Anatomy & Exam Flashcards
What bone make up the canine orbit
1) Lacrimal
2) Zygomatic
3) Frontal
4) Sphenoid
5) Palatine
6) Maxillary
What additional bone makes ip the porcine and primate orbit
ethmoid
What additional bone makes up the equine orbit
temportal bone
T/F: Dogs have bone all the way around their eyes
False- they have an open orbit. nothing holding it in place if the soft tissue structure breaks
What passes through the optic canal
1) Optic Nerve (CN II)
2) Internal ophthalmic artery
What passes through the orbital fissure
1) Oculomotor Nerve (CN III)
2) Trochlear (CN IV)
3) Ophthalmic branch of CN V
4) Abducens (CN VI)
if affected- cavernous sinus syndrome
Refers to deficits in more than one of the cranial nerves III, IV, V, and VI, as they are in close association in this region (floor of of calvarium where they leave the orbital fissure
Cavernous sinus syndrome
With Cavernous Sinus Syndrome, what cranial nerves can be damaged
1) Oculomotor Nerve (CN III)
2) Trochlear (CN IV)
3) Ophthalmic branch of CN V
4) Abducens (CN VI)
all leave the orbital fissure
What opening in the skull is assoiated with cavernous sinus syndrome
orbital fissure
What passes through the rostral alar foramen
Maxillary artery
Maxillary branch of CN V
What muscles open the eyelids
1) Levator palpebrae superioris m. (skeletal)
2) Mullers muscle (smooth muscle under sympathetic control)
A structural muscle that elevates the upper eyelid. It’s innervated by the sympathetic nervous system
Mullers muscle
What muscle closes the eyelids
Orbicularis oculi muscle (skeletal muscle)
A test that used to detect obstruction of the nasolacrimal ducts
Jones Test
What drains tears into the nose
Nasolacrimal duct
What is the function of meibomian glands
produce oily components of the lipid layer of the tear film, with these components being secreted along the margins of the eyelids. The lipid layer of the tear film facilitates smooth blinking and attenuates the evaporation of lacrimal fluid
mucous membrane that lines the eyelids and the globe
produces mucoid portion of tear film
has lymphoid tissue
conjunctiva
What produces the mucoid portion of the tear film
conjunctiva
What produces 65-70% of liquid tears
Lacrimal gland
where is the lacrimal gland located
above the eye
a t-shaped piece of cartilage that produces 30-35% of liquid tears
third eyelids
What is a common site for foreign bodies in the eye?
conjunctival fornix
What extra-ocular muscle rotates the top of eye ventronasally
dorsal oblique
What extra-ocular muscle rotates the bottom of the eye dorso-nasally
ventral oblique
What muscle pulls the eye backwards, not present in humans
Retractor bulbi
What are the three layers that make up the globe
1) Fibrous tunic (cornea and sclera)
2) Vascular tunic (iris, ciliary body, choroid)
3) Nervous tunic (retina and optic nerve)
What 2 structures are a part of the nervous tunic of the globe
1) Retina
2) Optic nerve
What 3 structures are a part of the vascular tunic of the globe
1) Iris
2) Ciliary body
3) Choroid
What 2 structures are a part of the fibrous tunic of the globe
1) Cornea
2) Sclera
Anterior uveitis means inflammation of the
iris and ciliary body
posterior uveitis means inflammation of the
choroid
T/F: Cornea and sclera are made of different materials
False - same collagen, differ on their arrangements
Sclera- opaque collagen
Cornea- fibers perfectly arranged allows light to pass through
What species have cartilaginous plates in their sclera
reptiles and fish
What species have bone in their sclera
birds
the point in the fibrous tunic where the cornea meets the sclera
limbus
Is fluorescein stain hydrophobic or hydrophilic
hydrophilic
What layer of the eye does Herpes attack
the epithelium of the cornea- replicates fast
Is the epithelium of the cornea hydrophilic or hydrophobic
hydrophobic
What kind of epithelium does the cornea have
columnar and becomes keratinized squamous cells
What part of the cornea absorbs the stain in corneal ulcers
Stroma (it is hydrophilic) and the fluorescein stain is hydrophilic
T/F: fluorescein stain stains the epithelium of the cornea
False
Fluorescein is a water-soluble dye; owing to its lipid insolubility, it does not penetrate intact corneal epithelium. Epithelial erosions or ulcers, which expose the hydrophilic stroma, allow penetration and retention of the dye.
