Ocular Fundus Flashcards
What is the vascular layer of the fundus
choroid
What are the 3 ways you can do fundus examination
Direct
PanOptic
Indirect
what are the disadvantages of direct ophthalmoscopy
1) Very in the face- biting dogs and cats
2) Very magnified - hard for small animals. difficult to do thorough exam- up to 15X
What is an advantage of PanOptic
1) Longer working distance
2) Wider field of view
3) Gives a right side up image
What is an advantage of direct ophthalmoscopy
the head has different lights
white for exam, blue for stain
slit beam for aqeuous flair
What is indirect ophthalmoscopy
Indirect lens and transilluminator
disadvantages: upside down and backwards
When you say youre doing a fundic exam. What structures are visualized?
1) Fundus (tapetal and non)
2) Optic head head
3) Retinal vessels
where is the optic disc location in horses
non-tapetal fundus
where is the optic disc location in cats
tapetal fundus
where is the optic disc location in dogs
At the tapetal /nontapetal junction
areas where theres holes in the sclera for axons to pass through
lamina cribosa
the tapetum is an extension of the
choroid
What are the 6 layers of the fundus **
1) Sclera with lamina cribosa
2) Choroidal vessels with pigment
3) Optic nerve head
4) Tapetum
5) Retina - Retinal pigmented epithelium (RPE) and nonpigmented RPE
6) Retinal vessels
central area of the retina where there is no pigment and allows the tapetum to show through
non-pigmented retinal epithelium
a transparent tissue that you dont really see on fundic exam unless it is detached or thickened with cells or fluid
Retina
What are the 10 layers of the retina
inner limitng membrane
nerve fiber layer
ganglion cells
amacrine cells
bipolar cells
horizontal cells
muller cells
outer limiting membrane
rod and cones
pigmented epithelium
What part of the brain is important in the visual pathway- PLR
the midbrain
What kinds of color vision for dogs have
dichromatic color vision
why might you see tapetal hyperreflectivity ***
due to loss of retina from atrophy or degeneration or detachment
What does a detached retina look like on fundic exam *
a thin veil of retina folded over the optic nerve head
Why might the tapetum look hyperreflective on fundic exam *
When the retina is detached, you no longer have the retina over the tapetum so the tapetum looks really bright
the retina dampens the tapetal reflectivity
What dampens the tapetal reflectivity
the retina
What are the 4 different types of retinal vessel patterns
1) Holangiotic
2) Paurangiotic
3) Merangiotic
4) Anangiotic
What kind of retinal vessel pattern does a dog have
Holangiotic
-3 to 4 major vennules
-variable small arterioles
What kind of retinal vessel pattern does a horse have
Paurangiotic - small retinal vessels extending only a small distance from optic nerve head
What kind of retinal vessel pattern does a guinea pig have
Paurangiotic - small retinal vessels extending only a small distance from optic nerve head
What kind of retinal vessel pattern does a rabbit have
Merangiotic
-no tapetum
-optic nerve head is myelinated and horizontal streak
-vessels only in focal region
What kind of retinal vessel pattern does a cat have
Holangiotic
-3 to 4 major vennules
-variable small arterioles
What kind of retinal vessel pattern does a ruminant have
Holangiotic
-3 to 4 major vennules
-variable small arterioles
What kind of retinal vessel pattern does a camelid have
Holangiotic
-3 to 4 major vennules
-variable small arterioles
What kind of retinal vessel pattern does a human have
Holangiotic
-3 to 4 major vennules
-variable small arterioles
What species have a paurangiotic vascular pattern
Horses and Guinea pigs
Retinal vessel pattern where there a 3-4 major venules
variable small arterioles
present in : dogs, cats, ruminants, camelids, humans
Holangiotic
What species have a holangiotic vascular pattern
Dogs
Cats
Ruminants
Camelids
Humans
What species have a merangiotic vascular pattern
Rabbits
-no tapetum
optic nerve head is myelinated and horizontal streak
vessels only in focal region
Rabbits
-no tapetum
optic nerve head is myelinated and horizontal streak
vessels only in focal region
merangiotic vascular pattern
vascular pattern where there are small retinal vessels extending only a small distance from optic nerve head
Paurangiotic
present in horses and guinea pigs
retinal blood vessel pattern where there are no retinal vessels
often have pectin which is vascular
present in birds, beaver, chinchilla, porcupine, armadillo, bat
Anangiotic
In species with angiotic vascular pattern what is vascular
Pecten is the blood supply
What species lack retinal vessels
Angiotic species - birds, beaver, chinchilla, porcupine, armadillo, bat
What is the optic nerve head made of
Axons of the ganglion cells
What species have myelinated optic nerve heads
dogs
ruminants
What species have nonmyelinated optic nerve heads
cats
horses
camelids
T/F: different dogs have different degrees of optic nerve head myelination
True
In what species would you see an optic nerve head that is darker, more grey and more consistent shape
those that are nonmyelinated - cats, horses, camelids
In dogs and ruminants, what causes the optic nerve head to be lighter in color and different sizes and shapes
the myelination (degree of myelination varies)
Why do you need to know whether the optic nerve head is myelinated or unmyelinated?
