13 - equine - pearce Flashcards
do horses have better monocular vision or binocular vision?
what is the approximation of how much of each view the horse has?
better monocular vision -> 146*
binocular vision -> 65*
what is the total visual panoramic field of the horse (degrees), btwn both monocular field and bonocular field?
350*
where are blind spots in horse?
right in front of eyes and below chin
from behind ears to directly behind butt
t/f
loss of one eye does not significantly effect a horse’s ability to function as it did with both eyes
false
significantly effects horse -> do NOT tell client the horse will be fine as it was before b/c this may set you up for legal problems
horse can live comfortably in the right environment but it will not function as it did before
one eyed horse at a disadvantage and may be more dangerous b/c of this handicapped -> make owner aware
how many cones do horses have?
what colors can horse see?
what type of color blind are horses?
2 cones -> blue and red-green
see 2 basic hues -> yellow and blue; NO intermediate colors
“orange, red and light blue color blind”
basic needs for an ophthalmic exam in horse?
bright, focal light source
dark environment
magnification
same as with other species
is indirect or direct ophthalmoscopy recommended?
why?
indirect
better view of eye
direct is limited to mostly seeing the optic nerve head
what is needed for an indirect ophthalmoscopy exam in horse?
light source
16 Diopter lens
what size diopter lens for dog?
horse?
16 for horse
28 for dog
how to assess vision in horse?
what does pearce think is the best way?
vision directed behavior in stall
tracking
menace response
*best: vision directed behvaior
t/f
a good eye exam on a horse does not need sedation
false
what drugs are used to sedate a horse during eye exam?
xylazine
detomidine
what logistical things are needed for good eye exam of horse?
restraint - stocks, twitch
sedation
topical anesthesia
nerve block
what topical anesthetic agent is used MC?
proparacaine
what motor nerve block is necessary for exam?
auriculopalpabral nerve block
what does the auriculopalpebral nerve block block?
what muscle is paralyzed?
what motion of the horse?
auriculopalpebral branch of the facial nerve (CrN 7)
orbucularis oculi M - akinesia of upper eyelid - horse cannot close eyes well
t/f
during the auriculopalpebral nerve block, insert the needle directly into the nerve for most effective block
false
do NOT hit nerve
sub Q injection should be around nerve - then massage the injection site to help with absorption
what drug used for the auriculopalpabral nerve block?
2% lidocaine or 2% mepivacaine
how long does the auriculopalpebral nerve block last?
lasts 1-3 hours
what are landmarks for the auriculopalpebral nerve block?
high point of zygomatic arch
Cd to bony process of frontal bone
Cd to posterior ramus of mandible
N lies on the zygomatic arch
t/f
the auriculopalpebral N block blocks both motor and sensory function
false - only motor
what regional nerve blocks are done to accomplish sensory nerve block?
lacrimal N
zygomatic N
frontal N
infratrochlear N
when are sensory blocks done?
during some exams
for eyelid laceration repair
3rd eyelid surgery
biopsies of periocular area
what is NORMAL intraocular pressure (IOP) in horse?
17-28 mmHg
what is necessary for accurate IOP measurement?
calm animal
avoid pressure on globe / lids
natural, physiologic head position
sedation and lid block
if there is over ____ mmHg pressure difference btwn the eyes, something is wrong
5 mmHg
what are 3 MAJOR equine ophthalmologic issues?
keratitis
SCC
equine recurrent uveitis
what type of infection are horses prone to in their cornea?
fungal
presentation of an acute superficial corneal ulceration?
- distinct borders of epithelium lost
- corneal edema
- absence of cellular infiltrate or malacia of the stroma
Tx of superficial corneal ulceration?
ID underlying cause
Px 2* bacT infection
atropine
antifungal***
frequency of abx for Tx of acute superficial corneal ulceration?
Tab QID for a week
what is fxn of atropine to Tx acute superficial corneal ulceration?
pupillary dilation
what is a concern for using atropine in horses?
what is max use to lower risk of this occurring?
gut stasis / ileus may occur
2x day use MAX - more than that inc risk of ileus
how to Dx melting or deep stromal ulceration?
corneal cytology and corneal culture
*use sedation and lid block to scrape cornea, NOT eyelids b/c different flora there
when should a corneal ulcer be referred?
