Disorders of the Cornea Flashcards
T/F: the corneal epithelium is hydrophilic
false – hydrophobic
T/F: the cornea should be clear
true – there are no blood vessels and the tissue is arranged in a manner so that light can freely pass through.
what is the function of the corneal endothelium?
dehydrate the cornea
what are the 5 potential etiologies of ulcerative keratitis?
- trauma
- foreign body
- exposure/paralytic keratitis
- equine herpes virus (uncommon)
- KCS (very rare)
what contributes to the progression of a complicated corneal ulcer?
In normal corneal healing, the epithelial cells undergo mitosis and heal within 3-5 days.
However, if bacteria gain entry into the epithelial defect, this can lead to further tissue destruction and healing becomes unachievable.
what are the 3 categories of corneal ulcers?
- superficial
- stromal (superficial, mid, or deep-stromal)
- desmetocoele
what is the MOST important diagnostic among the few you can do to diagnose a corneal ulcer?
Look for an underlying cause!!!
other diagnostics that are indicated sometimes: stain the eye (to confirm presence), cytology, culture
T/F: An eyelid block is not required for diagnosing a corneal ulcer
false – its required because you need to investigate the cause of the ulcer and the horse isnt going to hold the eye open.
what is the MOST common cause of complicated corneal ulcers?
Secondary infection (bacterial or fungal)
remember: the bacteria dont cause the ulcer, they invade afterwards and make things worse.
If you are examining a horse with a corneal ulcer and you swab some white gooey material off of the cornea, what is this material most likely?
lytic corneal stromal collagen.
This is indicative of a melting ulcer. The corneal stroma gets degraded by organisms or inflammatory cells.
What clinical finding is indicative of keratomycosis (fungal infection)?
A clear zone at the periphery of a deep stromal ulcer.
What are the 4 goals of therapy for corneal ulcers?
- control or prevent corneal infection (through use of antibiotics)
- inhibit corneal proteolysis (melting)
- manage any secondary uveitis
- increase patient comfort
If you were prescribing a patient with a corneal ulcer topical antibiotics or antifungals, what would be your recommendations for how often/long they should administer them?
UNTIL HEALED (you’ll need to stain the eye to check for healing)
usually they are administered TID, but it will depend on the severity of the ulcer present.
What can you prescribe a horse with ulcerative keratitis for pain?
- Topical atropine (cycloplegic agent)
- systemic NSAIDs
What are a few anti-proteases that you may be inclined to prescribe for a horse with ulcerative keratitis and there is concern for progression towards melting ulcer?
- topical autologous serum
- topical N-acetylcysteine
- topical or systemic tetracyclines (doxy or mino)
What are indications for surgical management of ulcerative keratitis in horses?
- deep ulcers
- fungal ulcers
T/F: desmetoceles can be managed medically
false – they require surgical treatment.
what are the 3 most common etiologies of corneal perforations?
- chronic ulcers that rupture
- sharp lacerations
- blunt trauma
what are typical clinical findings of corneal perforations?
- iris prolapse/fibrin
- corneal edema
- hyphema/hypopyon
in blunt trauma cases, the rupture typically occurs at the corneal-scleral junction/limbus
T/F: you can medically manage a corneal perforation
false – corneal perforations are ALWAYS q surgical disease.
Pre-operatively, you can give them topical + systemic antibiotics, topical antifungals, topical atropine, and oral NSAIDs.
What factors may worsen the prognosis of a corneal perforation?
- if blunt trauma was the cause
- if chronic ulceration was the cause
- endophthalmitis
- severe hyphema
- hyphema
- chronic rupture
- lens ruptures
T/F: a corneal perforation caused by a sharp laceration has a better prognosis than if caused by blunt trauma.
true
A horse presents to you and has a yellow-white stromal opacity in the ventral area of the cornea. On examination, this eye is very painful and you see evidence of reflex uveitis (corneal vascularization, corneal edema, etc.).
What is MOST likely the diagnosis?
corneal abscess
You have just diagnosed your patient with a corneal abscess and you wish to treat them with antimicrobials. Which drug class is BEST to use?
flouroquinolones for epithelial and stomal penetration.
T/F: during the treatment of a corneal abscess, the cornea must vascularize in order to resolve.
true
this can create moderate scarring.
T/F: surgical excision is not indicated for corneal abscesses
false – this treatment method is a much quicker resolution than the medical approach.
It involves surgical excising the lesion and placing a conjunctival flap.
Name the following condition:
a degenerative condition that is often associated with chronic uveitis. typically non-painful unless ulcers are present. characterized by corneal mineralization/calcification
band keratopathy
commonly seen in horses with ERU.
What is the biggest distinguishing characteristic about immune-mediated keratitis (IMMK)?
it is usually NON-painful
What is the cause of IMMK?
uncertain but the inciting event causes a loss of corneal immune privilege, then localization of antigen-presenting cells and lymphocytes propagates the disease.
what are the 4 clinical classifications of IMMK?
- epithelial
- superficial stromal
- mid-stromal
- endothelial
Describe the appearance of epithelial IMMK
multifocal punctate to coalescing non-ulcerated opacities with NO vascularization and no/minimal discomfort.
(looks like an eye with polka dots)
Describe the appearance of superficial stromal IMMK
stromal haze
vascularization
cellular infiltrate (slight green/yellow appearance)
no/minimal discomfort
Describe the appearance of mid-stromal IMMK
stromal haze
vascularization
larger cellular infiltrate (green/yellow appearance)
no/very mild discomfort
What differentiates a case of mid-stromal IMMK from a corneal abscess?
corneal abscesses are very painful, IMMK is not.
Describe the appearance of endothelial IMMK
severe regional or diffuse corneal edema
this form of IMMK does NOT respond to any treatments.
How can you medically treat IMMK?
Topical steroids and/or cyclosporine LIFELONG
remember, nothing is effective in treating endothelial IMMK.
What is involved in surgical treatment of IMMK?
lesion excision (for stromal forms this is curative)
cyclosporine implants (really only for superficial or stromal; last for 1 yr, make sure they respond to topical first)
or photodynamic therapy
You examine a very painful horse and find raised pinkish/whitish necrotic corneal plaques. You also note a corneal ulcer and caseous ocular discharge.
What is MOST likely your diagnosis and how would you proceed to confirm this diagnosis?
eosinophilic keratoconjunctivitis
perform corneal cytology to see eosinophils
what is the etiology of eosinophilic keratoconjunctivitis?
unknown but thought to be immune-mediated or an allergy/hypersensitivity
How do you treat a patient with eosinophilic keratoconjunctivitis?
- topical + systemic corticosteroids
- topical cyclosporine
- systemic antihistamines
- if ulcer, keratectomy
what is the prognosis for eosinophilic keratoconjunctivitis?
good.
T/F: corneoconjunctival SCC in horses typically appears at the medial limbus
false – lateral limbus.
it is typically raised and fleshy/verrucous in appearance.
What are the various treatment options for corneoconjunctival SCC?
- surgical excision
- CO2 laser ablation
- cryotherapy (adj)
- photodynamic therapy
- radiation therapy (adj)
- topical chemo
what is the prognosis for corneoconjunctival SCC?
good to excellent with the appropriate tx. (90% cure rate)
if tx is delayed, loss of globe is likely.
if stromal invasive form, prognosis for surgical cure is poorer.