Myelin changes the size, shape and color of the nerve head
you dont want to mistake normal myelination for pathology
What are the 3 parts of the dog optic nerve head
1) Venous anastomosis “ring”
2) Neurorim
3) Physiologic cup (where they lack axons)
what are the features of the canine retina **
1) Retinal veins (generally 3-4 main veins)
2) Cilioretinal artery- much smaller than the veins
3) Optic nerve head with venous anastomosis and physiologic cup
4) Tapetal and Nontapetal retina
If the retina is transparent, what is beneath?
1) RPE (retinal pigment epithelium)
-anchors retina to choroid
-pigmented in the non-tapetum
2) Choroid
3) Sclera
-anchors retina to choroid
-pigmented in the non-tapetum
retinal pigment epithelium
the tapetum is the inner most layer of the
choroid
What you see beneath the retina depends on
1) Whether you are looking at the tapetum - blocks visualization of underlying tissues
2) Whether you are looking at non-tapetum (how much pigment is present)
When doing a fundic exam, why do we not see the choroidal pigment or blood vessels
because the tapetum obscures the underlying choroidal vessels and pigment
inner layer of the choroid
upper 1/2 of ocular fundus
variable size in dogs
reflects photons of light not captures by photoreeptors (rods and cones)
Tapetum
why might you see the choroidal vessels on fundic exam
absent tapetum
1) Blue eyes dogs
2) Blue eyed cats with light fur
What dictates the tapetal-nontapetal junction border *
the border will vary from sharp to ragged in relation to the hair coat length
short haired = sharp border
long haired = ragged border
What can cause tapetum pattern variations
lack of tapetum
lack of pigment in retinal pigmented epithelium (RPE) or choroid
upon fundus exam, if a dog lacks a tapetum, what is the darker region
likely pigmented RPE
What influences the nontapetum appearance
1) Retinal pigment epithelium (RPE)
2) Choroid
related to the amount of pigment in these structures
T/F: there is variable amount of pigment in the RPE and choroid
true
-related to the amount of pigment in the haircoat of color of iris
generally darker haircoat and iris = more heavily pigmented nontapetum
In non-tapetal area. generally, the darker the haircoat and iris the more
heavily pigmented nontapetum
In non-tapetal area, what obscures the choroidal vessels and sclear
heavy pigment in the RPE
when not pigmented, choroid vessels and sclera are seen
What does it mean when a dog has a red reflex
red reflection from the eye of a dog with no or little pigmentation in the choroid
What structure in the eye tells you it is a ruminant (goat)
corpora nigra
camelids have ribbons shaped corpora
What are common ocular developmental abnormalities (congenital)
1) Collie eye anomaly
2) Retinal dysplasia, oculoskeletal dysplasia
What are common non-inflammatory ocular degeneration conditions
1) Progressive Retinal Atrophy (inherited)
2) Drug toxicitiy
3) Nutritional deficiencies
Are developmental / congenital abnormalties of the fundus more common in the dog or cat
Dog
What causes collie eye anomaly (choroidal hypoplasia)
Autosomal recessive inheritance - causes abnormal development of the choroid
dont want to breed two carries
What congenital disease of the fundus do collies commonly get
Choroidal Hypoplasia (Collie Eye anomaly)
Is Choroidal Hypoplasia (Collie Eye anomaly) typically unilateral or bilateral
Always bilateral but not always detectable clinically in both eyes
How is Choroidal Hypoplasia (Collie Eye anomaly) graded
On a grading system I-V
based on severity of ocular abnormaltities
What are the Grades of Choroidal Hypoplasia (Collie Eye anomaly)
I: vascular tortuosity
II: Choroidal hypoplasia: loss of normal tapetum
III: optic nerve coloboma: can lead to blindness
IV: retinal detachement : blind eye
V: ocular hemorrhage : blind eye
With Choroidal Hypoplasia (Collie Eye anomaly), what grades a blind at birth
IV: retinal detachement
V: ocular hemorrhage
III: can lead to blindness (optic nerve coloboma)
What do you see with choroidal hypoplasia
lack of vessels, pigment, and tapetum
this places the dog at grad II choroidal hypoplasia
How do you test for Choroidal Hypoplasia (Collie Eye anomaly)
Optigen - genetic testing for retinal diseases (blood test)
use these to prevent grade 4 and 5 and detect CEA carriers
goal is to avoid breeding two carriers
What breeds are known to carry Choroidal Hypoplasia (Collie Eye anomaly)
Collie
Border Collie
Sheltie
Australian shepherd
Lancashire heeler
nova scotia duck tolling retreivers
silken windhound
longhair whippet
bearded collie
boyken spaniel
english shepherd
