Cornea

Question 1

Differences between epithelium and endothelium in: a) # of cell layers, b) mitosis and healing, c) corneal edema that results

Answer 1

Epithelium:
a) 8-15 layers
b) Process: retraction of epithelial cells at margin of injury–> cells become thicker–> PMNs from tear film arrive–> ameboid movement of monolayer of epithelial cells to cover defect–> mitosis of basal cells to reestablish thickness(24-48 hours)
-full thickness mitosis occurs every 7 days
-ulcers heal in 48-72 hours
c) focal edema at site of ulcer
Endothelium
a) 1 layer hexagonal cells
b) no mitosis; heals by cellular enlargement (hypertrophy) and migration
c) diffuse edema

Question 2

How does the cornea maintain deturgescence? What is the role of carbonic anhydrase?

Answer 2

1. Evaporation of tears– tears are hypertonic and draw fluid from the corneal stoma
2. Epithelium as mechanical barrier
3. Endothelium as mechanical barrier and metabolic pump (Na+K+ATPase)
   CA enzyme supplied the bicarbonate ion necessary for Na+ cotransport into the aqueous humor

Question 3

What are the properties of the cornea that allow it to remain transparent?

Answer 3

1. Smoothness of epithelium aided by tear film
2. Orderly arrangement + small size of stromal collagen due to glycosaminoglycans
3. Absence of blood vessels and pigments
4. Deturgescence of the cornea

Question 4

How long after injury does it take for corneal epithelial injury to heal?

Answer 4

48-72 hours

Question 5

Which corneal ulcers are more painful: superficial or deep? Which of these is fluorescein negative?

Answer 5

Superficial ulcers are more painful. Deep ulcers are fluorescein negative

Question 6

Which corneal ulcers are more painful: superficial or deep? Which of these is fluorescein negative?

Answer 6

Superficial ulcers are more painful. Deep ulcers are fluorescein negative

Question 7

3 categories of drugs used to treat corneal ulcers and reasons for their uses

Answer 7

1. Antibiotics- 4th generation fluoroquinolones (Midstromal, melting ulcers), Tetracyclines (indolent ulcers)
   2.Anticollagenase- Tetracyclines
   3.Antivirals- active viral infections in cats (i.e. herpes flare-ups)
   4? Artificial tear ointments
   5? Atropine- relax pupil muscles

Question 8

What category of drugs is contraindicated in corneal ulcer management?

Answer 8

Corticosteroids

Question 9

a) Difference between third-eyelid flap and conjunctival flap? b) Which provides vascularization to the wound? c) Which is better in a patient with a desmetocele?

Answer 9

a)
- corneal/corneal-conjunctival flaps provide blood vessels, fibroblasts, collagen, and macrophages to promote healing
- third-eyelid flaps only prevent outside trauma to the eye but don’t proactively heal ulcers
b) corneal-conjunctival flaps
c) corneal-conjunctival

Question 10

Eosinophilic keratitis

a) species/breed predispositions
b) 2 criteria for diagnosis
c) management

Answer 10

a) cats
b) eosinophils and/or mast cells on cytology
c) Topical corticosteroids (0.1% dexamethasone) or Megesterol acetate (Ovaban). Topical&raquo_space; oral

Question 11

Corneal sequestration

a) species/breed predispositions
b) 2 criteria for diagnosis
c) management

Answer 11

a) cats– brachycephalic breeds (Persians and Himalayans)
b) brown-black, painful, fluorescein negative
c) Superficial keratectomy (+/- conjunctival graft, corneal transplant), topical antibiotics, atropine, and artificial tears post-surgery

Question 12

Chronic Superficial Keratitis (Pannus)

a) species/breed predispositions
b) 2 criteria for diagnosis
c) management

Answer 12

a) German Shepherds (pure bred and mix), Greyhounds, dogs exposed to a lot of UV radiation
b) lymphocytes + plasma cells on cytology, lateral cornea (inferior-temporal limbus), non-painful, vascularized
c) topical corticosteroids (0.1% dexamethasone), topical immunosuppressive (cyclosporin, tacrolimus)

Question 13

What is an indolent ulcer and how do you treat it?

Answer 13

• chronic superficial ulcer resulting from failure of attachment of epithelium to the underlying basement membrane
• loose/redundant epithelial borders
• non/mildly painful
• Boxers and middle aged-to-older dogs predisposed
• Debridement of redundant epithelium–> grid keratectomy–> (+/- contact lens)–> may need to repeat debridement and keratectomy multiple times, + topical Tetracycline

Question 14

Corneal dystrophy

a) what is it?
b) clinical appearance
c) predisposed breeds of dogs
d) treatment

Answer 14

a) 1º non-cellular corneal infiltrates composed of crystalline materials (cholesterol, minerals)
b) non-painful, non-vascularized, often bilateral, birefringent
c) dogs; looks different between breeds: airedale, alaskan malamute, beagle, boston terrier, chihuahua, american cocker spaniel, dachshund, collie, samoyed, shetland sheepdog, siberian husky
d) no treatment necessary

Question 15

Corneal degeneration

a) what is it?
b) what causes it?

Answer 15

a) 2º non-cellular corneal infiltrates composed of crystalline materials
b)
- Previous corneal inflammation– ex. dog treated for NGEK
- Systemic diseases: Hypothyroidism, Hypercholesterolemia of Cushing’s, Hypercalcemia, Diabetes Mellitus, chronic topical or systemic corticosteroids
c) no ocular treatment necessary

Question 16

Dermoid (Choristoma)

a) what is it?
b) treatment
c) breeds affected

Answer 16

a)
- normal dermal epithelium (usually haired) on the cornea
- congenital
- usually at temporal limbus +/- involvement of conjunctiva and eyelids
b) Superficial keratectomy–ONLY if bothering patient, not for cosmesis
c) dachshund, doberman, dalmatian, german shepherd, saint bernard

Question 17

5 causes of corneal lesion that does not retain fluorescein

Answer 17

Non-staining lesions usually the result of diffuse edema caused by endothelial damage

1. anterior uveitis (decreased pressure in eye; ex. dog with blastomycosis)
2. glaucoma
3. trauma
4. endothelial dystrophy– breed related (chihuahuas, boston terriers)
5. anterior lens luxation