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what is the horse’s range of vision
350 degrees
285 monocular
65 degree binocular
where are the blind spots
cone extending 3-4 inches in front
from back to head to behind horse
when looking at a distant object the horse will ________
when looking at a near object the horse will _______
raise its head
lower its head
what is a horse’s acuity
20/30
do horses have good or poor accommodation (changing lens shape to focus)
poor
why can horses see better at night than humans
they have more rods
T/F Horses have trouble moving from a light area to a dark area
true
what colors do horses see?
only blue and green
explain how light enters the eye
clear cornea allows light in > light passes through aqueous humor in the anterior chamber > iris contracts, dilating pupil letting in more light > light travels through lens which focuses it onto retina > passes through vitreous humor into posterior chamber > light hits retina > optic nerve sends signals to brain
what is a anatomical feature horses have that other animals do not
corpora nigra: dark structure attached to the pupil
corneal abrasions are
partial thickness injuries that do not enter the anterior chamber
corneal lacerations are
full thickness injuries that often allow the iris to protrude through them
have to be saved with surgery
corneal ulcers are
a cornea issue that very in severity from mild to severe so much so that the eye may have to be removed
what is keratitis
inflammation of the cornea
are lid lacerations a cosmetic issue?
No
they need intact lids to distribute tear film
All lid lacerations should be
surgically repaired
what is conjunctivitis
inflammation of the conjunctiva
appears swollen and hyperemic
what is equine recurrent uveitis
repeated inflammation of the uveal tract
causes pain, swelling, blepharospasm (squinting), and epiphora (excess tearing)
what is the uveal tract composed of
choroid: tissue layer filled with blood vessels
ciliary body: ring of muscle tissue that changes the size of the pupil and the shape of the lens
iris: colored part of the eye
with equine recurrent uveitis, which patients get it most commonly
appaloosas and horses that have had leptospirosis
what are the three most common ocular tumors
squamous cell carcinoma
melanoma
sarcoid
what will we take in from our exam at a distance
general attitude
symmetry
alertness
comfort level
during the exam, what tests do we do to assess function of the eye
PLR: direct and consensual (the eye you shine the light in is the direct and the opposite pupil constricting is the consensual or indirect)
Menace response: moving a hand towards their eye slowly
Palpebral response: tapping the medial and lateral canthus
who is the menace response absent in?
neonates
what are we looking at during the fundic exam with the aphthalmoscope
retina
tapetum
optic disk
the pupil is dilated with tropicamide and the retina, tapetum, and optic disk are looked at
where do we perform nerve blocks
auriculopalpebral (motor)
supraorbital (sensory)
what stains do we perform
fluorescein: shows us disruption of corneal epithelium. the stain will take up in the stroma
rose bengal: superficial epithelial disruptions
what is the important to know about the nasolacrimal duct
two lacrimal puncta
one nasal puncta
fluorescein in eye should empty into the nostril
horses usually tend to get blockages that may need to be flushed with saline
equipment for eye exam
drugs, needle, and syringe for sedation and blocking
fluorescein strips
tropicamide
eye wash
direct ophthalmoscope
transilluminator
indirect ophthalmoscopy lens
panoptic ophthalmoscope
how to place solutions in the eye
place your hand either above or below their eye and keep it on the horse. if they move you move with them
ointments are placed
inside the slightly rolled out lower lid
what is a subpalpebral lavage system useful for
administering medication to the eye without having to sedate the animal and get close to the eye
subpalpebral lavage kit
long tubing attached to sharp metal trocar
horse is sedated
lid is blocked and cornea anesthetized with proparacaine
plastic tube is placed under the eyelid to guard it
trocar is inserted through the tube and pushed through the eyelid
round disk is at the end of the tube and to make sure nothing rubs the cornea
tube is secured with tape then braided into the mane
end of tubing has catheter that is taped to tongue depressor and injection cap is added to administer medications
what are some things we need to tell clients
help clients learn how horse vision affects behavior
teach owners proper medication techniques
eye problems are emergencies
Note
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