Flashcards in lab: MDB - pearce Deck (125):
overall importance of ophthalmic exams?
- dzz of ocular support unit affect the eye, the organ that you can look inside of on an exam
- vessels and Nn are visible in the eye
- the anterior chamber is a direct look at "an interstitial space"
- eye shows corroborative evidence of sys dz
- ocular path can help narrow the differential dx and help prioritize dx testing
- vision is important to dogs and their owners
- if you have a land shark, lids are safer than lips :)
general approach to exam of the eye:
- front to back
- consider relationships btwn anatomy of the tunics / layers and dzz
what are the 3 tunics of the eye?
- fibrous tunic
- vascular tunic
- neural tunic
what comprises the fibrous tunic?
cornea and sclera
what comprises the vascular tunic
the uveal tract
what comprises the uveal tract?
what makes up the neural tunic?
what makes up the internal optical media?
what are the goals of ophthalmology treatment / patient care?
overall diagnostic approach to the eye?
- ID problems
- minimum ophthalmic database
- clin dx
- diagnostic plan
what are the aspects of the minimum ophthalmic database?
- neurophthalmic exam
- schirmer tear test
- fluorescein stain
- complete ophthalmic exam
- additional diagnostics
important questions to ask during history regarding what signs made the owner think the dog had an eye problem?
how does dog see with:
- different environments
- onest/duration of issue
- relatives w ocular problems?
in terms of comfort, what are some questions to ask during history?
general questions to ask while taking the patient history?
- how long has client noticed problem?
- any dec in activity or appetite?
- if animal is blind, how long has the blindness been present?
- ask about medication - what meds, how often, when was last dose
the pupillary light reflex (PLR) is an important test of vision
NOT a vision test b/c it does NOT require cortical perception of vision
what Cranial Nerves (CrNn) does PLR require?
CrNn 2 (afferent) and 3 (efferent)
what region of the brain does the PLR utilize?
with significant retinal dysfunction, the PLR will not be present
the PLR may be present with significant retinal dysfunction
PLR will be absent with cortical blindless
PLR is NOT a test of vision and will be present with cortical blindness - cortical perception of vision NOT required for PLR
during a PLR test, what is the response called that occurs in the eye with direct light simulation?
during a PLR test, what is the response called that occurs in the opposite eye - the eye that is NOT receiving light stimulation?
what is the pathway of PLR?
direct light stimulation -> retina and optic nerve (CrN 2) -> optic chiasm -> pupillo-motor fibers -> PS fibers, oculomotor N (CrN3) -> indirect or consensual PLR
how is the PLR altered in an excited or stressed dog?
it is decreased
how does iris atrophy affect PLR?
decreased or absent PLR
does age affect PLR?
yes - b/c age affects sphincter or muscle so PLR may be dec
what is the dazzle reflex?
intense blink response that occurs with light stimulation
the dazzle refllex is a good test of vision
the dazzle reflex does NOT require the visual cortex
the dazzle reflex is a reflex of what region of the brain?
what does the dazzle reflex look like?
light stimulus causes an involuntary blink
what CrNn does the dazzle reflex test?
CrNn 2 and 7
the dazzle reflex is one of the first reflexes to go in an animal that is deteriorating.
the dazzle reflex is one of the last things to go
is the dazzle reflex present with significant retinal dysfunction?
yes, it may or may not be preset with significant retinal dysfunction
what is the pathway for the dazzle reflex?
light stimulation -> retina and optic N (CrN 2) -> mid brain (most likely) -> facial N (CrN 7)
what tests evaluate vision in animals?
placing reaction (cats)
what is the placing reaction in cats?
when initially removed from carrier and placed on table, their front paws should reach down for the table
what CrNn does the menace response evaluate?
CrNn 2 (afferent) and 7 (efferent)
the menace response is a learned response, therefore, is not present in young animals
around what age does a puppy develop a menace response?
14 wks old
how does the menace response differ btwn species that are precocious and species that are altricial?
menace response development occurs earlier in more precocious species
ex) horse - develops w/in 24 hours vs puppy - develops w/in 14 weeks
what are the vibrisa?
long hairs / eyelashes above the eyes
an important part of eliciting the menace response is to create air currents flowing past the animals eyes
do NOT create air currents - that interferes with the menace response b/c the animal responds to the air, and not the 'menace', or your hand
are both eyes evaluated together or is each eye evaluated separately during the menace response?
each eye is tested separately
what is the neural pathway of the menace response?
stimulus -> retina and optic N [CrN 2] -> thalamus -> occipital cortex -> frontal cortex -> cerebellum -> facial N [CrN 7) -> blink
how do tracking behavior tests work? what is a simple way, in a typical exam room, to evaluate his?
follow the animal's ability to track an object / stimulus
drop a cotton ball and the animal's eyes should follow it - however, some cats will not participate even if they are visual
how is maze testing carried out?
place objects randomly in front of the animal and see if they are able to navigate around them
may also dim light first to evaluate night vission
night vision issues often occur with what type of dzz?
what should be evaluated during a maze test?
speed of navigation
what is the maze called when conducted in ambient light?
and in dim light?
ambient: photopic maze
dim: scotopic maze
what is the palpebral reflex?
the blink reflex elicited when the peri ocular area is touched
what CrNn does the palpebral reflex evaluate?
which is afferent and which is efferent?
afferent: CrN 5 [ophthalmic N]
efferent: CrN 7
what are the branches of CrN 5?
what region does each branch innervate?
maxillary Br: lateral canthus
ophthalmic Br: medial canthus
mandibular Br: base of ear
what is the corneal reflex?
the blink response that is evaluated when the cornea is touched with a cotton wisp
what CrNn are utilized during the corneal reflex?
which is afferent and which is efferent?
