Ocular disease small ruminants Flashcards
Small ruminant orbit type
Enclosed
What enzyme do small ruminants have in their tears that cattle don’t
Lysozyme
GLobe and cornea shape
Globe is sphercal
Corneal is elliptical
How will a small ruminant move in they have unilateral blindness
Will turn head to side to see forward using contralateral eye
Which cranial nerves does the menace response evaluate
Optic nerve (II)
Facial nerve (VII)
What nerves does the palpebral reflex evaluate
Trigeminal (IV)
Facial (VII)
Pupillary light reflex what nerves/areas
Needs functioning retina, optic nerve (II), oculomotor nerve (III) and midbrain
What is the PLR like in cortically blind animals
Normal
Which reflex may be missing in <2 week old lambs/kids due to being acquired
Menace
Distichiasis vs trichiasis
Distichiasis = double set of eyelashes
Trichiasis = eyelashes rubbing on cornea/ingrowing
How do we examine the nictitating membrane for foreign bodies
Pull lower eyelid down and retropulse the globe
What should we use to flush the eye and what might we use if before surgery
Sterile saline
If before surgery can use povidine iodine (NOT CHLORHEXIDINE)
What procedures can be done to act like a /bandage’ over corneal ulcer to air healing
Third eyelid flap
Tarsorrhaphy
What does tarsorrhaphy mean
Closing together part of the two eyelids to keep part of eye shut
How does primary/congenital entropion present
Just lower eyelid affected
Bilateral usually
WHat can lead to acquired/secondary entropion and how does it present
Presents unilateral usually; can be upper or lower eyelid
E.g from trauma, microphthalmia, severe dehydration, loss of retrobulbar fat, painful eye conditions that cause retraction of eye
three non-surgical ways to correct entropion
- INjection of irritant locally to cause fibrosis e.g penicillin
- Application of haemostat to cause irritation
- Non-absorbable vertical mattress suture placement
When would we consider surgical correction of entropion
Non-surgical methods haven’t worked
Animal is at least 4-6 months old; time for facial maturity to potentially correct issue
Is entropion heritable
Yes but unclear how
Don’t use these animals for breeding
What can cause ectropion
Iatrogenic overcorrection of entropion
Trauma
How would we surgically correct ectropion
V to Y blepharoplasty or eyelid shortening
What management factor predisposes to periorbital eczema and how
Too little space at feed troughs
So get overcrowding, trauma to skin, Staph aureus bacterial infection
–> Swollen eyelids which block vision
Is fungal blepharitis more common in sheep or goats
Goats
- Dermatophytosis from Microsorum/Trichophyton
What viruses could cause blepharitis
Orf, sheep and goat pox
Bluetongue
In what disease course might we see third eyelid prolapse
Tetanus
What parasite can cause nasolacrimal duct disease
Oestrus ovis
Via aberrant migration
What does a soft looking globe/flat anterior segment suggest has happened
Corneal or scleral laceration
What are the two primary aetiological agents in infectious keratoconjunctivitis/pink eye
Mycoplasma conjunctivae
Chlamydophila pecorum
What test do we need to identif M conjunctivae
PCR
Routine bacteriology won’t detect it
Mycoplasma conjunctivae recovery
Usually resolves in a few weeks without treatment BUT immunity is poor so common to get relapses
Which antibiotics would we use to speed the recovery of mycoplasma conjunctivae
Tetracyclines
Which secondary consequence of chlamydial keratoconjunctivitis can be seen in lambs
Polyarthritis
COntinued shedding of chlamydial vs mycoplasma keratoconjunctivitis
Months
Causative agent of silage eye
Listeria monocytogenes
Clinical signs of silage eye
Blepharospasm, corneal oedema, hypopyon (white fluid layer of WBCs on bottom of anterior chamber)< miosis, catarrhal conjunctivitis
What systemic diseases could lead to yellow coloration of the eye
Haemolytic diseases e.g copper toxicity, liver dosease (pyrorolizidine toxicity, liver fluke)
What is bright blindness and what is the cause
= progressive retinal degeneration
Due to chronic grazing of bracken fern
Notice hyper-reflectivity of the tapetum lucidum
Which sheep breed is associated with inherited microphthalmia
Texel
What is the cause of progressive retinal degeneration
Vitamin A deficiency
(rare in grazing animals since they can convert beta carotene from plants into vit A0
WHat is ceroid lipofusinosis
Inherited lysosomal storage disease in south hampshire sheep that cause retinal degeneration
What infectious diseases can cause retinal disease in neonates
What about adults
Neonates: border disease virus, congenital toxoplasma infection, septicaemia listeriorisis, bluetongue
Adults: scrapie
