Cornea Flashcards
Sensory to cornea
- V
Characteristics of corneal epithelium (pigmentation/myelination)
- Not pigmented
- Not myelinated
Which layer of cornea provides the most strength?
- The stroma
What’s the inner layer of the cornea?
- Endothelium
How thick is the endothelium of the cornea?
- 1 cell layer thick
Basement membrane of the corneal endothelium - name?
- Descemet’s membrane
What are three primary characteristics of the cornea?
- Refractile
- Densely innervated
- Transparent
Which layer of cornea is most densely innervated?
- Superficial layer most densely innervated
What keeps the cornea transparent?
- No blood vessels or pigment
- Nerves are non-myelinated
- in a state of relative dehydration (deturgescence)
What maintains the relative state of dehydration in the cornea?
- endothelial ATP pump
How thick is the corneal epithelium?
Approximately 4-9 layers of epithelial cells
Is corneal epithelium lipophilic or hydrophilic?
- Lipophilic - will not take up stain
Is corneal stroma lipophilic or hydrophilic?
- Hydrophilic and takes up fluorescein stain
What does exposed stroma indicate?
- Ulcer
How does the cobalt filter help with fluorescein stain?
- Excites it to make it more visible
What is a superficial corneal ulcer?
- Loss of epithelium only
- NO stromal loss
Appearance of superficial corneal ulcer
- Distinct edge
- Takes up stain (bright green)
- NO change in corneal contour
Pain of superficial corneal ulcer
- VERY PAINFUL
- Exposed nerves in superficial stroma
Function of corneal stroma
- Bulk of corneal thickness and tectonic strength
- Bundles of collagen fibers perfectly arranged and spaced for transparency
Appearance of corneal stromal ulcer?
- Hydrophilic –> + fluorescein stain
- Change in corneal surface or contour (depression
What is Descemet’s membrane?
Basement membrane of endothelium
Where is Descemet’s membrane?
- Deep to stroma
Is Descemet’s membrane hydrophilic or lipophilic?
- Lipophilic
- DOES NOT TAKE UP STAIN
What should you do if you see Descemet’s membrane?
- THIS IS TROUBLE
- IMPENDING GLOBE RUPTURE
- REFER IMMEDIATELY
- EMERGENCY
Which part of the corneal endothelium keeps the cornea dehydrated?
Na-K+ ATPase pump
What will happen if you lose corneal endothelium?
- Corneal edema
Regeneration potential of corneal endothelial cells
- DO NOT REGENERATE
- Cell #’s and function decrease with age
What does the cornea lack to maintain transparency?
- Lymphatics
- Pigment
- Myelin
- Lymphatics
How is collagen oragnized in the corneal stroma to maintain transparency?
- They are arranged and spaced perfectly for transparency I guess
What do red, White/blue, and brown on the cornea correspond to?
- Red = blood vessels
- Brown = pigment
- White = corneal edema
What can cause corneal pigment?
- Pigmentation
- Melanoma
- Iris prolapse
- Sequestrum
What can cause blue or white appearance of the cornea?
- Blue is usually diffuse edema
- There can be cell infiltrate (inflammatory cells)
- Lipid deposition
- Calcium degeneration
What can cause redness in the cornea?
- Blood from vessels
- Blood out of vessels
- Hyphema
What will happen if blood vessels infiltrate the cornea?
- “Ghost” vessels will remain
- Permanent loss of corneal clarity
How does corneal epithelium maintain dehydration?
- Barrier against water entering stroma from the surface
How does corneal endothelium maintain dehydration?
- Water pump
- Pumps aqueous out of cornea and back into the anterior chamber
What two mechanisms can lead to corneal edema?
- Loss of either corneal epithelium or corneal endothelium
Normal corneal thickness in dogs, cats, and horses?
- 500-600 µM in dog and cat
- 1 mM in horse
Appearance of corneal edema?
- Thickening of the cornea
- Blue or white appearance
What are causes of corneal edema secondary to endothelial dysfunction?
- Corneal endothelial dystrophy
- Glaucoma
- Uveitis
- Trauma
- Immune mediated
Blue eye - what is it?
- Generalized corneal edema resulting from endothelial damage from immune complexes due to Adeno1 virus (hepatitis) vaccine or wild strain
- Rarely does but can occur due to Adenovirus 2 vaccine
Which breed group will most commonly get blue eye?