hokkaido dog
mini american shepherd
prevalence in 60% in US collies
low prevalence in border collies and australian shepherd
Goal is try to avoid breeding two carriers
Retinal Dysplasia is common in what breds
Labradors, English Springer Spaniel, Golden Retrievers, Rottweiler, Yorkie, American Cocker, Beagle
What might cause Retinal dysplasia
1) Abnormal retinal differentiation in utero (abnormal formation of retinal layers)
a) Genetic / Inherited in dogs
b) In utero or early neonatal viral infection (cats)
+/- other ocular abnormaltities like microophthalmos, coloboma
How do dogs vs cats typically get retinal dysplasia
Dogs: genetic / inherited
Cats: In utero or early neonatal viral infection
What other ocular abnormalties occur with retinal dysplasia
Microopthalmos
Coloboma
What are the normal forms of retinal dysplasia
1) Retinal Folds: dogs will have normal vision
2) Geographic: abnormal vision
3) Complete dysplasia and detachment: abnormal vision
labs typically get lower levels, springer spanies and samoyeds typically get more severe
What will you see on your fundic exam in a dog with retinal dysplasia
Retinal folds: small linear lines in the fundus that can be different sizes
can be geographic (wide spread)
can also see areas of retinal detachement
What breeds commonly get retinal dysplasia AND other non-ocular abnormaltieis
Samoyed
Labrador
Australian Shepherd
Doberman
Chow
What breeds commonly get oculoskeletal dysplasia
Labrador and Samoyed
Oculoskeletal dysplasia is associated with
multiple skeletal and ocular defects when homozygous for gene
In oculoskeletal dysplasia.
Homozygous animals have ______________
Heterozygous animals have
______________
Homozygous: skeletal and ocular defects
Heterozygous: Retinal folds only (no skeletal defects)
How do you test for oculoskeletal dysplasia
Genetic testing - RD/OSD (drd) variable inheritace patterns
If a patient is homozygous for oculoskeletal dysplasia, what signs are seen
1) Dwarfism = abnormal bone growth (radius, ulna, tibia)
-Delayed epiphyseal development
-UAP, separated coronoid process
-Hip dysplasia
-Domed forehead (Samoyed)
2) Ocular abnormalties
-Retinal dysplasia or detachement
-Cataract
-Superficial corneal opacities
-Tapetal hypoplasia
-Prominent hyaloid artery remnant
-Liquefied vitreous
It is important to do genetic blood tests on labrador or samoyed with _______ prior to breeding
retinal folds
What skeletal abnormalties are seen when Homozygous for oculoskeletal dysplasia
1) Dwarfism = abnormal bone growth (radius, ulna, tibia)
2) Delayed epiphyseal development
3) UAP, separated coronoid process
4) Hip dysplasia
5) Domed forehead (Samoyed)
inherited progressive rod-cone degeneration
Progressive retinal atrophy (PRA)
How does Progressive retinal atrophy (PRA) typically progress
Night blindness (loss of rods) then progresses to day blindness
vision loss typically starts at middle age
What causes Progressive retinal atrophy (PRA)
autosomal recessive
also autosomal dominant and X-linked
>40 breeds have been identified with a form of PRA
this leads to progressive rod-cone degeneration
What are the clinical signs of Progressive retinal atrophy (PRA)
-Progressive loss of night vision
-Increased tapetal reflectivity
-Retinal vascular attenuation
-Optic nerve atrophy
-Day vision loss
How might you diagnose PRA
-Genetic testing
-Fundus examination
-Electroretinogram * showing minimal retinal function
What will you see on fundic exam of early Progressive retinal atrophy (PRA)
1) Vascular attenuation
2) Mild tapetal hyperreflectivity
3) Mild optic nerve atrophy - appears more scalloped
night vision deficits
What might you see on fundic exam of advanced Progressive retinal atrophy (PRA)
1) Marked vascular attenuation
2) Marked tapetal hyperreflectivity
3) Moderate optic nerve atrophy
day and night vision deficits
What might you see at end-stage progressive retinal atrophy
1) Vasculature almost completely gone
2) Extreme tapetal hyperreflectivity
3) Severe optic nerve atrophy
blind eye
What breeds of cats commonly get Progressive retinal atrophy (PRA)
Abyssinian and Persian cats
How is Progressive retinal atrophy (PRA) different in cats
1) Abyssinian and Persian Cats
2) Progresses much earlier onset (progresses over the next 1-2 years to result in blindness)
Deficiency of what nutrient results in retinal degeneration in cats
Taurine - can also develop cardiomyopathy
How do you stop the progression of nutritional retinal degeneration in cats
Dietary supplementation of taurine - up to 500mg PO BID
How does Taurine deficiency retinopathy typically progress in cats
