Equine Diseases Ophthalmology

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