CrN 5 - afferent
CrN 7 - efferent
what does the corneal reflex evaluate specifically?
what must NOT occur before the corneal reflex exam in order for the results to be diagnostic?
topical anesthetic [proparacaine] must NOT be given before the corneal reflex is evaluated
what is the common name for the oculocephalic reflex?
doll's eye reflex
how is the oculocephalic reflex evaluated?
what is normal and abnormal?
move head up/down and right/left
normal: eyes should move from side to side or up/down as the head is manipulated
abnormal: no eye movement
in what direction does the fast phase nystagmus occur?
in the direction of head movement
what system/region if the brain is evaluated with the doll's eye reflex test?
the vestibular system
what CrNn are evaluated during the doll's eye reflex test?
CrN 3 - oculomotor
CrN 8 - vestibulocochlear
CrN 6 - abducens
when localizing neurophthalmic lesions, which 2 response tests evaluate for afferent function of CrN 2?
menace response and PLR
when localizing neurophthalmic lesions, which 2 response tests evaluate for efferent function of CrN 7?
menace response and palpebral response
what does the Schirmer tear test evaluate?
basal tear production
stimulated tear production
what the normal measure from the Schirmer tear test?
over 15mm / 60s
if btwn 10 and 15 mm / 60 seconds is measured from a Schirmer tear test, what condition is suspected?
what value confirms this condition?
less than 10 mm / 60 seconds
what is the correct placement of the Schirmer tear test strips?
in the inferior fornix of the eye, central to lateral 1/3 of lower lid
must touch cornea in order to stimulate eye properly to produce tears
if the Schirmer tear test strip falls out of the patient's eye before the test is complete, how long must you wait until you run the test again?
why is this important?
wait 20 minutes
the lacrimal lake will have emptied and needs this time to refill
what 2 tests must be conducted prior to topical anesthetic administration?
the corneal reflex and the Schirmer tear test
why must anesthetic be applied after the Schirmer tear test and never before?
the anesthetic agent drops will add moisture to the eye, altering the tear test evaluation
AND stimulated tear test could not be measured if the cornea is desensitized
how is a fluorescent stain test carried out?
moisten strip with eyewash and apply 1 drop to the eye
what does a fluorescent stain test evaluate?
evaluates for presence of epithelial defects
if there is an area of fluorescent stain in the eye after the test, what does that mean?
positive test - indicates a corneal defect in the epithelium - the epithelium on the surface of the eye has a defect so that the dye entered the corneal stroma
what tissue does the fluorecein stain adhere to?
due to what what property of the tissue and the stain?
the stain is hydrophilic, and so is the corneal stroma, so they adhere to each other
what does a negative fluorescein stain test look like?
no dye uptake in the eye tissue
the die is hydrophilic and the epithelium on the surface of the eye is hydrophobic - so they do not adhere to each other
what if there is a donut like appearance of the uptake of fluorescein dye in the eye?
why does the stain appear this way?
there is a defect that goes through the epithelium, into the corneal stroma, and all the way down to the endothelium [Descemet's membrane]
the stain adheres to the corneal stroma, located beneath the surface epithelium, but NOT to the endothelium, which is located under the corneal stroma - this is hydrophobic, like the epithelium so does not take dye
how is tonometry utilized?
digital pressure reading on eyes
when should intra ocular pressure be measured?
every red eye with an intact cornea and sclera
genetic reasons - glaucoma risk
part of minimum ophthalmic database
monitoring uveitis cases
monitoring ophthalmic surgery cases
when should intra ocular pressure NOT be measured?
if the eye is perforated or if there is perforation potential in the eye
deep stromal or melting ulcers
why should IOP of uveitis patients be measured?
b/c inflammation in the eye over time can lead to glaucome
what is normal intraocular pressure in the dog? cat? horse?
dog: 12-15 mmHg
cat: 12-27 mmHg
horse: 17-28 mmHg
how to obtain an accurate IOP measurement?
animal must be calm
avoid pressure to globe and lids - hold the orbital rim - or results may be altered
when measuring IOP, you are more likely to get abnormally high measurements, so if you take multiple measurements, use the lowest reading as most accurate
there should be less than ___ mmHg of IOP difference between the 2 eyes?
what are 3 methods of tonometry?
what are pros to using Schiotz tonometry?
- accurate w practice
what are cons to using Schiotz tonometry?
- inconvenient in some spp
- req practice
- req horizontal cornea
- difficult to clean
- need conversion chart
- affected by corneal dz
pros to using applanation and rebound tonometry?