- Sight hounds
Signs of corneal ulcerative diseases
- PAIN
- Epiphora
- Blepharospasm
- Photophobia
- Head shy or avoidance
- Miosis
- Enophthalmos
- Conjunctival hyperemia/chemosis
Causes of corneal ulcers
- Trauma
- KCS
- Exposure (lagophthalmos)
- Facial nerve paralysis
- Immune mediated
- Infectious agents (herpes in cats)
- Metabolic
- Dystrophic
- Neutrophic
- Chemical (chlorhexidine, alcohol, shampoo, acid, base)
Causes of corneal trauma in domestic animals
- Scratch/laceration/perforation
- Foreign body
- Ectopic cilia
- Eyelid abnormalities
- Caustic agents
Treatment of a corneal flap
- Suture in place or if superficial (<1/3 thickness) it can be excised
- REFERRAL PROCEDURE
Treatment for corneal perforation and lens laceration
- Surgical repair of the perforation
- Likely removal of the lens by phacoemulsification (if cataract is present)
- THIS IS REFERRAL AND EMERGENCY
What can happen if suture material is left exposed over the conjunctiva?
- Irritate or ulcerate the cornea
Splinter foreign body treatment
- Make sure it’s not full thickness and no fibers left in the tract
- Plant hulls you can try to flush out, but if not, must refer
- Referral procedure
Distichia temporary removal - why do?
- can be temporarily plucked until the ulcer heals
- Ultimately will grow back
Which infectious disease is a PRIMARY cause of corneal ulceration in cats, dogs, and horses?
- Herpesvirus
Are most causes of corneal ulceration primary or secondary?
- SECONDARY MOST OFTEN
Why are animals with KCS at increased risk of corneal ulceration?
- Epithelium dries out and loses integrity more quickly
Immune mediated keratitis appearance
- Blood vessels, edema, pigmentation
Differentials for immune mediated keratitis
- Neoplasia, infection
Chemical causes of keratitis
- Shampoo
- Alcohol
- Chlorhexidine
- Scrubs
- OTHERS
Treatment for chemical keratitis
- Keratectomy
- REFERRAL
Approach to corneal ulcer diagnosis and treatment
- STT prior to applying anesthetic or stain (not necessary if tears are streaming down the face)
- Fluorescein stain (examine in a DARK room with Cobalt filter and mag)
- Assess depth of ulcer (stroma?)
- Look for the cause of an ulcer (e.g. Entropion, dystichia, KCS, trauma)
- Is it infected (cytology) or melting?
What are the 5 steps of healing for a superficial corneal ulcer, and when do you expect them to occur?
- Epithelial cells at wound margin retract within the first hour
- Neutrophils from tear film arrive in the first 1-3 hours
- Epithelial cells slide and cover defect after 3-6 hours
- Mitosis to replace thickness in 1-2 days
- With appropriate treatment, an uncomplicated ulcer should heal in 3-5 days
Treatment for uncomplicated superficial corneal ulcer treatment?
- Topical antibiotic to prevent infection
- Atropine 1% topically for pain
- Oral pain medication
- E-collar!
What is a good choice of topical antibiotic in dogs and horses?
- BNP
What is a good choice of topical antibiotic in cats?
- Terramycin or erythromycin
- NOT BNP (Anaphylaxis and doesn’t work in cats)
When would you reach for ofloxacin for a superficial corneal ulcer?
- If there was an infection
Atropine 1% topical for superficial corneal ulcers - how does it work?
- Mydriatic and cycloplegic
- Prevents painful ciliary spasm
- Helps prevent reflex uveitis
- VERY IMPORTANT FOR HORSES BUT MUST MONITOR FOR COLIC
How much atropine to give topically?
- Use to effect (dilation)
- Often ONE application for an uncomplicated ulcer is adequate
Contraindications for topical atropine?
- use sparingly with KCS as it will decrease tear production
- Do not use with glaucoma as it may increase IOP
How long can atropine last in dogs and horses?
- 1-7 days in dogs
- 14 days in normal horses
Oral pain management for superficial corneal ulcers - dogs
- Tramadol or gabapentin for dogs
- Buprenorphine for small dogs
- NSAIDs may delay healing - both topical and oral but needed with uveitis
- Morphine can be compounded into a topical solution
Oral pain management for superficial corneal ulcers - cats
- Buprenorphine for cats
- NSAIDs may delay healing - both topical and oral but needed with uveitis
- Morphine can be compounded into a topical solution
Oral pain management for superficial corneal ulcers - horses
- Flunixin (IV or oral)
- NSAIDs may delay healing - both topical and oral but needed with uveitis
- Morphine can be compounded into a topical solution
Caveats of NSAIDs and when to use
- May delay healing (topical and oral applications)
- Needed with uveitis
Steroids with superficial corneal ulcers
- DO NOT USE
- Oral or systemic are both No-nos!
