9, 10 - posterior segment Flashcards
what tunic is the outer layer of the eye?
fibrous tunic
what makes up the fibrous tunic?
cornea
sclera
what tunic is the middle tunic?
vascular tuinc
what makes up the vascular tunic?
choriod, ciliary body, iris / uvea
what is the inner layer of the eye?
neural tunic
what makes up the neural tunic?
neural retina and retinal pigmented epithelium
what are the 2 humors of the eye?
where is each loc?
- aqueous humor: occupies the anterior chamber
- vitreous humor: occupies the posterior cavity / segment
the retina has ___ distinct layers
10
what is the basic pathway of signal transmission through the retina?
light hits the retinal pigmented epithelial cells -> signal sent to photoreceptors -> signal sent to bipolar cells -> synapse on ganglion cells -> go to optic N head and into brain
the posterior portion of the globe has 2 very specialized regions. what are they?
optic N
tapetum lucidum
where is the tapetum lucidum loc in most animals?
what animals are exceptions?
dorsal fundus
exceptions: camelids primates swine squirrels birds some marsupials
how does the tapetum lucidum differ in carnivores vs ungulates?
cellular in carnivores
fibrous in ungulates
what shape is the tapetum lucidum?
triangular
t/f
fundoscopy is the examination of the retina
false
fundoscopy is a composite of the posterior segment structures: the retina, choriod (and tapetum lucidum +/-) and sclera
what structure is the posterior component of the fibrous tunic?
the sclera
what is the deepest layer of the fundus?
- the outermost layer of the globe
- furthest layer from the viewer
the sclera
what color is the sclera?
white or pale pink
what is the lamina cribrosa?
where is it loc?
area considered to be the seed - allows the optic N fibers to go thru the globe and out into the orbit
loc in the sclera
what is the choriod?
posterior component of the uvea or vascular tunic
vascualar structure
describe the blood vessels of the choroid?
radially-oriented w minimal branching
appear pink-to-orange
that is the tapetum?
what structure is the tapetum part of ?
a mirror like reflective layer
a component of the choroid
what molecule is a part of the tapetum in dogs?
cats?
dogs - zinc cysteine
cats - riboflavin
what shape and location is the tapetum?
often triangular
loc in dorsal fundus
t/f
the tapetum is present in all animals
false
what are the components of the retina?
- retinal pigmented epithelium (RPE)
- neural retinal
- retinal vasculature
what are the 2 regions of the retinal pigmented epithelium and where are they loc?
pigmented: over non-tapetal region [variable]
non-pigmented: over the tapetum
where is the neural retina loc?
appearance?
lies over the retinal pigmented epithelium
it is transparent [unless detached]
describe the retinal vasculature.
how does it differ btwn dogs and cats?
branching, dark blood vessels
dogs: anastomose in a ring on the optic disc
cats: end/begin at the edge of the optic disc
what Diagnositcs are done for posterior segment examination?
- visual testing
- ophthalmoscopy
- electrodiagnostics
- other / ancillary
what diagnostics are important for visual / behavioral testing?
menace response
tracking behavior
maze test
how is tracking behavior tested?
see if patient’s eyes follow a dropped cotton ball
what are 2 types of maze tests?
why is each important?
scotopic - done in dim light
photopic - done in ambient light
*helps to distinguish rod and cone dysfunction
t/f
the menace response is present in all animals
false
NOT in very young animals b/c learned response
what animals are considered precocial? altricial?
significance?
precocial: develop later => puppy/kitten around 4 weeks
altricial: develop early => foal around 2 wks and lamb/goat about 8-14 days
what is the pathway of the menace response?
afferent: optic N -> thalamus (lateral geniculate nucleus) -> visual cortex in occipital lobe -> perception in frontal cortex
efferent: frontal cortex -> cerebellum -> facial N -> blink response
what does the dazzle reflex test?
- sub cortical reflex
- tests a good portion of visual pathways
what does the pupillary light reflex (PLR) test?
is it present in retinal dysfunction?
- reflex through the mid brain
- may be present w significant retinal dysfunction
is the dazzle reflex cortical or sub cortical?
sub cortical
what is the pathway of the pupillary light reflex?
optic N -> optic chiasm -> synapse bilaterally on neurons loc in pre tectal nuc -> axons synapse on parasympathetic nuclei of ocular motor N -> most cross over and synapse on the contra lateral ciliary para sympathetic nerves / ganglia
what do you need for a good fundus exam?
bright focal light source
patient at eye level
dark room
magnification (lens)
mydriasis!!! to see entire fundus
what drugs can be used to cause mydriasis ?
what are the important properties of each?
atropine - long acting and slow onset
tropicamide - short acting and fast onset
describe direct ophthalmoscopy.
upright image high magnification easy to use equipment readily available shorter working distance narrow field of view
what do different settings on the ophthalmoscope mean?
setting depends on location of lesion in the eye
what do the following settings on the direct ophthalmoscoope allow viewing of?
