Ruminant Ophthalmology Flashcards
ruminant fundi - arteries
Cows and sheep
* 3-4 major arterioles with venules
* come off at right angles
* Kidney bean-shaped optic disc
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Goat
* More major arterioles
than cow/sheep
* 15-30 minor arterioles
* Round optic disc
(cow > sheep)
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Camelids
* 3-4 major arterioles with venules
* 15-30 minor arterioles
* Right angles
* Atapetal
Ocular examination - dilation method
Ruminants: use atropine 1%, Camelids: use tropicamide.
Local Blocks
1. Auriculopalpebral nerve block
- Auriculopalpebral nerve block
* Motor only to upper eyelid
* Zygomatic arch
> Where the a-p nerve
crosses the zygomatic
arch.
> 6 mg/kg. 5-6 ml 2% lidocaine hydrochloride
* WDT: mean and milk = 24 hrs
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Peterson block
- Peterson block
- Analgesia to the orbit and globe but not eyelids
(CN III, IV, V1,2,3, VI)
- Results in: mydriasis without PLR
- Slightly curved 10 cm 18 ga needle
- 15-20 ml lidocaine
- Risk of death if injected into blood vessel/dural sheath therefore aspirate before injection.
- Directed from the notch between the zygomatic arch and the supraorbital bone towards the back of the eye.
- Direct the needle straight in until the mandibular ramus is touched, then redirect the needle forward toward the back of the globe
(pterygopalatine fossa). Often you can see the eye move in response.
Four-point block
- Analgesia to the orbit and globe (CN III, IV, V1,2,3, VI) but not eyelids.
- 6 cm” needle inserted between orbit and globe (trans conjunctival/trans palpebral) 12, 3, 6, 9 o’clock position: 5-10 mls lidocaine at each site.
- Safer than Peterson Block
Eyelid Line block
- local infiltration of 2% lidocaine above the upper eyelid incision and below the lower eyelid incision.
- avoid large volumes as it will distort the eyelid tissues.
Strabismus - etiologies, C/S
- Abnormal ocular globe position
<><> - Hereditary (Holstein, Jersey, Ayshire, German Brown, Swiss, Shorthorn)
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Acquired - Orbital neoplasia (LSA)
- CN dysfunction from listeriosis,
- Polioencephalomalacia
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C/S: - Divergent (exotropia)
- Convergent (esotropia)
Strabismus + exophthalmos - Shorthorns can be
progressive - If severe: visual impairment
Nystagmus
etiolgies
Constant oscillating horizontal movement of the ocular globe
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Hereditary congenital:
* Ayrshires, Guernsey’s, and Holsteins
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Acquired:
* Calves that develop dysfunction of their
peripheral vestibular system or cerebellum
following an ear infection or systemic disease
* Can be seen with listeriosis, MCF, PEM, rabies
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Treatment: none
Microphthalmia
etiologies, clinical signs
- Congenitally small eyes
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Inherited or acquired - BVD - unilateral or bilateral
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Clinical Signs: - small ocular globe
- protrusion of third eyelid
- small palpebral opening
- iris anomalies
- cataract
- retinal detachment/dysplasia
Treatment: enucleation (to reduce
infection)
Entropion
- etiology
- clinical signs, treatment
- The inversion of eyelids (usually lower)
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Neonatal cattle
Secondary - systemic diseases (dehydration, wt
loss) - corneal ulcers
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Clinical signs (uni/bi): - lacrimation from irritation
- corneal ulceration
- conjunctivitis
- vision deficits (if bilateral)
- reduced growth/weight gain
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Treatment: - tacking sutures (temporary)
- Hotz-Celsus (permanent)
- Temporary correction with placing vertical mattress sutures (tacking sutures)
- Permanent correction with removal of a skin crescent with wound closure (Hotz-Celsus)
- Topical antibiotics and atropine if corneal ulcers present
Conjunctiva and Cornea
Dermoid
- what is it?
etiology, clinical signs, tx
Ectopic skin cells
* Hair follicles, skin glands
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Third eyelid, conjunctiva, cornea
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Herefords
* Genetically predisposed
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C/S: Epiphora
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Treatment:
* Surgical excision
(superficial keratectomy)
Infectious Bovine Keratoconjunctivitis (IBK) = “pink eye”
- causes, transmission
Calves: predominately
Moraxella bovis
* Gm-negative bacillus
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Secondary pathogens
* Mycoplasma and IBR
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Transmission: flies
> Summer outbreaks, indoor housing winter
> Herefords, Hereford crosses, Murray Grays
* Highest susceptibility
Infectious Bovine Keratoconjunctivitis (IBK, “pink eye”) cont’d
clinical signs, progression
Initial stages:
Hyperemic conjunctiva
Blepharospasm
Serous discharge
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Progression:
Mucopurulent discharge
Corneal edema, ulceration, neovascularization
Corneal perforation
Secondary uveitis is also commonly seen
Infectious Bovine Keratoconjunctivitis (IBK, “pink eye”) treatments, prevention
Control the fly population
Isolate affected cattle
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Antibiotics:
* IM long-lasting tetracycline (q3d)
* Topical tetracycline (TID)
* Topical atropine (BID)
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Corneal rupture:
* Conjunctival flaps or enucleation
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Vaccination: debatable efficacy
Infectious Bovine Rhinotracheitis (IBR)
- clinical signs, dx, tx
Herpes virus
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C/S: Ocular and systemic (respiratory) disease
Mimics IBK ocular signs (serous-m/p discharge, conjunctivitis, corneal bv’s)
BUT no ulceration
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Dx: Viral culture or paired serum samples for titres
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Tx: Controlling secondary bacterial infections with topical antibiotic
ointments TID (tetracycline, BNP)
