Sudden Blindness Flashcards
What causes blindness
1) Opacification of clear ocular media or retina / optic nerve abnormality - is it an eye problem?
2) Visual pathways abnormalities - is it a central (brain) problem
Blindness from opacification can be due to opacification in what structures
1) Cornea
2) Anterior Chamber
3) Lens
- these changes are often not sudden *
sudden blindness is often the back part of the eye
What disease can cause cornea opacification due to pigmenetation, neovascularization, edema and scarring of the cornea
Chronic superficial keratitis (pannus)
Why might a patient be blind due to cornea opacification
1) Advanced corneal endothelial dystrophy with edema
2) Chronic superficial keratitis (pannus)
How might the anterior chamber be opacified
hyphema from trauma to the eye
this acute change might cause blindness
What change to the lens can lead to blindness
Cataracts (could be from diabetes)
For a blind dog, what should you do when youve ruled out opacification of the cornea, anterior chamber, and lens
look at the back of the eye for answers (ie optic nerve and retina) and brain
Where does PLR get processed
Midbrain
What is the path of the visual pathway
1) Retina
2) Optic nerve
3) Optic chiasm
4) Optic tract
5) Lateral geniculate nucleus
6) Optic radiation
7) Visual cortex
Bilateral sudden blindness is usually noticed by
owner (behavior changes)
Bilateral opthalmic disease often means
Systemic disease
workup for systemic disease
-history
-complete physical exam
-complete ophthalmic exam
-minimum data base (CBC, chem, UA, and culture) +/- titers for infectious diseases
What medications may cause retinal toxicity
Enrofloaxcin
Ivermectin
can be acute
What tests can you do in your neuro-ophthalmic exam?
1) Menace response
2) Maze testing
3) Dazzle reflex
4) Direct / Indirect PLR
What nerves does the pupillary light reflex test
CN II- Optic (afferent)
CN III - Oculomotor (efferent)
What is the direct response to PLR
Stimulation (light) and response (pupil constriction) in the same eye
What is the indirect (consensual) response to PLR
Stimulation (light) and response (pupil constriction) in the contralateral eye
T/F: PLR assesses vision
False - the reflex arch goes through the midbrain
Not the visual cortex in the occipital lobe
T/F: the PLR reaches the visual cortex in the occipital lobe
False - it goes through the midbrain, not the occipital lobe
it is a reflex arch
What will the result of PLR be if there are afferent lesions (ie retina, optic nerve, optic chiasm, optic tract)
The patient will have an absent or sluggish PLR
What will the result of the PLR be if there are efferent lesions (sympathetic, CN III, mechical at iris)
The patient will have an absent or sluggish PLR
With afferent arm lesions the vision is _________ and PLR are _________
Vision is abnormal
PLR is abnormal
With cortical lesions, vision is _______ and PLR are ______
vision is abnormal
PLR are normal
With efferent arm lesions, vision is ________ and PLR are ________
Vision is normal
PLR are abnormal
What is the dazzle reflex
a really bright light is shined in one eye at a time
Squint repsonse
tests Optic (CN II) and Facial (CN VII)
subcortical reflex - does not require processing in the visual cortex
What two nerves does the Dazzle reflex test
CN II (afferent) and CN VII (efferent)
T/F: a positive dazzle reflex means vision is presnet
False - it is a subcortical reflex: does not require processing in the visual cortex
a postive dazzle does NOT mean vision is present
What do you need to do the dazzle reflex
a very bright focal light source
What nerves does the menace response test
Afferent: CN II
Efferent: CN VII
The menace response requires what to be intact
a functioning visual cortex (to process information from CN II) and brainstem to coordinate the blink response
this is not a reflex, it is a learned response
T/F: menace is a reflex
False - it is a learned response
a functioning visual cortex (to process information from CN II) and brainstem to coordinate the blink response
What is the maze test
add animal to a novel environment
change pattern with each run
assess in bright (photoptic) and dim (scotopic) lighting (evaluates different parts of retina)
Avoid auditory cues
dont let the patient get hurt
What tests can you do to assess vision
-Maze testing
-Visual placing
-Cotton ball
-Visual cliff
-Laser pointer
What is visual placing test for assessing vision
bring animal close to edge of table, they will extend forelims
alternate covered eyes
Cotton balls for assessing vision need to be
Silent
Odorless
What is the visual cliff for assessing vision