Is Descemets membrane hydrophilic or hydrophobic?
Descemet’s membrane is hydrophobic. It’s a thick, dense, relatively transparent, and cell-free matrix that separates the corneal stroma from the endothelium.
Does not take up fluorescein stain
What is the function of the corneal endothelium
transports water from the stroma into the anterior chamber
What makes the cornea clear
1) Regularity of the collagen fibers (compared to the sclera)
2) Very low cellularity
3) Lack of blood and lymph vessels
4) Relative dehydration
-stroma is hydrophilic (sponge)
-epithelium is hydrophobic barrier
-endothelium actively pumps fluid out of cornea
Why is it challenging to deliver drugs to the cornea
relative dehydration
-stroma is hydrophilic (sponge)
-epithelium is hydrophobic barrier
-endothelium actively pumps fluid out of cornea
What 3 structures make it so the cornea is relatively dehydrated
-stroma is hydrophilic (sponge)
-epithelium is hydrophobic barrier
-endothelium actively pumps fluid out of cornea
How many corneal layers do fish have
2
Scleral cornea
Dermal cornea
a scale that covers the eye of the snake
normally shed when the skin is shed
part of cornea
spectacle
What species is corneal vascularization normal in
big horn sheep and manatees
T/F: Descemetocele stains fluorescein
False- it is hydrophobic
How does superficial corneal pathology differ from deeper corneal pathology
Superficial: see branching vascularization
Deep: see dense vessels (hedge bush appearance) tells that you are concerned with a deeper issue like uveitis
What two features of the cornea bends light into the eye
1) Angle of incidence (curvature of cornea)
2) Density of the medium (tear film) bends the light
What does LASIK surgery do
uses a laser to change the curvature of the cornea
helps for near sighted patients because it is easier to decrease the curvature than it is to increase the curvature
a fluid filled space between the cornea and lens
Anterior chamber
what maintains the shape of the globe
aqueous humor in the anterior chamber
ultra filtrate that carries nutrients for the lens and cornea
maintains shape of globe
anterior chamber
the colorful part of the eye
the iris
what regulates the amount of light that enters the eye
controlled by iris sphicter and dilator muscles
size of the pupil
a ___________ pupil allows a more precise image to be focused on the retina
smaller
what creates aqeuous humor
ciliary body
dark, pigmented structures in a horse’s eye that help reduce glare from bright light
corpora nigra
What are the different structures of the lens
1) Lens capsule (basement membrane)
2) Lens epithelium- makes cortex
3) Cortex
4) Nucleus
each layer is clear but as it gets more compact - it gets cloudy
a condition where there are multiple layers of lens packed together and the eye os cloudy
occurs in older animals
affects dim light vision
Lenticular sclerosis
what methods of accommodation do dogs and humans have
muscles in the ciliary body contract which pulls on the lens, causing the lens to stretch, which decreases the curvature of the lens
what methods of accommodation do birds have
ciliary muscles contract and push on lens, causing it to round up
What methods of accommodation do fish have
Retractor lentis moves the lens forward or backward to change focis
also have very round lens to make up for the loss of corneal refraction in aquatic environment
gel like structure between the lens and retina
made of glycoaminoglycans and some collagen, very few cells
can degenerate and become cloudy
Vitreous
how is the vitreous attached to the lens and retina
tiny ligaments, therefore vitreous can place traction on the retina and cause tears of detachments
what breeds are prone to vitreous degeneration
greyhounds and whippets
“Floaters”
when the vitreous degnerates and becomes cloudy
can lead to a retinal tear
Vitrous degeneration can lead to
retinal tear / detachments
neural tissue that is stimulated by photons
generates instaneous impulses that are modulated and sent to brain
brain then interprets this signal to determine color, contrast, brightness, movement, depth, and texture
Retina
millions of axons (of ganglion cells) extending from the retina to the brian
Retina
What are the two types of photoreceptors
1) Rods: assist with dim light vision, movement and contrast
2) Cones: color and detailed vision (Dogs have 2cones- Blue and Yellow-Green)
photoreceptors that assist with dim light vision, movement, and contrast
rods
photoreceptors that provide color and detailed vision
cones
How many types of cones do dogs have
2
1) Blue
2) Yellow-Green
this is similar to being red-green color blindness (Deuteranopia)
