The Cornea Flashcards
What are the 4 layers of the cornea?
- Epithelium
- Stroma
- Descemet’s membrane
- Endothelium
Why is the cornea clear?
- Avascular
- Non-myelinated nerves
- Dehydrated
- Ordered cell arrangement
- Non pigmented
What do lipids on the cornea look like, and what is it suggestive of?
shiny, bilateral, crystalline
indicative of corneal dystrophy
What are the possible causes of corneal edema resulting in a blue opacity of the cornea?
- Epithelial barrier disruption (tear film entry into hydrophilic stroma)
- Endothelial barrier/pump dysfunction (Focal loss, reduction in number, reduction in function)
What is an example of corneal edema resulting from generalized reduction in function of endothelial cells?
- Glaucoma
- Uveitis
What is an example of corneal edema resulting from generalized reduction in number of endothelial cells?
Senile endothelial degeneration
(Edema displays a fluffy and disorganized pattern)
What does a red corneal opacity indicate?
Corneal neovascularization
What are causes of superficial neovascularization resulting in red opacity of the cornea?
Anything that irritates the surface of the eye
Ex: KCS, entropion, hair abnormalities, superficial corneal ulcers
What are causes of deep neovascularization resulting in red opacity of the cornea?
- Uveitis
- Glaucoma
- Deep corneal ulcer / inflammation
What does ciliary flush indicate, and how does the eye appear?
360 degree red halo around the cornea, indicates deep neovascularization (uveitis, glaucoma, deep corneal ulcer/inflammation)
What color change of the cornea can be seen with corneal fibrosis?
White with gray or wispy features
What causes the cornea to appear chalky white?
Calcific corneal degeneration
What color change to the cornea is indicative of corneal infection?
White with green or yellow hues (WBC infiltrates)
List the 4 brachycephalic risk factors for corneal ulcers
- Ocular prominence (bug eyes)
- Decreased corneal sensitivity
- Adnexal abnormalities (lagophthalmos, trichiasis, distichia, etc)
- Tear film abnormalities (prone to dry eye)
What is the definition of a uncomplicated/simple corneal ulcer?
A superficial ulcer that heals in 7 days or less
What are causes of delayed corneal ulcer healing, resulting in a complex/complicated ulcer?
- Indolent ulcers
- Persistent irritation
- Infection
What is the treatment protocol for a patient with an uncomplicated superficial corneal ulcer?
- E collar
- Topical Abx TID/QID (neopolyBAC, Tobramycin)
- Atropine
- NSAIDs/Tramadol/GABA
- Recheck 5-7 days
What is the definition of a complicated/complex corneal ulcer?
A superficial corneal ulcer that takes longer than 7 days to heal
Why do indolent ulcers result in delayed healing?
Lack of epithelial adherence to stroma (lack of hemidesmosomes)
How can indolent ulcers be diagnosed?
- Test epithelium with q-tip
- Indolent ulcers have epithelium that is easily peeled off/debrided with q-tip
- Fluorescein staining results in a halo extending beyond epithelial margins
What dog breed is most susceptible to indolent ulcers?
Boxers
What is the treatment protocol for indolent ulcers?
Medical management: Topical Abx, Atropine, NSAIDs
1. Debridement with q tip (50% chance of healing within 2 weeks)
If not healed by 2 weeks…
2. Anterior stromal puncture
3. Diamond burr debridement
4. Recheck in 2 weeks
When is anterior stromal puncture and diamond burr debridement contraindicated?
If ulcers with signs of infection
(Never do if suspect infection!!)
What is the most common cause of corneal infection in cats?
Feline herpesvirus
(bacterial and fungal can be causes too)
What corneal ulcers have concurrent corneal infection, 99% of the time?
Deep (stromal) corneal ulcers
What is the pathogenesis behind corneal infection?
Bacteria (most commonly) or fungal organisms results in collagenolysis and keratomalacia
What bacterial organisms are most commonly involved in corneal infections?
- Pseudomonas (most common cause of melting corneal ulcers)
- Staph
- Strep
What are common clinical findings in patients with corneal perforation?
- Positive Seidel test (active leaking)
- Wrinkled cornea
- Shallow anterior chamber
- Iris prolapse
- Fibrin plug
- Hyphema
What tests should NOT be performed in patients with deep corneal ulcers?
- No STT or IOP (painful)
(can perform in normal eye tho)
Why is proparacaine never sent home for management of corneal ulcers?
Repeated use is toxic to the cornea, may result in melting ulcer
What indications require surgical treatment of corneal ulcers?
- > 50% stromal loss or severe infection
- If refractory to medical therapy
- If descemetocele or perforation
When are systemic antibiotics indicated for treatment of deep corneal ulcers?
- Well vascularized ulcer
- Corneal perforation
- Post conjunctival flap surgery
What options are available for medical management of corneal ulcers?
- Topical Abx (Cephalosporins, Fluoroquinolones)
- Autologous serum
- Topical atropine
- NSAIDs
What ulcers always require referral for surgical correction?
- Corneal perforation
- Descemetocele
What is the cause of greasy/tan punctate opacities on the cornea?
Keratic precipitates - common with uveitis