1) Retinal signs 3-7 months after starting deficient diet. Initial loss of cones leading to total blindness if diet not corrected
-more of a day blindness
2) Bilaterally symmetric
3) Football shaped lesions in the central retina (hyperreflective) can progress to larger lines
Why should you not use Enrofloxacin in cats
acute, severe, retinal degeneration and blindness
Enrofloxacin is only indicated in cats when
there are no alternatives to fluoroquinolones
make sure to keep dose as low as possible
do not exceed 2.5mg/kg bid
Enrofloxacin dose in cats should not exceed
do not exceed 2.5mg/kg bid
What might you see on fundic exam in a cat with enrofloxacin toxicity
-Acute, severe, retinal degeneration and blindness
-Tapetal hyper-reflectivity, vascular attenuation
-Vision loss may be reversible when the drug is stoppe
What is a safer fluoroqinolone in cats, that isnt enrofloxacin
Pradofloxacin - still has its risks though
What might start ocular inflammation
Tissue damage
-Infection
-Immune mediated
-Trauma
-Neoplasia
inflammation of the eye causes
leakage of cells and fluid from the blood vessels
-Retinal blood vessels
-Choroidal blood vessels
ie chorioretinitis
this can manifest as detachment or hemorrhage, cant tell cause of inflammation
What will you see with chorioretinitis on fundic exam ***
Cells and/or fluid beneath or within the retina
1) Decreases tatepal reflectivity (hopreflective/ active lesion)
2) Retinal elevation or detachement from chorioretinitis
What occurs as a result of inflammation to the retina
degeneration occurs in area of previous inflammation
focal or diffuse, depending on where the inflammation was
Lost of retinal function ensues
once detached, the retina degenerates very quickly in dogs (cats less so)
No matter the cause, retinal degeneratio nresults in a thinner layer of tissue covering the tapetum causing ________ *
increased tapetal reflectivity in the area of the retinal thinning
if the retina is not there then you are seeing straight back to the tapetum
How might you workup the cause of inflammatory retinal disease
-History
-Good PE
-Minimum data base
-Titers
-Aqueous or Vitreous centesis
What might cause chorioretinitis
1) Inflammation- trauma, infection, immune mediated, neoplasia
2) Vascular disease - systemic hypertension may also alter vascular permeability of choroidal and retinal vessels
the appearance of the inflammation may not help narrow the diagnosis
What might systemic disease might cause chorioretinitis in the cat (bilateral)
FIP
Cryptococcosis
Systemic Hypertension
less common: toxoplasmosis, FeLV, FIV, FHV-1, Bartonella
What might systemic disease might cause chorioretinitis in the dog (bilateral)
Distemper
Rickettsial disease
Systemic mycosis
Uveodermatological syndrome
What is your top differential for a young cat with anterior and posterior uveitis bilaterally
and generalized chorioretinitis with vasculitis
FIP
What ocular changes might you see in a cat with FIP
Anterior and/or posterior uveitis
Generalized chorioretinitis with vascultitis
Fibrin clot in anterior chamber
Dull and fuzzy appearance which is caused by fluid and cells within and beneath the retina blocking the tapetal reflection
Is anterior or posterior uveitis more common in cryptococcosis in cats
Posterior uveitis
What ocular changes can cryptococcosis cause in cats
-Anterior and posterior uveitis (most common posterior)
-Optic neuritis
-Multifocal areas of tapetal hyporeflectvitvity
Toxoplasmos typically causes anterior or posterior uveitis
anterior uveitis
What agent in the cat is usually accompanied by systemic illness if chorioretinitis is present
Toxoplasmosis
CNS signs!!!
How does FeLV typically cause uveitis
by causing lymphoma/sarcoma
lymphosarcoma can affect the optic nerve and retina-choroid
these raised neoplastic lesions can be shown on fundic exam
What are the ocular findings of dogs with Canine distemper virus
1) Conjunctivitis
2) KCS
3) Chorioretinitis
4) Optic neuritis
sick puppies
What ocular signs do you see with rickettsial disease like ehrlichia and rocky mountain spotted fever
1) Anterior and posterior uveitis/ choroiditis
2) Ocular hemorrhage
3) Retinal detachment
What does Prototheca (algae) cause
granulomatous chorioretinitis
What are the ocular changes seen with systemic mycosis from blasto, crypto, husto, coccidiodomycosis, prototheca
1) Multifocal areas of chorioretinitis causing tapetal hyporeflectivity
2) Subretinal exudation
Is immune mediated chorioretintis unilateral or bilteral
Both!
How do you treat immune mediated chorioretintis
systemic cyclosporine
-topicals wont penetrate the vitreous
