Equine ophthalmology Flashcards
(46 cards)
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