Deuteranopia
Red-green colorblind (canine color vision)
The reflective layer of the choroid (beneath the retina)
tapetum
What species have a cellular vs fibrous tapetum
Cellular: dogs and cats
Fibrous: horses and ruminants
is the tapetum a part of the retina or choroid
Choroid (beneath the sensory retina)
normal variation in the coloration of the eyes of dogs and cats that results in a lack of pigment in the non-tapetal fundus. This allows the choroidal vessels to be visible against the white sclera
subalbinotic
a dense network of blood vessels that covers the majority of the retina’s light-sensitive region
entire retina has blood supply
present in dog, cat, human, ruminants
Holangiotic
a small, round, yellowish spot in the center of the retina at the back of the eye that’s responsible for central vision, color vision, and fine details
present in human
macula
a type of retina where the entire retina has a blood supply
holangiotic
what species have a holangiotic retina
dog
cat
humman
ruminant
a retina where there are blood vessels over the miridian of the retina
merangiotic (rabbits)
what species have a merangiotic retina
rabbits
a retina type where the vessels are small and extend only a short distance from the disc.
present in horse, elephant, and guinea pigs
paurangiotic
What species hae paurangiotic
horses
elephants
guinea pigs
end-on vessels that feed retina can be visualized in an equine fundus exam
Stars of Winslow
Why are the Stars of Winslow relevant clinically
if a horse has a retinal detachment, blood supply is lost and the retina dies within minutes
however, dogs and cats keep their blood supply so if you can reattach the retina then everything will be ok
a term used to describe the absence of blood vessels in the retina of certain animals, such as birds and reptiles
Anangiotic
What species have an anangiotic retina
birds
reptiles
What cranial nerves are you testing with an ocular exam
II: Optic
III: Oculomotor
IV:Trochlear
V: Trigeminal
VI: Abducens
VII: Facial Nerve
VIII: Vestibulocochlear
2-8 are being tested
afferent nerve for menance and pupillar light reflex is
Optic Nerve (CN II)
what is the efferent pupillary light reflex nerve
Oculomotor (CN III)
What does oculomotor nerve innervate
Dorsal, vental, medial rectus
Ventral Oblique
Levator palpebrae superioris
What nerve innervates dorsal oblique
trochlear nerve
the only muscle that is controlled by the same side of the brain
Dorsal oblique (innervated by trochlear nerve CN IV)
afferent for palpebral reflex
trigeminal nerve (V)
what happens when the pterygoid muscle becomes inflammed
it is on the floor of the orbit, eye becomes exophthalmic
what happens when the pterygoid muscle becomes atrophied (from denervation of CN V- masticatory muscle)
enophthalmos
it is on the floor of the orbit s
What muscles does abducens nerve innervate
lateral rectus
retractor bulbi
efferent nerve for the palpebral
facial nerve
what carries parasympathetic fibers to the lacrimal gland, travel with the ophthalmic branch of CN V
facial nerve (CN VII)
Sympathetic stimulation the eye causes
1) Pupil dilation
2) Mullers muscle holds the upper eyelid up
3) Maintains some ridigity to the extra ocular muscles
What is the path of the nerve conducting sympathetic enervation to the eye
down the spinal cord from the brainstem where it exits at T1, T2, T3 in the brachial plexus then up the vagus nerve, synapsing in the cranial cervical ganglion, past the inner ear to the eye
what is ptosis
a dropping of the upper eyelid
seen with loss of sympathetic innervation to Mullers muscle (ex: Horners)
What should you use for sedation in equine eye examination
a2 agonist- detomidine, xylazine
opioid- butorphanol
What should you do for nerve blocks in equine eye examination
Auriculopalpebral- motor of upper lid (most important)
Frontal Nerve- sensation of the upper lid and cornea
fast acting, short duration (lidocaine, carbocaine)
blocks sensation to cornea and upper lid in the horse
frontal nerve block
What are different tools used in an ophthalmology exam
-Transilluminator
-Loupes
-Slit Lamp Biomicroscope
Fundoscopy
-Direct Ophthalmoscopy
-Pan-optic
-Indirect ophthalmoscopy
How can you test cranial nerve II
Pupillary light response
dazzle
menace
tracking
maze test
How can you test cranial nerve III
Movements of dorsal, ventral, medial rectus, ventral oblique, lebator palpebrae superiorsus, efferent PLR
How do you test CN V
Sensory to skin
globe cornea
mostly afferent
muscle of mastication
How do you test CN VIII
nystagmus, head tilt
How can you tell the eye is painful
Rubbing, squinting, tearing, red eyes
characterized by a difference in pupil sizes.
