Lecture 6: Cornea

What is the most densely innervated structure?

Cornea

Where are more nerve endings found?

In epithelium/superifical cornea

What nerve innervates the cornea?

Trigeminal (CN V)

What breeds have decreased cornea innervation?

Brachycephalics

What stimulates the reflex stimulation of CN V to anterior uveal tract?

Any stimulation of the corneal nerves

What does all keratitis create?

Some degree of reflex uveitits

What causes corneal ulcers

Stimulation of CN V to→ reflex uveitis with painful ciliary body muscle spasm

How can you relieve painful ciliary body spasm?

Cycloplegic drug (atropine)

True or false, stormal and epithelial wounds heal the same

False

What are the characteristics of epithelial wound healing?

• Epithelial cells lose adhesion to basement membrane

• Mitosis w/increased cell numbers

• Migration of cells until defect close

• Re-establishment of basement membrane adhesion

Compare and contrast epithelial and stormal wound healing

• Epithelial healing

  • Happens quickly

  • Minimal fibrosis hence minimal loss of transparency

  • No treatment currently available to speed epithelization

• Stormal healing

  • Happens slowly

  • Requires activation, transformation, and migration of keratocytes into fibroblasts

  • May require vasculization

  • Fibrosis intially, followed by collagen synthesis

  • Epithelization proceeds resolution of stormal remodeling

What are the 2 pathologic states of corneal disease?

1. Loss of transparency

2. Loss of thickness

Match the letter with the right number

1. Flurescien sodium

2. Epithelium

3. Stroma

4. Descemet’s membrane

A. Hydrophilic

B. Hydrophobic

1. Hydrophilic

2. Hydrophobic

3. Hydrophilic

4. Hydrophobic

Characteristics of simple corneal ulcers

• Superficial

• Not infected

• Heal in appropriate amount of time

• No complicating factors

What should you look for to tell if a corneal ulcer is infected?

Cellular infiltrate in stroma and/or a melting stroma

When should normal corneal ulcers heal?

About a week

What are some common complicating factors?

• Entropion

• KCS (dry eye)

• Eyelid tumors

• Lagophthalmos

• Ectopic cilia

• Trigeminal neuropathy

• Systemic disease (ie. Cushings, diabetes mellitus)

• Distichiasis

What is the most important pinciple of superficial ulcer treatment?

You aren’t actually making the ulcer heal

What should you use to treat superifical ulcer?

• Broad spectrum topical antibiotics

• Analgesia (3-5 days)

• E-collar to prevent self trauma

When should you recheck normal dogs with superifical ulcers?

5-7 days

When should you recheck brachycephalic dog with superifical ulcer?

2-3 days

Why do you have to recheck brachycephalic dogs sooner?

- Decreased corneal sensation

– Lagophthalmos

– Evaporative keratitis (from

not blinking)

– Increased incidence of KCS

– More likely to experience

complications in healing

What are characteristics of complicated ulcer?

• Deep (loss of stroma)

• Infected/melting

• Complicating factors present

• Slow to heal

Stormal loss

Corneal perforations with fibrin plug

Melting ulcer

How do you treat complicated ulcer with stormal loss?

• Surgical grafting (Stormal loss >50% or cornea is perforated)

• Rule out infection (C/S or cytology)

• Control any infection (Topical antibiotics Oflaxacin, Tobramycin, Cefazolin)

• Control secondary uveitis (atropine topical 1%)

• Provide analgesia (Tramadol or gabapentin)

• Topically anti-collagenase/protase

• E-collar

• Oral sedatives if necessary

• Parital temporary tarsorrhaphy

How do you treat a perforated cornea?

• Broad spectrum antibiotic (Clavamox)

• Partial temporary tarsorrhaphy

• No ointments

• No topical atropine

How do evaluate a patient with a corneal peroration?

1. Does the eye have poetical to see

2. Is the perforation sealed

How do you treat an ulcer with complicating factors?

• Treat the complicating factors

• Treat as simple ulcer once complicating factors are resolved

• When in doubt question the diagnosis not the treatment

Superifical, loose, non-adherent epithelial flaps. Usually limited vascularization.

Indolent corneal ulcers

Pathogenesis of indolent corneal ulcers

Failure of normal adhesions between epithelium and its basement membrane and underlying stroma

Treatment of indolent ulcer

• Diamond burr diabridement or grid keratomy

• ± sedation

• Topical anesthesia

• Cotton tip applicators

• E-collar

• Atropine

• Broad spectrum antibiotic (Terramycin or doxycycline)

• Analgesia

What indolent ulcers should you not grid or burr?

