Equine ophthalmology Flashcards
What is the location of lacrimal punta in horses
Dorsal and ventral
Where do drained tears go
Through canaliculi into nasolacrimal duct and out nasal ostium (next to pigmented/unpigmented skin in nose)
What are vibrissae
Very sensitive hairs
3 or 4 found dorsomedial to the upper lid
8-12 found ventral to lower lid
What are corpora nigra
Proliferation of iris tissue
More so dorsally than centrally
What is different about examining the iridocorneal angle in horses than cats/dogs
Canbe examined directly rather that needing to use a gonioscope
Where do we block the frontal nerve
Supraorbital fossa
Where do we block the auriculopalpebral nerve
Zygomatic arch
What do we block for eyelid akinesia
Auriculopalpebral nerve CN VII at zygomatic arch
What do we block for upper eyelid desensitisation
Frontal nerve; branch of trigeminal nerve
Characteristics of equine fundus
Paurangiotic with many vessels emanating short distance from the optic nerve
Tapetum is dorsal and fibrous
What are stars of winslow
Dots seen in the fibrous tapetum of horses which are end on choroidal capillaries
Why do we percuss sinuses during equine opthalmology exam
To check for space occupying lesions altering normal percussion
features of the menace response
Learned reflex so not present < 2 weeks old
Sensory is optic nerve, motor is facial nerve
+ involves visual cortex
Which reflex is a true test of vision
Menace reflex
Pupillary light reflex components
SEnsory = optic (II)
Motor = oculomotor (III)
No visual cortex involvement
Dazzle reflex components
Sensory = optic (II)
Efferent = facial (VII)
Doesn’t involve visual cortex = subcortical reflex
Does test retinal function
Palpebral reflex components
Sensory is trigeminal (V)
Motor is facia (VII)
What do we use to achieve mydriasis for ophthalmic examination
Tropicamide 1% - takes 10-20 mins to work
How does indirect ophthalmoscopy work
One operator holds lens close to horses eye and other holds light source near examiner
They function as a unit
Qualities of indirect ophthalmoscopy
Virtual image which is inverted and reversed
Larger field of view so easier detectino
Safer
Use 20D lens
Monocular vs binocular indirect ophthalmoscopy
Binocular uses head mounted light source so have two eyes and can get depth perception
Qualities of direct ophthalmoscopy
Upright image
Greater magnification
What do concave vs convex lenses on a direct opthalmoscope do
Convex = +ve lenses; bring position of focus closer to you to look at more anterior things
Concave = -ve lenses; brings focus further away to look at more posterior things
What dioptre setting do we use for distant direct ophthalmoscopy
0 dioptres
What dioptre setting is the fundus in focus at
Between 0 and -2D
When to avoid tonometry
Fragile eyes e.g laceration, deep corneal ulcer due to risk of rupture
What type of tonometer is tonovet
REbound
What is a subpalpebral lavage system
Used to apply topical mediations to the eye in head shy horses or where frequent application needed and not easy to do
Involves placement of a footplate under upper or lower eyelid
How to repair eyelid lacerations
Close in 2 layers; first deep subconjunctival layer then skin layer
What is the antidromic reflex
Trigeminal stimulation feedback no the uveal tract in uveitis
See in corneal ulceration
What to use with complicated corneal ulcers
Antibiotics with good gram -ve cover which is bacteriocidal
Anticollagenase if evidence of melting ulcer
Atropine and NSAIDs
What mightmultifocal white epithelial opacities on a horse cornea be a sign of
Equine herpes virus keratitis due to EHV-2
What treatment do we use for EHV-2 keratitis
Topical antivirls e.g gangiclovir
What is eosinophilic keratitis
Immune mediated disease
treat with topical corticosteroids
Where in the eye might we get squamous cell carcinoma
All components of exterior globe/eyelids
i.e eyelids, conjunctiva, cornea, orbit
What is chorioretinal scarring
Depigmentation of the fundus related to previous inflammation e.g from equine recurent uveitis
May present as bullet holes or butterfly lesions
What is anterior vs posterior vs panuvieitis
i) Anterior uveitis: iris, ciliary body, anterior chamber
ii) Posterior uveitis: vitreous, retina, choroid
iii) Panuveitis: all areas of uveal tract affected
Treatment of equine uveitis
Topical corticosteroids, NSAIDs, systemic NSAIDs
Atropine
May implant cyclosporin implants under choroid in recurrent cases
WHat is the end stage appearance of uveitis
small shrunken globe = phthisis bulbi
What is phthisis bulbi
Small shrunken bulb due to end stage uveitis
What is the most common cause of blindness in the horse
Equine recurrent uveitis
What is the aetiology of equine recurrent uveitis
Immune mediated
ASsociation with leptospira infection, with systemic illness
Acute stage signs of uveitis
pain, lacrimation, blephrospasm, eyelid oedema, perilimbal corneal vascularisation, mioisis, inflammatory debris in anterior chamber (fibrin, pus i.e hypopyon), vitritis (clouding of vitreous), hypotony
Chronic stage signs of uveitis
less pain, darkened iris, corneal oedema, adhesions b/w iris and lens (= posterior synechiae), corpora nigra atrophy, corneal mineralisation (calcific band keratopathy), cataract, lens luxation/subluxation (fibres that hold it in place degrade), chorioretinal scarring, glaucoma
What cause of keratitis typically has a frosted appereance
Fungal keratitis
What can present as unilateral corneal odema, stromal fibrovasculariation
Immune medaited keratitis
Treat with corticosteroids and cyclosporin