- convenient for small corneas
- simple to use
- vertical cornea ok
- easy to clean
cons to using applanation and rebound tonometry?
- may need some servicing [minimal]
what are some easy mistakes to make to keep in mind and avoid, while taking IOP reading?
pressure on neck [none from you or the leash/collar]
head position [should be physiologic position]
pressure on globe from improper lid retraction
what is the protocol for using aplanation tonometry?
- topical anesthesia
- force to flatten corneal surface, gentle touch
- accurate w many corneal abnormalities
- easy to artificially elevate IOP: brachycephalics esp
- calibrate prior to use or daily
- use readings w coefficient of variation of less than 10% - measure btwn 3-6 readings
- do not make cover too tight or too loose
protocol for rebound tonometry with the tonovet?
- electromagnetically propelled probe --> bounces off cornea
- calibrated for each species by manufacturer (dog/cat, horse, mice)
what additional diagonstics might be recommended beyond the MDB for optho exam?
- corneal cytology [topical anestiesia, gently scrape margin of ulcer with a blade, spatula or brush]
- corneal culture - bacT, fungal, swab margin of ulcer but do NOT touch eyelids
what is the Jones test?
look for fluorescin at nares - to demonstrate an intact NL duct
how to carry out a nasolacrimal flush?
- 5-10 mL syringe w eyewash
- 24 gauge IV catheter w stylette removed
- insert catheter in upper puncta
- flush caniliculi and down NL duct
what is the Seidel test?
- evaluate for perforatioin
- concentrated fluorescein
- look for pale rivulets in fluorescein stain -> aqueous egress through perforation site
during the ophthalmic exam, what does OS mean?
OS = left [sinister] eye
OD = right eye
OU = both eyes
what is the proper restraint for an animal undergoing ophthalmic exam?
- gentle restraint, esp brachycephalics
- pressure at the base of the skull and under the chin
what tools to you need to conduct an ophthalmic exam?
- bright focal light source
- dark environment
- patient at eye level
- anterior segment --> slit lamp, head loupes/transilluminator, otoscope
what is diffuse illumination?
wide beam, low light
what is retroillumination?
what structure in animals' eyes allows this?
illuminate from behind
what is a good reference when deciding if one eye in a patient looks normal?
the patient's other eye
what should you evaluate during the distance examination of the patient?
- is the patient visually guided by behavior?
- facial symmetry?
- symmetry in size / shape of orbit and globe?
- eyelid conformation
upon close examination of patient, what should you initially observe?
- retropulse the globe
- is the patient painful upon opening the mouth?
under what condition should you NOT retropulse the globe?
if there is an ulcer
when holding the light source at a distance from your patient, what should you observe?
- tapetal reflexes: highlight anisocoria and opacities in media
bring the light close to your patient during the exam to observe what?
- direct, oblique and retro illumination
anterior lesion back-lit by light from the tapetum or iris
what is a MAJOR concept when localizing a lesion?
object overlay - anterior structures cover posterior ones
what is one method to determine depth of lesion in the eye?
describe the process
slit beam creates optical cross section of the eye: tear film/cornea, black space (AC), anterior lens capsule, lens (smokey), posterior lens capsule
what is the tyndall effect? when is it seen in the eye?
haze due to effect of colloid suspension, when particulates are illuminated by light
seen in anterior chamber when flare cells are present, often due to uveitis
what is the center axis of rotation of the eye?
the center of the lens
lesions anterior to the center of the lens move in which direction relative to the front of the eye?
in the same direction
lesions posterior to the center of the lens move in what direction as the front of the eye?
in the opposite direction
what are 2 ways to conduce a retinal exam?
indirect ophthalmoscopy [light source and lens] and direct ophthalmoscope
what is ophthalmoscopy or funduscopy?
to look at - examine - the eye
what is essential for a complete funduscopic exam?
mydriasis [dilated pupil]
what short acting, fast onset [10-15 mins] drug can be used to dilate the pupil?
what long acting, slow onset drug can be used to dilate the pupil?
how does direct ophthalmoscopy work?
- upright image
- high magnification
- easy to use
- equipment readily available
- shorter working distance
- narrow field of view -> hard to view entire fundus
what does the setting of the direct ophthalmoscope dictate?
the location of the lesion in the eye you can view
positive means more anterior region of the eye
negative means deeper into the eye
zero is good view of the fundus
what is 0 on the ophthalmoscope mean?
good view of the fundus
what does +8 on the ophthalmoscope mean? +12? +20D?
8 = posterior lens
12 = anterior lens
20 = cornea lens
what does indirect ophthalmoscopy tell you?
- inverted image
- wider field of view
- req practice to master
- low magnification
- can visualize more of a fundus at a time
what is important to keep in mind while using indirect ophthalmoscopy?
- make sure lens is parallel to corneal surface
- metal lens rim towards cornea
- animal should "read writing" on lens rim
- think tube
for indirect ophthalmoscopy, what does 30D lens mean compared to a 40D lens?
30D is higher magnification
40D is lower magnification