When to re-evaluate a superficial corneal ulcer?
- 5-7 days
What should you change if there has not been superficial corneal ulcer healing in 5-7 days?
- YOUR DIAGNOSIS
- NOT your antibiotic
At what point do blood vessels enter the cornea to try to heal a corneal ulcer?
7 days
Re-evaluation of non-healing ulcers - 3 steps
- Repeat STT
- Look for a missed cause: FB, ectopic cilia, distichia, lid abnormality, infection
- Look for loose epithelial edges (test with cotton swab
What does SCCED stand for?
- Spontaneous chronic corneal epithelial defect
Other names for SCCED
- Indolent ulcer
- Boxer ulcer
- Non-healing ulcer
Who gets SCCED? And what age?
- ANY breed over 5-6 years
- NOT a younger dog problem (except in Boxers, who can get it at any edge)
What is the primary defect with SCCED?
- Epithelium does not adhere to stroma
When to diagnose SCCED?
- I’m assuming you’d run a bunch of tests to rule out other things
- If no contributing factors can be identified on examination, that’s most likely an adhesion defect
Signs of SCCED?
- Wadded up on the edge of the ulcer
- Stain will go UNDERNEATH the epithelium
- Corneal blood vessels and edema
How much do corneal blood vessels travel per day approximately?
- 1 mm/day
Treatment for ulcers with unattached or loose epithelium
- Debridement to healthy attached epithelium with cotton tipped swab
- Contact lens if possible
- Pain management (morphine)
- E-collar
- Doxycycline maybe
- Topical antibiotic
- Atropine ONCE
When are contact lenses contraindicated?
- Not on deep ulcers or infected corneas
When do you refer a superficial uncomplicated ulcer?
- After appropriate treatment and ONE cotton tip debridement
If you have been treating an ulcer for 2 weeks and it has not healed, what is your next step?
- CONSULT WITH AN OPHTHALMOLOGIST
- REFER
- VERY PAINFUL
Grid keratotomy what is it?
- Superficial scraping of the stroma to debride epithelium??
- Painful and scarring
When should you do a grid keratotomy?
- UMM REALLY NOT RECOMMENDED!!!!
- Especially not with a young dog
When should you REALLY not do a grid keratotomy?
- Ideally never
- BUT ESPECIALLY NOT ON DEEP ULCERS, infected ulcers, cats, or horses
What is recommended to help with pain after a grid keratotomy?
- SHould be fitted with a contact lens after
- If you can’t do that, not recommended
What should you do if a superficial ulcer becomes a stromal ulcer in the face of treatment?
- REFER ASAP
- Doing something wrong or missing something
Treatment for an acute injury resulting in a stromal ulcer and when to refer?
- If it’s under 50% depth, treat AGGRESSIVELY
- If no improvement or worse in 48 hours, refer it
- If an ulcer is very deep, start treatment and recommend referral
What is a stromal ulcer?
- Any ulcer depth into stroma but not to Descemet’s membrane
- The cornea lacks strength so you MUST BE CAREFUL
Treatment for a stromal ulcer
- AGGRESSIVE MEDICAL TREATMENT
- Topical antibiotic q6 hr, serum, or EDTA
- E-collar, oral doxycycline
When is a surgical graft indicated for a stromal ulcer?
- If more than 50% depth or fails to heal with medical management, a surgical graft is indicated
- Requires MONTHS to regain normal strength
Descemetocele appearance
- Stain uptake around inner rim where the stroma is exposed, but not over Descemet’s membrane
Descemetocele treatment
- SURGICAL repair needed
Corneal perforation treatment
- IMMEDIATE surgical intervention and referral
- Corneal graft
- Conjunctival graft
- A-cell or Biosist graft
Here’s a reminder: should you ever use steroids on a superficial corneal ulcer?
NO NO NO
Why are steroids so bad for corneal ulcers?
