Disorders of the Cornea

Question 1

What contributes to the cornea being clear?

Answer 1

-the absence of blood vessels
-a very intricate organization of collagen that is arranged perfectly for light to pass through

Question 2

What is the role of descemets membrane?

Answer 2

To dehydrate the cornea through the action of the endothelium

Question 3

What are some causes of corneal edema?

Answer 3

Dysfunction of the endothelial layer (due to uveitis, glaucoma, etc) or loss of the epithelium (ulcers)

Question 4

What are the main etiologies behind ulcerative keratitis?

Answer 4

Trauma, foreign body, exposure/paralytic keratitis, EHV (uncommon to rare), KCS (rare)

Question 5

Describe the normal progression of corneal ulcers

Answer 5

-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

Question 6

What are the categories of corneal ulcers?

Answer 6

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

Question 7

What diagnostics are indicated for corneal ulcers?

Answer 7

-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

Question 8

When is cytology the most helpful as a diagnosis in horse Opthalmic cases?

Answer 8

In the case of fungal infections, melting ulcers

Question 9

When do ulcers become complicated?

Answer 9

-when there is secondary infection with either bacteria or fungi, stromal degradation, or iridocyclitis (uveitis)

Question 10

What causes the melting appearance in a melting ulcer?

Answer 10

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

Question 11

What is unique about the appearance of an eye with a fungal infection?

Answer 11

-there is a “moat” surrounding the ulcer

Question 12

What are the goals of therapy with ulcer cases?

Answer 12

1. Controlling corneal infection
2. Inhibiting corneal proteolysis
3. Managing secondary uveitis
4. Increasing patient comfort

Question 13

What is the best way to apply topical solutions to the eye of a horse?

Answer 13

Topical lavage system -expensive but well worth it

Question 14

How long should topical antimicrobials be used in ulcer cases?

Answer 14

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

Question 15

What are the unique considerations when using topical antifungals in the eyes of equine patients?

Answer 15

-usually have to use compounded ophthalmic medications
-some people use dermatologic preparations, but be aware of risks (label says not to put in eye)

Question 16

Why should you use cycloplegics in ulcer cases?

Answer 16

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

Question 17

What other medications can be added on in the case of ulcers?

Answer 17

-systemic NSAIDs
-antiproteases (topical autologous serum, topical N acetylcysteine, topical or systemic tetracyclines, oral doxycycline/minocycline)- indicated if ulcer starts to appear melting

Question 18

What are the options for surgical management of ulcer cases?

Answer 18

Indications: deep ulcers or fungal infections

Procedures: stromal antimicrobial injections, keratectomy, conjunctival flap, others

Question 19

What causes corneal perforations?

Answer 19

-untreated ulcers leading to globe ruptures
-sharp lacerations
-blunt trauma

Clinical findings include iris/fibrin prolapse, corneal edema, hyphemia/hypopyon

Question 20

Where does the cornea usually rupture in the case of blunt trauma?

Answer 20

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

Question 21

What worsens the prognosis in cases of corneal perforation?

Answer 21

Blunt trauma, ulcerative etiology, endophthalmitis, severe hyphema, lens rupture, chronic rupture

Question 21

T/F: A corneal perforation is always a surgical disease

Answer 21

True
-preoperative management: topical ulcer meds and oral NSAIDs

Question 22

What typical clinical findings do you see in corneal abscess cases?

Answer 22

-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

Question 23

How can corneal abscesses be managed?

Answer 23

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

Question 24

What is band keratopathy?

Answer 24

Seen mostly in horses that have been suffering from equine recurrent uveitis
-involves a band of corneal mineralization/calcification
-typically this is non painful unless ulceration occurs due to sloughing material

Can in some cases use surgical debridement and EDTA treatment

Question 25

Describe the clinical features of immune mediated keratitis

Answer 25

-chronic, non-painful or minimally painful condition that is most commonly unilateral
-etiopathogenesis is uncertain: inciting event causes loss of corneal immune privilege
-localization of antigen-presenting cells and lymphocytes then propagate the disease
-4 clinical classification, but management varies from case to case

Question 26

Describe the appearance of epithelial IMMK, stromal IMMK

Answer 26

Epithelial: Multifocal punctate to coalescing non ulcerated epithelial opacities over the cornea
Stromal: stromal haze, vascularization and cellular infiltrates (usually slightly green/yellow in appearance)
Mid stromal: more severe version of the stromal form
Endothelial: diffuse corneal edema

Question 27

What are the main medications used for equine IMMK?

Answer 27

Medical: topical steroids and/or cyclosporine (lifelong trt), though not effective for endothelial form (consider topical bromfenac in these cases, but not great efficacy)

Question 28

What is the main surgical option in IMMK cases?

Answer 28

-cyclosporin implants (1 year duration)
-lesion excision for the stromal forms of the disease may also be curative
-consider adding on photodynamic therapy

Question 29

Describe eosinophilic keratoconjunctivitis

Answer 29

-clinical findings include ocular discomfort, raised pink-white necrotic corneal plaques, variable corneal ulceration
-etiology is unknown, but may be immune mediated or allergy/hypersensitivity
-diagnose via corneal cytology (will see eosinophils)
-treatment: topical/systemic corticosteroids (only time to use topically is in this case), topical cyclosporine, systemic antihistamines, keratectomy
-prognosis: generally good, but can recur over time (better with long term antihistamines)

Question 30

Describe corneoconjunctival SCC

Answer 30

-horses with UV exposure, light skin, and maybe exposure to certain viruses may be more at risk
-appears as a raised, proliferative pink mass typically on lateral aspect of cornea
-treat with surgical excision and adjunct therapy (cryo, CO2 laser, radiation, photodynamic therapy), and topical chemo
-prognosis good with appropriate surgical management and other therapies, metastasis is rare