Lecture Six: Cornea

- Tear film

- Epithelium

- Stroma

- Descemet's membrane

- Endothelium

What are the 5 layers of the cornea?

Maintaining clarity

What is the ultimate goal of the cornea?

- Smooth ocular surface

- Deliver oxygen and nutrients

- Remove waste

- Allow for optical transparency

- Immunology

What are the 5 functions of the tear film?

- Lipophilic

- Hydrophilic

The epithelium is (hydrophilic/lipophilic) and the stroma is (hydrophilic/lipophilic).

- 75% water, 25% collagen

- Relatively acellular (some keratocytes)

What are the components of the stroma?

Endothelium's basement membrane

Descemet's Membrane?

Active dehydration of the stroma

What is the role of the endothelium

False

T/F: the endothelium is regenerative

Cornea

What is the most densely innervated tissue in the body?

CN 5

What nerve innervates the cornea?

Superficial

On the cornea, are most of the nerve endings superficial or deep?

brachiocephalics

less nerves in who?

reflex uveitis with corneal ulceration

cycloplegic (Atropine)

axonal reflex?

treatment?

- Loss of transparency

- Change in thickness

What are the 2 over-arching categories of corneal disease?

- Precise arrangement of collagen lamellae

- Relative dehydration

- Absence of pigment, blood vessels, and keratinization of the surface epithelium

What 3 factors result in corneal transparency?

Lipid, mineral, fibrosis

white in the cornea =

Edema

blue in the cornea =

Blood vessels, hemorrhage

red in the cornea =

- Pigment

- Necrosis (sequestrum)

- Foreign body

- Neoplasia

- Dermoid

- Iris prolapse

brown in the cornea =

Cellular infiltrate

yellow in the cornea =

Corneal dystrophy

What am I describing?

- White opacities

- Bilateral, symmetrical

- Seen in purebred dogs

- Non-painful, non-progressive

- No concern

None

What is the treatment for corneal dystrophy?

Corneal degeneration

What am I describing?

- White opacities

- Unilateral or bilateral, asymmetric

- Due to ocular surface or intraocular disease

- May have systemic implications

- Often vascularized

- Can result in ulceration

- Identify ocular/systemic diseases and treat

- Consider referral

What is the treatment for corneal degeneration?

Corneal fibrosis

What am I describing?

- White opacities

- Increased and/or disorganized collagen

- Historical keratitis

- Often associated with vascularization

- Non-painful

- No treatment

None

What is the treatment for corneal fibrosis?

Descemet's striae

What am I describing?

- White opacities

- Cracks in descemet's membrane leaving scars

- Associated with glaucoma

Glaucoma

Descemet's striae is associated with what?

Keratic precipitates

What am I describing?

- White opacities

- Clumps of cells, protein, fibrin, lipid adhered to endothelium, forming a scar

- Pathognomonic for anterior uveitis

Keratic precipitates

What is pathogneumonic for anterior uveitis?

Epithelial inclusion cyst

What am I describing?

- White opacities

- Benign entrapment of epithelium within the stroma

- Non-painful, no problems

Surgical excision (refer)

What is the treatment for epithelial inclusion cysts and neoplasia?

- SCC*

- Papilloma

- Lymphoma

- also HSA

Top 3 corneal neoplasias?

Corneal edema

What am I describing?

- Blue opacities

- Can be due to an epithelial or endothelial defect

- Ulcerative keratitis* (cornea inflammation)

- Non-ulcerative keratitis

- Keratic precipitates

- Anterior lens luxation

- Glaucoma, uveitis

What are 5 causes of focal corneal edema?

- Glaucoma

- Anterior uveitis

- Endopthalmitis

- Endothelial dystrophy

- Senile endothelial degeneration

- Endothelitis

- Blue eye (CAV-1)

What are 7 causes of diffuse corneal edema?

- Boston terrier

- Chihuahua

- Dachshund

- Basset hound

What breeds are more likely to get corneal edema due to endothelial dystrophy? (4)

- Treat primary disease

- Hyperosmotic 5% NaCl ointment

- Thermakeratoplasty (rarely used)

- Keratoleptynsis

- Corneal transplant

- Endothelial transplant - coming soon

What is the treatment for corneal edema?

- Vascularization (non-specific for ocular surface or intraocular disease)

- Intrastromal hemorrhage (blood vessels already there)

What are the potential causes of red opacities?

4

1

vascularization takes ___ days to start growing, then grow ___mm per day

Ocular surface disease (KCS, indolent ulcer, etc.)

Superficial red opacities =

Deep stromal , intraocular disease (stromal abscess, uveitis, glaucoma, etc.)

Deep red opacities =

deep vessels (hedgelike)

superficial vessels (branching)

Chronic superficial keratitis (pannus)

What am I describing?

- Red opacities

- Immune-mediated

- Seen in GSDs and sighthounds

- Non-painful, progressive

- Superficial vessels, pigmentation, corneal degeneration, fibrosis

- Starts at the temporal (lateral) limbus

- Can be blinding if no tx

Lifelong immunosuppressant maintenance:

- Topical dexamethasone

- Topical cyclosporine or tacrolimus

What is the treatment for chronic superficial keratitis (pannus)?

Eosinophilic keratitis

What am I describing?

