Disorders of the Cornea

Question 1

T/F: the corneal epithelium is hydrophilic

Answer 1

false – hydrophobic

Question 2

T/F: the cornea should be clear

Answer 2

true – there are no blood vessels and the tissue is arranged in a manner so that light can freely pass through.

Question 3

what is the function of the corneal endothelium?

Answer 3

dehydrate the cornea

Question 4

what are the 5 potential etiologies of ulcerative keratitis?

Answer 4

1. trauma
2. foreign body
3. exposure/paralytic keratitis
4. equine herpes virus (uncommon)
5. KCS (very rare)

Question 5

what contributes to the progression of a complicated corneal ulcer?

Answer 5

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.

Question 6

what are the 3 categories of corneal ulcers?

Answer 6

1. superficial
2. stromal (superficial, mid, or deep-stromal)
3. desmetocoele

Question 7

what is the MOST important diagnostic among the few you can do to diagnose a corneal ulcer?

Answer 7

Look for an underlying cause!!!

other diagnostics that are indicated sometimes: stain the eye (to confirm presence), cytology, culture

Question 8

T/F: An eyelid block is not required for diagnosing a corneal ulcer

Answer 8

false – its required because you need to investigate the cause of the ulcer and the horse isnt going to hold the eye open.

Question 9

what is the MOST common cause of complicated corneal ulcers?

Answer 9

Secondary infection (bacterial or fungal)

remember: the bacteria dont cause the ulcer, they invade afterwards and make things worse.

Question 10

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?

Answer 10

lytic corneal stromal collagen.
This is indicative of a melting ulcer. The corneal stroma gets degraded by organisms or inflammatory cells.

Question 11

What clinical finding is indicative of keratomycosis (fungal infection)?

Answer 11

A clear zone at the periphery of a deep stromal ulcer.

Question 12

What are the 4 goals of therapy for corneal ulcers?

Answer 12

1. control or prevent corneal infection (through use of antibiotics)
2. inhibit corneal proteolysis (melting)
3. manage any secondary uveitis
4. increase patient comfort

Question 13

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?

Answer 13

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.

Question 14

What can you prescribe a horse with ulcerative keratitis for pain?

Answer 14

1. Topical atropine (cycloplegic agent)
2. systemic NSAIDs

Question 15

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?

Answer 15

1. topical autologous serum
2. topical N-acetylcysteine
3. topical or systemic tetracyclines (doxy or mino)

Question 16

What are indications for surgical management of ulcerative keratitis in horses?

Answer 16

1. deep ulcers
2. fungal ulcers

Question 17

T/F: desmetoceles can be managed medically

Answer 17

false – they require surgical treatment.

Question 18

what are the 3 most common etiologies of corneal perforations?

Answer 18

1. chronic ulcers that rupture
2. sharp lacerations
3. blunt trauma

Question 19

what are typical clinical findings of corneal perforations?

Answer 19

• iris prolapse/fibrin
• corneal edema
• hyphema/hypopyon

in blunt trauma cases, the rupture typically occurs at the corneal-scleral junction/limbus

Question 20

T/F: you can medically manage a corneal perforation

Answer 20

false – corneal perforations are ALWAYS q surgical disease.
Pre-operatively, you can give them topical + systemic antibiotics, topical antifungals, topical atropine, and oral NSAIDs.

Question 21

What factors may worsen the prognosis of a corneal perforation?

Answer 21

1. if blunt trauma was the cause
2. if chronic ulceration was the cause
3. endophthalmitis
4. severe hyphema
5. hyphema
6. chronic rupture
7. lens ruptures

Question 22

T/F: a corneal perforation caused by a sharp laceration has a better prognosis than if caused by blunt trauma.

Answer 22

true

Question 23

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?

Answer 23

corneal abscess

Question 24

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?

Answer 24

flouroquinolones for epithelial and stomal penetration.

Question 25

T/F: during the treatment of a corneal abscess, the cornea must vascularize in order to resolve.

Answer 25

true this can create moderate scarring.

Question 26

T/F: surgical excision is not indicated for corneal abscesses

Answer 26

false -- this treatment method is a much quicker resolution than the medical approach. It involves surgical excising the lesion and placing a conjunctival flap.

Question 27

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

Answer 27

band keratopathy commonly seen in horses with ERU.

Question 28

What is the biggest distinguishing characteristic about immune-mediated keratitis (IMMK)?

Answer 28

it is usually NON-painful

Question 29

What is the cause of IMMK?

Answer 29

uncertain but the inciting event causes a loss of corneal immune privilege, then localization of antigen-presenting cells and lymphocytes propagates the disease.

Question 30

what are the 4 clinical classifications of IMMK?

Answer 30

1. epithelial 2. superficial stromal 3. mid-stromal 4. endothelial

Question 31

Describe the appearance of epithelial IMMK

Answer 31

multifocal punctate to coalescing non-ulcerated opacities with NO vascularization and no/minimal discomfort. (looks like an eye with polka dots)

Question 32

Describe the appearance of superficial stromal IMMK

Answer 32

stromal haze vascularization cellular infiltrate (slight green/yellow appearance) no/minimal discomfort

Question 33

Describe the appearance of mid-stromal IMMK

Answer 33

stromal haze vascularization larger cellular infiltrate (green/yellow appearance) no/very mild discomfort

Question 34

What differentiates a case of mid-stromal IMMK from a corneal abscess?

Answer 34

corneal abscesses are very painful, IMMK is not.

Question 35

Describe the appearance of endothelial IMMK

Answer 35

severe regional or diffuse corneal edema this form of IMMK does NOT respond to any treatments.

Question 36

How can you medically treat IMMK?

Answer 36

Topical steroids and/or cyclosporine LIFELONG remember, nothing is effective in treating endothelial IMMK.

Question 37

What is involved in surgical treatment of IMMK?

Answer 37

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

Question 38

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?

Answer 38

eosinophilic keratoconjunctivitis perform corneal cytology to see eosinophils

Question 39

what is the etiology of eosinophilic keratoconjunctivitis?

Answer 39

unknown but thought to be immune-mediated or an allergy/hypersensitivity

Question 40

How do you treat a patient with eosinophilic keratoconjunctivitis?

Answer 40

1. topical + systemic corticosteroids 2. topical cyclosporine 3. systemic antihistamines 4. if ulcer, keratectomy

Question 41

what is the prognosis for eosinophilic keratoconjunctivitis?

Answer 41

good.

Question 42

T/F: corneoconjunctival SCC in horses typically appears at the medial limbus

Answer 42

false -- lateral limbus. it is typically raised and fleshy/verrucous in appearance.

Question 43

What are the various treatment options for corneoconjunctival SCC?

Answer 43

1. surgical excision 2. CO2 laser ablation 3. cryotherapy (adj) 4. photodynamic therapy 5. radiation therapy (adj) 6. topical chemo

Question 44

what is the prognosis for corneoconjunctival SCC?

Answer 44

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.