Disorders of the Cornea Flashcards
What contributes to the cornea being clear?
-the absence of blood vessels
-a very intricate organization of collagen that is arranged perfectly for light to pass through
What is the role of descemets membrane?
To dehydrate the cornea through the action of the endothelium
What are some causes of corneal edema?
Dysfunction of the endothelial layer (due to uveitis, glaucoma, etc) or loss of the epithelium (ulcers)
What are the main etiologies behind ulcerative keratitis?
Trauma, foreign body, exposure/paralytic keratitis, EHV (uncommon to rare), KCS (rare)
Describe the normal progression of corneal ulcers
-when epithelium is lost, the adjacent epithelium within a few days will close the stromal defect
-superficial ulcers can heal without intervention
-when stroma is exposed, bacteria can quickly invade and worsen ulcers
What are the categories of corneal ulcers?
Superficial
Stromal- stroma is affected, the whole ulcer appears cloudy
Descemetocele- will see a clear area in the middle of regional cloudiness as the Descemet’s membrane is exposed which doesn’t hold fluid
What diagnostics are indicated for corneal ulcers?
-most importantly, do a full exam in order to try and determine the underlying cause (should do every time if you suspect an ulcer)
-also should consider culture, cytology, or fluorescein stain but these aren’t necessary in every case
When is cytology the most helpful as a diagnosis in horse Opthalmic cases?
In the case of fungal infections, melting ulcers
When do ulcers become complicated?
-when there is secondary infection with either bacteria or fungi, stromal degradation, or iridocyclitis (uveitis)
What causes the melting appearance in a melting ulcer?
Stromal collagen that has been liquified (degraded) due to enzymes from bacteria/fungi or from the bodies immune response
-often uveitis occurs in these cases resulting in diffuse edema
What is unique about the appearance of an eye with a fungal infection?
-there is a “moat” surrounding the ulcer
What are the goals of therapy with ulcer cases?
- Controlling corneal infection
- Inhibiting corneal proteolysis
- Managing secondary uveitis
- Increasing patient comfort
What is the best way to apply topical solutions to the eye of a horse?
Topical lavage system -expensive but well worth it
How long should topical antimicrobials be used in ulcer cases?
Until healed- eyes do not take up fluorescein stain
-frequency is dictated by severity of ulcers (3 times a day minimum in most cases)
-Triple antibiotic is a good broad spectrum option
What are the unique considerations when using topical antifungals in the eyes of equine patients?
-usually have to use compounded ophthalmic medications
-some people use dermatologic preparations, but be aware of risks (label says not to put in eye)
Why should you use cycloplegics in ulcer cases?
Ulcers are very painful and cause ciliary spasm, which can worsen them
-cycloplegics prevent the spasming
-the main one used is topical atropine, helps to prevent reflex uveitis
What other medications can be added on in the case of ulcers?
-systemic NSAIDs
-antiproteases (topical autologous serum, topical N acetylcysteine, topical or systemic tetracyclines, oral doxycycline/minocycline)- indicated if ulcer starts to appear melting
What are the options for surgical management of ulcer cases?
Indications: deep ulcers or fungal infections
Procedures: stromal antimicrobial injections, keratectomy, conjunctival flap, others
What causes corneal perforations?
-untreated ulcers leading to globe ruptures
-sharp lacerations
-blunt trauma
Clinical findings include iris/fibrin prolapse, corneal edema, hyphemia/hypopyon
Where does the cornea usually rupture in the case of blunt trauma?
At the corneal-scleral junction
-stress riser region
These eyes need to be enucleated, compared to those with sharp lacerations which may have a good prognosis with surgical correction
What worsens the prognosis in cases of corneal perforation?
Blunt trauma, ulcerative etiology, endophthalmitis, severe hyphema, lens rupture, chronic rupture
T/F: A corneal perforation is always a surgical disease
True
-preoperative management: topical ulcer meds and oral NSAIDs
What typical clinical findings do you see in corneal abscess cases?
-Yellow-white stromal opacity
-severe ocular discomfort
-secondary uveitis
*can be either septic or non-septic, but there is no way to practically sample them
How can corneal abscesses be managed?
Medical: similar to ulcers, antimicrobials must be able to penetrate the epithelium (floroquinolones are the best option) manage secondary uveitis (often what kills the eye in these cases), must vascularize to resolve (may not vascularize if too deep)
-avoid topical steroids- will only resolve signs transiently
Surgery: more often indicated over medical
-quicker resolution than medical approach
-involves surgical excision and a conjunctival flap and keratoplasty procedures