Complicated ulcers or cats

Most common cause of corneal ulcers in cats. Remains dormant in neurons until elicited by a stressful event. Dendritic ulcers are a classic sign.

Feline herpesvirus-1

Treatment of FHV-1 ulcer

• Topical Cidofiovir

• Systemic anti-viral (Famciclovir)

• L-lysine

• Minimize stress

Bilateral, non-painful, non-progressive. Does not interfere with vision. Seen in purebreeds.

Corneal dystropy

Unilateral or bilateral, usually asymmetric. Associated with concurrent ocular surface or intraocular disease. systemic implications (hypothyroidism, hyperlipidemia). Often associated with ulceration of overlying epithelium

Corneal degeneration

How do you treat corneal degeneration?

• ID any concurrent ocular or systemic disease and treat

• Strongly consider referral

Disorganized collagen. Associated with previous keratitis. Maybe associated with vascularization and pigmentation. Nonpainful. Does not need treatment.

Corneal fibrosis

Can be tan, brown, or white if chronic. Clumps of inflammatory cells/protein/fibrin that adheres to endothelium. Pathognomonic for anterior uveitis. May have a lipid component

Keratin precipitates

Epthelium natural barrier to edema.

Corneal edema

Differential diagnosis for corneal edema

• Ulcerative keratitis

• Non-ulcerative keratitis

• Keratic precipitates

• Anterior lens luxation

Differential diagnosis for diffuse corneal edema

• Glaucoma

• Anterior uveitis

• Endopthlamititis

• Endothelial dystrophy

• Senile endothelial degeneration

• Immune mediated endotheliltis

• Blue eye CAV I (very rare)

What diseases of the corneal can lead to corneal edema?

• Corneal endothelial dystrophy (breed-related, middle aged dog)

• Senile endothelial dystrophy

What breeds are commonly affected by corneal endothelial dystrophy?

Bostons, Dachshunds, Chihuahua, Basset hounds

How do you treat endothelial dystrophy and endothelial degenation?

• Topical hyperosmotics

• Keratoleptenesis

• Thermokeratoplasty

What are almost all red corneal opacities?

Vascularization of the cornea

What disease is associated with corneal vascularization?

• Ulcers involving stormal loss

• Indolent ulvers

• KCS/dry eye

• Intraocular disase

• Pannus

• Eosinohphilic keratitis

Immune mediated corneal disase of german shepherds, mixes, and sight hounds

Pannus (aka chronic superifical keratitis)

CS of pannus

• Superifical vascularization

• Pigmentation

• Corneal degeneration

• Fibrosis

How do you treat pannus?

• Topical prednisolone

• Topical cyclosporine

• Recheck in 2 months

• Best can manage on CSA or tacrolimus alone

• Liefelong treatment

May be related to FHV-1. Raised pink/white plagues extending from limbus towards the axial cornea with associated vascularization. Variable ocular pain. Usually unilateral.

Eosinophilic keratitis

How do you treat eosinophilic keratitis?

• Cyclosporine or tacrolimus

• Topical megaestrol acetate

• Megestrol acetate

• Topical steroids

• L-lysine

Brown pigment is:

A. Specific

B. Non-specific

B. Non-specific

What diseases are associated with pigment?

• Pigmentatary keratopathy

• Adnexal neoplasia/entropion and chronic endema

A genetic disease in pugs. Goal is to prevent pigment from covering entire cornea

Pigmentatory keratopathy

Medical treatment of pigmentatory keratopathy

• Treat any associated KCS

• Immunodulatory meditators (Cyclosporines)

• Topical steroids are dangerous

• Lubricants

• Treatment is lifelong

Surgical treatment of pigmentary keratopathy

Medial canthoplasty (correct entropion, decreased lagopthalmos)

3-4 years old and 7-10 years old. German shepherds, goldens, and labs. Tend to be more aggressive in younger dogs.

Limbal melanoma

What animals are predisposed to corneal feline sequestrum

Brachycephalic cats

Feline corneal sequestrum treatment

• Keratectomy to remove lesions (<50%)

• Grafting procedure (>50%)

• Support topical antibiotic

• analagesia with intermittent topical atropine