- Promote collagenase activity
- Drive ulcer deeper leading to potential melting and perforation
- Inhibit PMN migration and adherence
- Suppress lymphocyte activity
- Delay healing
Appearance of a melting ulcer
- soupy mess
- Will rapidly progress to perforation
Treatment of a melting ulcer
- Anti-collagenase HOURLY
- Serum
- Tetracycline
- Oral doxycycline
- EDTA
- E-collar
- Acetylcysteine
Role of EDTA in treatment of melting ulcers
- Chelates divalent cations and reverses degradation process of the melting ulcer
How do cats respond with melting ulcer treatment in general?
- Very well
How do horses respond with melting ulcer treatment in general
- Poorly
Which topical abx to give for a melting ulcer?
- Neomycin/polymixin/gramicidin
Role of terramycin with melting ulcer tx?
- Anti-collagenase
Role of chloramphenicol in melting ulcer treatment?
- Penetrates cornea
- Reserved in general for horses
When to give doxycycline or clavamox orally for melting ulcer tx?
- Doxycycline, clavamox
Fluoroquinolones on a melting ulcer
- MAY promote melting
Surgical repair of melting ulcer
- Debride (surgically) unhealthy cornea
- Conjunctival graft to provide blood supply and strength
WHo should perform corneal surgery?
- ONLY board certified ophthalmologists or ophthalmology residents in training
Explain rotating conjunctival graft for corneal defects
- Very thin layer of conjunctival epithelium is bluntly dissected from the bulbar conjunctiva and sutured to the cornea
- Magnification and 8-0 suture are used
- The graft can be cut down in 6-8 weeks after healing
Describe the main characteristics of german shepherd pannus
- Sub-epithelial inflammatory cell infiltrate
- Proliferation of blood vessels
- Corneal edema
- Pigmentation
Is GSD pannus normally ulcerative?
- Usually not
Causes of german shepherd pannus
- Immune-mediated
- Exacerbated by UV light
Where does GSD pannus usually start on the eye?
- Usually starts laterally but is progressive if not controlled
Which breeds get pannus in general?
- GSD
- Belgian Tervuren
- Greyhound
- Border collies
Breeding animals with pannus?
- Don’t do it
What will happen once you get pannus under control?
- Pigment persists, with regression of blood vessels, edema, and cell infiltrate
How long must you manage pannus?
- FOREVER
Treatment principles for pannus
- Aggressive steroids (Prednisolone acetate or NPDex every 6-8 hours and tapered to control)
- Cyclosporine or tacrolimus twice a day
- Dog goggles and avoid UV light
- Oral doxycycline may be helpful initially in severe cases
- Exclusion diet such as Z/D might help to redcue antigenic stimulation
Who gets pigmentary keratitis?
- Brachycephalic breeds with exophthalmos and lagophthalmos
What is lagophthalmos?
- Inability to close the eyelid over the eye completely
What causes pigmentary keratitis?
- Chronic injury or irritation to the cornea
- Exposure
- Aberrant cilia
- KCS/poor tear film
What do you think about putting steroids on a brachycephalic dog, especially with pigmentary keratitis
- Don’t do it
Appearance of pigmentary keratitis?
- Pigmentation on the eye
How does cyclosporine help dry eyes?
- Tear production
- Tear film quality
- Reduces corneal pigmentation
Treatment for pigmentary keratitis
- Protect cornea with lubrication and reducing palpebral fissure size
- Eliminate cause of possible (trichiasis, KCS, eyelid mass)
- Intervene before pigmentation causes visual loss (refer early)
- Cyclosporine or tacrolimus
Dermoid
- Skin growing in an abnormal ocation
Treatment for dermoid
- Surgical excision (superficial keratectomy)
- REFERRAL PROCEDURE
Corneal subepithelial lipid dystrophy appearance
- Lipid deposit
- It’s on the cornea not the cataract
- May be horseshoe shaped
- Can get brittle
- Don’t breed
Characteristics of corneal subepithelial lipid dystrophy
- Hereditary
- Bilateral
- Non-painful
- Progressive
Treatment for corneal subepithelial lipid dystrophy
- Low fat diet to reduce the cholesterol crystal deposits
Pathophys of corneal subepithelial lipid dystrophy
- Calcium deposits over the cholesterol crystal can lead to corneal degeneration?
Plasmoma
- Depigmentation and thickening of the third eyelid due to inflammatory cells (plasma cells) infiltrating the area
Limbal melanoma
- Don’t take the eye out
- Don’t often metastasize
- Refer?
- GSD and labs get it
Corneal SCC in a horse tx
- Keratectomy or freeze
- Could be malignant
What can be long term side effects from cyclosporine/tacrolimus?
- Squamous cell carcinoma