0 D
+8D
+12D
+20D
0 = fundus 8 = posterior lens 12 = anterior lens 20 = cornea lens
describe view with indirect ophthalmoscopy?
inverted image [upside down and backwards] wider field of view stereopsis requires practice to master low magnification than direct
for indirect ophthalmoscopy, a lower number magnification means _____ (higher/lower) magnification?
higher magnification
what does electroretinograpy measure?
retinal photoreceptor function
rods and cones
what is the classic sign seen with ocular u/s to indicate retinal detachment?
“seagull sign”
what does ocular u/s allow visualization of?
- the retina when lens or cornea is opaque
- the orbital portion of the optic nerve
what does CT or MRI reveal?
orbital portion of the optic nerve
describe a normal canine fundus?
triangluar in shape, vessels anastomose over the optic N head, myelination of optic N head
can look yellow / yellow
what does a normal canine fundus look like if the dog is blue eyed?
atapetal - lack pigment - can see retinal vessels
dark red optic nerve head
orange/red choroidal vessels loc behind the retina
what does the tapetum of the puppy look like
blue before 4 months old b/c immature
what does cat fundus look like?
round
vessels stop at end of optic nerve; do NOT anastomose over the optic N head
domestic animals are better adapted for nocturnal or day vision?
nocturnal
what Hertz of flickering light are animals adapted to see?
70-80 Hertz
why is night vision improved in animals?
large pupil
tepetum lucidum is reflective
more rod photoreceptors
rods detect light in ____ conditions and _____ detect light in bright conditions
dim
cones
animals can see some colors but they are more muted than colors humans can see. why?
b/c they have fewer cone receptors
carnivores have good predatory vision b/c their eyes are set more _______ in the head so they have enhanced _____ vision
rostro laterally
binocular
the eyes of prey animals are set more ______ on the head, giving them better ______ vision or panoramic views
laterally
monocular
what type of color blind are horses compared to humans?
how many cones to horses have?
what hues can they see?
orange and light blue color blind
horses have 2 cones - blue and red/green
can see yellow and blue hues
NO intermediate colors
dogs are dichromat because they have fewer _____
these structures allow them to see which colors?
as a result, what type of color blind are they when compared to human vision?
cones
blue and yellow-green cones
red/green color blind
what is the approximate visual acuity of dogs and cats compared to humans?
dogs: 20/70
cats: 20/100
what does a horse fundus look like?
parangiotic -> few retinal vessels, therefore more opaque
what does a bovine fundus look like?
darker optic nerve head
dorsal retinal vessels tend to intertwine like twizzlers
vessels are present on the fundus
what does a rabbit fundus look like?
marangiotic fundus - vessels and nerves follow a horizontal line
what is uniique about an avian fundus?
black structure present - the pectin
*fxns as a nutrient source for optic nerve head
how can the reflectivity of the fundus be altered?
hyper reflective
hypo reflective
what are 2 circumstances under which hyper reflectivity occurs in the fundus?
absent tapetum
retinal thinning d/t degeneration
how does hypo reflectivitty occur in the fundus?
increased retinal thickness
cells or fluid
what pathology occurs in the vessels of the fundus?
3 conditions
- vascular attenuation
- vascular tortuosity
- hemorrhage
what is vascular attenuation?
fewer vessels and smaller vessels
what is vascular tortuosity?
vessels become more engorged / coiled than normal
t/f
retinal hemorrhage is usually a 1* condition
false
usually is a 2* condition
what are some common causes of retinal hemorrhage?
hypertension hyper viscosity coagulopathy chorioretinitis [tick borne] diabetes 2* to trauma or sx
what is retinal detachment?
neurosensory retina separation from the underlying retinal pigmented epithelium
what are signs of retinal detachment?
sub retinal fluid accumulation
retinal tears [rhegmatogenous]
what type of fluid may be present in sub retinal fluid accumulation?
serous
exudative
hemorrhagic
where does the retina attach to the optic nerve?
at the periphery
what are some rule outs associated with retinal detachment?
hypertension hyperviscosity spontaneous/idiopathic coagulopathy vitreous dz chorioretinitis 2* to trauma or sx
under what circumstances might retinal detachment occur spontaneously?
if the 1* cause is addressed
what is the prognosis of retinal detachment?
guarded for vision
70% with Sx
how is retinal detachment treated?
correct 1* cause
Sx
what breeds are predisposed to developmental retinal dysplasia?
cocker spaniel
english springer spaniel
labrador
what etiologies may lead to retinal dysplasia?
intra uterine infections [viral]
toxicoses
radiation
nutrition
abnormal retinal folding may occur as a result of what?
retinal dysplasia
what is the etiology of collie eye anomaly?
inherited
developmental
what are the pathognomonic lesions for collie eye anomaly?