anisocoria
where will corneal vessels start
limbus
How should you examine the third eyelid
Retropulse the globe to evaluate
Prolapsed gland of third eyelid (cherry eye)
Scrolled cartilage (giant breeds)
Elevated in exophthalmos, Enophthalmos, Horner’s, pain
What might cause protrusion of the third eyelid
exophthalmos
enophthalmos
horner’s
pain
What should you evaluate on the irus
Texture, shape, color
-Atrophy
-Persistent Pupillary Membranes
-Neovascularization (Rubeosis irides)
-Synechia (anterior or posterior)
what is an alternative for Schirmer tear test
phenol red thread test
How do you differentiate cataracts from nuclear sclerosis
often need to dilate with tropicamide 1%
assess tapetal reflection with transilluminator
Nuclear sclerosis: hazy appearance to the center of the lens (can still see tapetal reflection)
Cataract: will completely block light
What are the different types of cataracts
1) Incipient (localized)
2) Immature (15-90%)
3) Mature (>90%)
4) Hypermature
allows fundus and lens to be evaluated
tropicamide 1%
When should you not dilate the eye with tropicamide 1%
-Increased intraocular pressure (glaucoma)
-questionable lens positon (luxation)
tapetum is part of the
choroid
where do you place the schirmer tear test strip
lateral 2/3rds of inferior eyelid
what is a normal schirmer tear test result
15mm wetting in 60 seconds
How do you perform a fluorescein stain?
do not touch dry strip to eye -moisten with saline first or mix with <1ml saline
1) Pattern of staining tells you ulcer location and depth
2) Can be used to check patency of nasolacrimal duct (Jones test)
3) Evaluate leaking aqueous (Seidels test)
Seidels test
fluorescein stain to evaluate the leaking aqueous
What are the different ways to test intraocular pressure
Schiotz: Indentation - Requires a patient patient
Tonopen: Applanation - Require Proparocaine
Tonovet: Rebound (NO proparocaine)
What happens after chronic chorioretinitis
retinal atrophy- results in hyper reflective
What is normal intraocular pressure
8-25mmHg
No more than 3-5mmHg discrepancy between eyes
not a diagnosis
technique is everything- any pressure on the neck or eyelids may alter the results
There should be no more than _______ intraocular presure discrepancy between eyes
3-5mmHg
IOP is elevated in ______ but decreased in ____________
elevated in glaucoma
decreased in uveitis and old age
evaluates the iridocorneal angle
gonioscopy
should be does for corneal ulceration
cytology +/- culture
can evaluate the globe and retrobulbar space
ultrasound
tests the electrical function of the retina
electroretinogram
What cranial nerve does touching the cornea do?
Trigeminal (afferent)
Abducens (efferent)
What cranial nerve does touching the palpebral do?
Trigeminal (afferent)
Palpebral (efferent)
Dogs with cranial nerve III damage, what way can the eye move
laterally (that is controlled by abducens VI)
Dogs with CN III damage, will the pupil be dilated or constricted
dilated (lack of parasympathetic input to the eye)
direct PLR
ipsilateral illumination
indirect PLR
contralateral illumination