- over 1/2 stromal depth
- rapidly progressive or melting
- no neovascular response
- perforated and actively leaking
when is medical management used in tx of corneal ulceration?
until Sx can be performed
if owner cannot afford surgery
t/f
if managed carefully, a deep corneal ulcer can be treated at home with the clients
why or why not?
false
ideal situation is a hospital where it can be medicated every few hours
what can be placed inferomedially in the horse’s eye to aid in Tx equine eye dzz?
sub palpebral lavage tube
what are 2 MC fungal corneal pathogens?
filamentous fungi - molds
Fusarium spp
Aspergillus spp
t/f
equine ulcerative keratomycosis is a sight threatening dz, even when well managed and treated appropriately
true
describe the pathology of equine ulcerative keratomycosis
presence of fungi
epithelial barrier disrupted -> inoculation of corneal stroma
how to dx eq ulcerative keratomycosis?
cytology
culture
tx of equine ulcerative keratomycosis?
standard ulcer
topical antifungal
surgery - often required
what are 3 Triazoles used to Tx fungal infections in horse?
fluconazole
itraconazole
voriconazole
whatt are 2 imidazoles used to Tx fungal infections?
miconazole
ketoconazole
what are 3 polyenes used to Tx fungal infections?
natamycin
nystatin
amphotericin B
what drug is dr perace’s favorite to treat fungal infections associated with a superficial ulcer?
silver sulfadiaziazine
what 2 fungal drugs are compounded?
itraconazole
miconazole
what 2 fungal drugs are available at a human pharmacy?
voriconazole
natamycin
which fungal drug is used off label for equine corneal dz but is well documented and proven to be efficacious?
voriconazole
in a corneal abscess, is the epithelium intact or broken?
intact
in corneal stromal abscess, what does the corneal stroma look like?
white - yellow stromal infiltrate
t/f
a fluorescein stain is positive in the corneal stromal abscess
false
it is negative - epithelium is intact
what is MC sequelae to corneal stromal abscess?
2* uveitis
t/f
Tx of corneal stromal abscesses is simple and very rapid once initiated
false
long term treatment is needed
tissue heals once it is vascularized
how are corneal stromal abscesses treated?
- topical abx every 4-6 hours
- topical atropine to effect
- topical antifungal
- systemic NSAIDs
- maybe systemic abx and anti fungals
what abx are used to Tx corneal stromal abscesses?
why is abx selection very important in these cases?
fluroquinolones and chloramphenicol used often
abx must get thru the intact epithelium
t/f
common Tx for stromal abscess is Sx excision and graft
false
it is an option but is not done routinely - is only done if response to medical Tx is poor and Sx is required
MC tumor of the eye and eyelids in equine?
*also the 2nd MC tumor in horse overall
SCC
what structure does the SCC occur on?
3rd eyelid
conjunctiva
cornea
eyelids
breed predilection to SCC?
draft breeds
appaloosa
color dilute horses
describe behavior of SCC typically
slow to met and most will NOT (6-15%)
but locally invasive
if left untreated, what will occur in cases of SCC?
local invasion
t/f
surgery alone is best and most effective Tx for SCC
false
Sx alone will lead to 40-60% recurrence of SCC
Tx of SCC?
Sx and adjunct therapy
best Px for SCC?
UV protection
what is MC skin tumor in horses?
sarcoid
sarcoid tumors are bengign or malignant?
benign - fibrous tissue
what specific etiology is associated with development of equine sarcoids?
bovine papilloma virus
not strong direct link but DNA isolated in lesions via PCR
what triggers sarcoids to develop?
trauma and biopsy - handle them carefully
in addition to around the eye, where do sarcoids also occur commonly?
around legs
what adjunct therapies are used to Tx SCC and sarcoids?
freezing radiation hyperthermia immunotherapy chemotherapy photodynamic therapy
what breeds are at high risk for equine recurrent uveitis?
Appaloosa
European warmblood
draft breeds
t/f
equine recurrent uveitis is a widspread dz but is easily treatable
false
is difficult to treat and frustrating…
what is the common dz course of ERU?
initial uveitis episode
periodic uveitis episodes
chronic and recurrent
what are acute signs of ERU?
aqueous flare keratic precipitates keratitis vitritis chorioretinitis
c/s of chronic ERU
cataracts synechia iris hyperpigmentation corpora nigra atrophy glaucoma blindness phthisis bulbi => end stage
what lesions are seen on the fundus in cases of ERU?
retinal detachment
bird-shot retinopathy
butterfly lesion
how is leptospira linked to ERU cases?
when horse is infected w lepto bacT, the body develops immune response to the lepto Ag -> eye tissue is similar to the lepto Ag so the body may attack its own eye, after a lepto infection -> ERU cascade begins
what parasitic infection may lead to ERU?
oncocerca cervivcalis worm
medical Tx options of ERU?
immunosuppressants - systemic corticosteroids
anti inflammatory drugs - systemic and topical NSAIDs
dilating agent
abx
vax
sx tx options of ERU?
cyclosporin implants
how effective are cyclosporine implants to Tx ERU?
how does this outcome compare with patients who did not get an implant?
good - for early cases and horses who are visual
CSA has good penetration of ocular tissue and inhibits lepto
15% became blind, but much more than 15% who did not get implant became blind
t/f
no matter what we do, most ERU horses become blind
true
56% of ERU horses in 2 years will be blind
