E. Klebsiella
What are the most commonly isolated fungal organisms in Equine ulcers?
Aspergillus and Fusarium
What are two distinguishing factors between fungal ulcers and bacterial ulcers?
Fungal ulcers commonly have groove or furrow development and plaque formation. They can also have a roughened, gritty surface.
In what instances would you suspect fungal involvement in an ulcer?
Takes a long time to heal (doesn’t heal quickly), does not vascularize, the ulcer is associated with plant or other organic material, corneal cytology shows fungal hyphae, ulcer has not responded to topical abx, the associated uveitis transiently worsens after the start of antifungals, or the patient has been treated with corticosteroids.
What is the minimum amount of time a horse would need to be treated for a fungal ulcer?
4 to 6 weeks (extended medical therapy until they are no longer taking up fluorescein stain)
How would you treat a corneal ulcer medically?
Topical abx +/- topical antifungals, mydriatic, NSAIDs (typically systemic if ulcer is moderate to severe), and serum/plasma/EDTA/NAC (to stop the melting).
How would you treat a minor epithelial defect of the cornea?
Topical antibiotic and mydriatic!
How would you treat a major stromal defect of the cornea?
CULTURE/CYTOLOGY first! Disinfect, then focus treatment (topical antibiotic +/- antifungals, serum, mydriatic, and systemic NSAIDs).
Why do we add a mydriatic as part of our treatment for corneal ulcers?
Because every eye with a corneal ulcer has anterior uveitis!
What systemic NSAID works best for intraocular inflammation?
Flunixin
How long is serum good for?
about 8 days (keep refrigerated)
A 4 year old QH gelding presents to you with a superficial, simple (not infected) ulcer. How would you treat this ulcer?
Topical broad spectrum antibiotics q6-8h
Atropine q12-24h (to effect)
+/- Serum q6h
Few doses of systemic flunixin
Recheck within 3 days and if no improvement, submit culture and cytology, consider adding anti fungal, and debride (with a q-tip) if necessary.*
What are the only type of ulcers that you can debride?
Superficial, non-melting ulcers
When there is gross melting of an ulcer, how frequently would we want to use our anti-melting drugs?
Hourly!
A 6 year old TB mare presents for a corneal ulcer. There is fibrin present in the anterior chamber and you perform a Seidel’s test (to assess if full thickness), and the results are positive. What would be the appropriate initial treatment plan for this ulcer?
Culture and then conjunctival graft/flap
A 6 year old TB mare presents for a corneal ulcer. There is fibrin present in the anterior chamber and you perform a Seidel’s test (to assess if full thickness), and the results are positive. You submit a culture and take the horse to surgery. What would be your treatment plan post-operatively?
Cover all your bases!
- Topical abx q2h
- Topical antifungal q4h
- Atropine q6h
- Serum q1-2h
- Flunixin q12h
A 3 year old Fresian gelding presents to your clinic for an iris prolapse. What would be the appropriate initial treatment plan for this horse?
Culture and then surgery to replace iris, place corneal transplant, and conjunctival graft/flap.
The portion of the iris that has prolapsed may need to be amputated in some cases
A 3 year old Fresian gelding presents to your clinic for an iris prolapse. You submit a culture and take the horse to surgery. What would be your treatment plan post-operatively?
Again, cover all your bases (and more on this one)!
- Systemic antibiotics
- Topical abx q2h
- Topical antifungal q4h
- Atropine q6h
- Serum q1-2h
- Flunixin q12h
What is the benefit of a conjunctival flap?
Provides support, brings in a blood supply to aid in healing
What is the benefit of a corneal transplant?
Fills a large hole in the corneal to provide tectonic support (usually done in conjunction with conjunctival graft)
What is the benefit of a keratectomy?
Removes necrotic tissue to speed healing
What factors contribute to an ulcer becoming indolent (non-healing)?
Infection, decreased corneal sensitivity (specifically in foals), BM abnormality, metabolic abnormalities/systemic illness, and old age
What common treatment used in small animal patients do you want to avoid in LA patients with an indolent ulcer?
grid keratotomy (Do NOT do it!)
When treating an indolent ulcer, what are the appropriate steps?
Collect C&S and cytology first, after receiving results you can perform a diamond burr debridement (or chemical debridement), then place contact lens.
Perform a keratectomy with conjunctival flap if all else fails!
Under what circumstance (in what animals) are melting ulcers usually sterile?
Foals
True or false: Painful eyes are same day emergencies!
True