- Red opacities

- Feline, equine, rabbit

- Implications with herpesvirus

- Recurrent, persistent

- Raised pink/white plaques from the limbus with vessels

- Usually unilateral and not ulcerative

- Variable pain

Cytology —> eosinophils, mast cells

How is eosinophilic keratitis diagnosed?

Lifelong immunomodulatory maintenance:

- Topical cyclosporine or tacrolimus

- Topical megestrol

- topical dex (if no ulcer)

What is the treatment for eosinophilic keratitis?

Pigment keratopathy

What am I describing?

- Brown opacities

- Seen in 80% of all pugs

- Hard to remove pigment once it occurs

- Progresses medial to lateral

prevent blindness

pigment keratopathy treatment goal?

- Topical cyclosporine or tacrolimus

- Topical dexamethasone

- Lubricant

- Medial canthoplasty

What is the treatment for pigment keratopathy?

Limbal melanocytoma

What am I describing?

- Brown opacities

- Bi-modal age distribution (3-4y, 7-10y) and aggressiveness (rapid in young, slow in old)

- Seen in German shepherds, golden retrievers, and labradors

Refer

What is the treatment for limbal melanocytoma?

Feline corneal sequestrum

What am I describing?

- Brown opacities

- Necrotic stroma

- FHV-1 may play a role

- Can vascularize and slough

- Topical antibiotics if ulcerated

- Cycloplegia

- Analgesia

- Surgery only definitive tx -- REFER

What is the treatment for feline corneal sequestrum?

Surgery

What is the treatment for dermoids?

Brown

What color opacity is seen with a dermoid?

benign, congenital growth of skin-like tissue (choristoma) in an abnormal location, often containing hair, sebaceous glands, and connective tissue.

what even is a dermatoid????

Brown

What color opacity is seen with an iris prolapse?

- Surgery

- Treats as an infected rupture

What is the treatment for iris prolapse?

- Hydropulsion

- Treat as a superficial ulcer

What is the treatment for superficial foreign bodies?

Surgery

What is the treatment for stromal, intraocular foreign bodies?

Lens capsule damage

What is an important prognostic indicator for stromal/intraocular foreign bodies?

As an infected stromal ulcer

How is corneal cellular infiltrate treated?

Fluorescein staining:

- Epithelium = no uptake

- Stroma = uptake

- Descemet's membrane = no uptake

How is corneal ulceration diagnosed?

loss of protective epithelium

Corneal Ulceration

- Superficial

- Not infected -- no infiltrate, organisms, or melting

- Heal in appropriate time (less than a week + minimal scarring)

- No complicating factors

Describe simple corneal ulceration.

- Broad-spectrum topical antibiotics TID

- Atropine (cycloplegic)

- Analgesic / anti-inflammatory

Goal - Prevent worsening while it heals on its own!

E COLLAR

What is the basic 3-pronged treatment for simple corneal ulceration?

- Loss of stroma

- Infected / melting -- infiltrate, organisms

- Slow to heal >1w

- Complicating factors (Ectropion, KCS, eyelid tumors, distichiasis, ectopic cilia, neuro, Diabetes)

Describe complicated corneal ulceration.

Is the dog visual? (PLR)

- If not —> enucleate

- If VISUAL, and no option for referral - nothing wrong with giving it a chance (especially in young, cats, no other ocular problems)

What is the first decision to make when treating complicated corneal ulceration?

Refer or not refer?

- If >50% depth, consider referral for surgical grafting

- LEAKAGE: If Seidel positive, immediate referral

What is the second decision to make when treating complicated corneal ulceration?

- Antimicrobials

- Atropine

- Analgesic / anti-inflammatory

- Serum anti-collagenase

(NO OINTMENTS)

What is the basic 4-pronged treatment for complicated corneal ulceration?

Indolent ulcers

What am I describing?

- Superficial ulcer

- No stromal loss

- Not infected

- Loose, non-adherent epithelium

- A stromal issue (failure to allow epithelial adherence

Boxers

What breed is predisposed to indolent ulcers?

- Topical analgesia

- Dilute betadine solution

- Debridement (cotton-tip debridement; diamond burr; grid keratotomy)

- Post-procedure management (e-collar, atropine, tetracycline, oral NSAIDs)

What is the treatment for an indolent ulcer?

FHV-1 keratitis

What is the most common cause of indolent ulceration in cats?

- Same as superficial ulcer (broad-spectrum topical antibiotics; atropine; analgesia) +

- Anti-viral therapy (Cidofovir)

- L-lysine

- Minimize stress

How are corneal ulcers due to FHV-1 keratitis treated?

Immune-mediated (poorly understood)

What is the etiology of episcleokeratitis?

- Cocker spaniels

- Collies

- Mixed breed dogs

What dog breeds are predisposed to episclerokeratitis?

- Parasitic granuloma (Onchocerca)

- Neoplasia

- Foreign body

What are 3 differential diagnoses for episclerokeratitis?

Episclerokeratitis

What am I describing?

- Immune-mediated

- Raised episcleral masses +/- vascular infiltrate in the perilimbal cornea

Immunomodulatory:

- Topical dexamethasone TID

- Topical cyclosporine or tacrolimus TID

- If poor response to topicals, can do oral or subconjuntival of cryotherapy

What is the treatment for episclerokeratitis?