- choroidal hypoplasia
- posterior segment coloboma
- retinal detachment
what is PRA or PRD?
etiology?
progressive retinal atrophy or degeneration
inherited
what occurs during PRA/D?
photoreceptor degeneration
what diagnostic test reveals abnormalities of PRA/D before vision changes occur?
ERG
which photoreceptors are affected in PRA/D?
what type of blindness?
rods then cones - night blindness occurs first
eventually total blindness
PRA/D leads to what 2* condition?
cataracts
what is SARD?
etiology?
sudden acquired retinal degeneration - photo receptors sudden degeneration
unknown etiology
typical signalment of SARD?
middle aged FM dog MC
what systemic abnormalities occur with SARD?
- resemble cushings dz
- PU/PD, weight gain, polyphagie
- elevated ALT, ALP
what is etiology and common presentation of feline retinal degeneration?
often occurs 2* to what condition?
idiopathic cause
inherited: abyssinian and persian breeds
2* to retinal detachment / retachment
feline retinal degeneration may occur d/t toxin of what drug?
enrofloxacin
what does taurine deficiency cause in the eye?
in the heart?
irreversible retinal degeneration
reversible dilated cardiomyopathy
what is chorioretinitis?
what is the origin?
inflammation of the retina and choriod
origin is choroid
what 2 types of chorioretinits are there?
active dz
inactive dz
what is seen in active chorioretinitis?
hypo reflective pigmentation variable INDISTINCT margins to lesions hemorrhage raised
what is seen in inactive dz?
hyper reflective
pigmentation
WELL DEFINED margins
what are causes of canine chorioretinitis?
viral - distemper rickettsial dz - RMSF, e. canis deep mycotic dz neoplasia immune mediated protozoal - toxo, neospora idiopathic
what are causes of feline chorioretinitis?
viral - FeLV, FIV, FIP deep mycotic dz neoplasia immune mediated hypertension toxo idiopathic
tx of chorioretinitis?
- address underlying cause
- systemic corticosteroid - controversial
- topical corticosteroid - IF ANTERIOR SEGMEND INFLAMMATION b/c do NOT reach the posterior segment
neoplasia of the fundus:
common?
prognosis?
Tx?
uncommon
1* or 2*
guarded to poor prognosis
Tx: enucleation, laser
2 developmental dzz of optic N that lead to small optic disk:
- micropapilla
- optic N hypoplasia
2 developmental dzz of optic N:
small optic disc
optic N coloboma
what is optic N coloboma?
hole in optic disc
what are 3 acquired dzz of the optic N?
papilledema
optic neuritis
glaucoma
with which dz of the optic N can the animal remain visual?
micropapilla
which dz of the optic N is animal usually blind?
optic N hypoplasia
what does papilledema look like?
- swelling of the optic N d/t inc intra cranial pressure
- distinct margins on disc
- raised vessels at edge
etiology of papilledema?
neoplasia
hydrocephalus
head trauma
what is optic neuritis?
inflammation of optic N
is animal blind or visual in case of optic neuritis?
blind
presentation of optic neuritis?
optic disc is raised
fuzzy, indistinct disc margins
hemorrhage on or around optic N head
bilateral blindness w dilated pupils
etiologies of optic neuritis?
intra cranial causes
see ddx for chorioretinitis
Tx of optic neuritis?
supportive care
anti inflammatories
immunosuppression - but risky if infectious etiology
diagnostics for optic neuritis?
comparable thorough work up as with uveitis
CT scan
CSF tap
good referrel
what is the pathology of the optic nerve that leads to glaucoma?
ganglion cell destruction - loss of optic N axons
what is appearance of optic N in glaucoma?
optic N is “cupped” or depressed - optic N head more prominent b/c axons are lost
prognosis of glaucoma from optic N pathology?
poor for return of vision once ganglion cell loss occurs
what are 2 dzz of the vitreous?
persistent hyaloid
vitreous degeneration
what is etiology of persistent hyaloid?
PHPV / PHTVL
developmental - persistant tunica vasculosis
what are 2 causes of vitreous degeneration?
asteroid hyalosis
synersis
what is synersis of vitreous?
liquefaction
what is asteroid hyalosis?
calcium phospholipid deposits in the vitreous
what pathology of the eye looks like a snow globe?
the particulates in the eye move opposite the head motion
vitreous degeneration
how might an orbital mass affect the posterior segment?
orbital mass may push eye out and cause elevation
