21.10: Ophthalmology Flashcards
Corneal ulcer
break in continuity of the corneal epithelium with exposure of the underlying stroma.
What is the difference between a corneal ulcer and ulcerative keratitis?
No difference - they are the same thing.
1
Epithelium
2
Stroma
3
Descemet’s membrane
4
Endothelium
How is corneal transparency retained?
- No keratin, blood vessels or melanin
- Low cell density
- Very regular arrangement of collagen fibrils
- Relatively dehydrated state
How is the relatively dehydrated state of the cornea maintained?
- Epithelium has tight junctions to prevent water from tear film entering
- Endothelium below has Na/K ATPase pump; this pumps ions from the stroma into aqueous humour
What happens if water gets into the stroma of the cornea?
- Corneal oedema develops
- The collagen fibrils are distorted, resulting in opacity
Superficial corneal ulcer
There is loss of the epithelium only.
* Cells slide rapidly over to cover the defect
* Within hours-days there is cell proliferation, migration and adhesion
Describe the process of healing for a stromal ulcer
- This takes longer than a superficial corneal ulcer to heal
- The epithelium must grow over the deficit before the stroma can begin to heal
- Once re-epitheliasisation is complete, fibroblasts migrate in and lay down new collagen
- Requires vascularisation
- Results in scar tissue -> remodelling occurs over time
What are some possible causes of corneal ulcers?
- Trauma
- Tear film problem (e.g. KCS)
- Adnexal conditions
- Primary corneal disease (e.g. SCCEDs)
- Infection
- Neuro disease
What might have caused these ulcers?
These ulcers occurred secondary to keratoconjuctivitis sicca
* These ulcers have a circular ‘punched out’ appearance and deteriorate rapidly
Entropion
Eyelid mass
Ectopic cilia
Pug with macropalpebral fissure resulting in lagophthalmos and exposed cornea
Shih tzu with triachiasis resulting from pronounced nasal fold
Spontaneous Chronic Corneal Epithelial Defects which can cause corneal ulceration
These are especially common in Boxers and are often un-healing.
Only epithelium is lost but it fails to adhere to underlying stroma - reason unknown.
Recurrence a common ssue.
Cat with corneal ulcer due to neurotropic keratitis
Neuroparalytic keratitis
Facial nerve paralysis which results in inability to blink
Neurotrophic keratitis
Trigeminal nerve problem where there is reduced or absent corneal sensation so the animal does not blink. This is highly likely to cause ulceration.
Rare.
a) Brachycephalic conformation
b) Entropion
c) Distichiasis
d) KCS
e) FHV-1
B) Entropion
Seen in some older cats
Causes ulcers
Which cranial nerves does the palpebral reflex test?
- Trigeminal - eyelid sensation
- Facial - blinking
True/false: exposed Descemet’s membrane will take up fluorescein stain.
False!
Descemet’s membrane does not take up fluorescein stain
What are the clinical signs of corneal ulceration?
Descemetocoele
Keratomalacia
True/false: steroids are a good first line treatment for corneal ulcers.
False!!!!!!!
Topical steroids cause local immune suppression and potentiate collagenase activity.
Never use steroids with a corneal ulcer!
SCCED
L arrow = stromal ulcer
R arrow = descemetocoele
Melting ulcer
Perforated ulcer
What questions should you ask yourself when dealing with a corneal ulcer?
Treatment of a simple superficial ulcer
Avoid topical NSAIDs as these may delay healing.
Treatment of SCCEDs
Treatment of melting ulcers
True/false: grid keratotomy is a good idea for a non-healing ulcer in the cat.
False
Never grid a cat’s cornea!
Which of the following animals would have the best prognosis following a globe prolapse?
a) Cat
b) Greyhound
c) Shih Tzu
d) Spaniel
c) Shih Tzu
Retrobulbar abscess
In cases of glaucoma, we need to reduce IOP. What drugs can we use to do this?
- Prostglandin analogue (e.g. latanoprost) if suspeced primary glaucoma, not for lens luxation
- Carbonic anhydrase inhibitors (e.g. brinzolamide, dorzolamide) always OK but may not be enough on their own
- IV mannitol used to be drug of choice but less so now
Also provide analgesia, seek referral advice or send animal there, consider referral assessment of the other eye because primary glaucoma = bilateral condition.
What signs of glaucoma might we see on ocular exam?
Anterior lens luxation
Which animals cope better with anterior lens luxation - dogs or cats?
Cats cope better.
Anterior lens luxation is an emergency in the dog!
Differentials for sudden onset blindness
- Acute glaucoma
- Acute uveitis
- Intraocular haemorrhage
- Retinal detachment
- Optic neuritis
- Sudden Acquired Retinal Degeneration (SARD)
- Toxicity: ivermectin, enrofloxacin in cats
- Intracranial lesion
May need specialist equipment e.g. electroretinogram (ERG) or MRI to make diagnosis