Use clear plastic extending over the edge of the table
Patients with cortical lesions have loss of ______ but retain __________
patient with cortical lesions have a loss of menace but retention of dazzle and PLR’s will be normal (dazzle and PLR are processed in the midbrain)
Patients with retina and optic nerve leasion have loss of what
Loss of:
1) Menace response
2) Dazzle reflex
3) PLR
T/F: cortical lesions have loss of menace
True
T/F: cortical lesions have loss of PLR
False
T/F: cortical lesions have loss of dazzle
False
Lesions to what part of the optic tract have losses in menace response, dazzle reflex, and PLR
Retina and optic nerve lesions
You have a patient with blindness, dilated pupil, and sluggish PLR. where might you localize the lesion
Retina or optic nerve
Retinal diseases causing blindness often involve
involve diffuse bilateral ocular inflammation
often secondary to systemic disease or immune mediated
What might cause chorioretinitis
1) Trauma
2) Infectious diseases
3) Immune mediated diseases (Uveodermatologic syndrome, idiopathic)
4) Neoplasia
5) Blood/vascular disorders resulting in disruption of the blood eye barrier
-Hypertension (cats)
-Hyperglobulinemias - MM, lymphosarcoma, Ehrlichia canis
What might disrupt the blood-eye barrier and lead to chorioretinitis
1) Hypertension cats)
2) Hyperglobulinemias
-MM
-Lymphosarcoma
-Ehrlichia canis
Any inflammatory chorioretinal disease can result in fluid/cell accumulation beneath the retina leading to
Retinal detachment
-Separation of retina from RPE
Retinal detachment causes what change on fundus exam **
decreased tapetal reflectivity and a generalized hazy appearance
-fluid and cells go under the retina (giving hazy area)
-can have focal areas of retinal detachment
In complete retinal detachment, the retina remains attached at the
optic nerve head
What is a great diagnostic method for retinal detachment
eye ultrasound - will have a classic “seagull sign” of retinal detachment
What ultrasound sign gives you retinal detachment
a classic “seagull sign” of retinal detachment
Optic neuritis is typically concurrent with ______ ***
Retinal disease (present just like blindness due to diffuse retinal disease)
sometimes the retina is normal
Optic neuritis is unilateral or bilateral **
Often bilateral *
What will the PLR be with optic neuritis *
Abnormal PLR = mydriasis
How do you diagnose optic neuritis *
fundic exam
-optic nerve swelling or hemorrhage
-peripapillary edema (optic nerve head may appear normal if acute or mild disease)
CSF analysis
MRI or CT
With optic neuritis, the optic nerve head may appear normal if acute or mild disease (not having the classic swelling, hemorrhage, and peripapillary edema)
What can help you with your diagnosis **
MRI or CT will help
What does optic neuritis look like on fundic exam
-optic nerve swelling or hemorrhage
-peripapillary edema (optic nerve head may appear normal if acute or mild disease)
What will optic neuritis look like on MRI
-fuzzy (staining darker)
-vessels
-thicker, inflammed
What are the infectious causes optic neuritis
1)toxoplasmosis (protozoal)
2) Cryptococcosis
3) Borreliosis (rickettsial)
What are the causes of optic neuritis
1) Infectious: Toxoplasmosis, Cryptococcosis, Borreliosis
2) Immune mediated: GME
3) Idiopathic (50% of dogs)
4) Trauma
5) Neoplasia
Most cases of optic neuritis (~50%) are idiopathic. How do you treat this _____ *
Must rule out infectious cause first
if treated early and responsive to immunosuppressives, the prognosis is fair for long term vision
ie treat with Azathioprine, Prednisone, Mycophenolate
What are the non-infectious causes of blindness
No systemic involvement
-SARDS
Systemic involvement
-Hypertensive Retinopathy (Cat > Dog)
-Uveodermatologic Syndrome (Dog)
What are your differentials for blind OU, normal fundus, abnormal PLR (mydriasis)
1) Sudden Acquired Retinal Degeneration Syndrome (SARDS)
2) Optic chiasm and/or optic tract disease. Do ERG for diagnosis to help localize abnormality
Patients with Sudden Acquired Retinal Degeneration Syndrome (SARDS) are blind with ______ fundus and ______ PLR
Blind with normal fundus and abnormal PLR (mydriasis)
What is the onset of blindness of Sudden Acquired Retinal Degeneration Syndrome (SARDS)
over a day to weeks
What does SARDS stand for
Sudden Acquired Retinal Degeneration Syndrome (SARDS)
What causes Sudden Acquired Retinal Degeneration Syndrome (SARDS)
cause unknown
-immune mediated attack on the retina
-bilateral
How do you differentiate Sudden Acquired Retinal Degeneration Syndrome (SARDS) from optic chiasm and/or optic tract disease *
Do an ERG to help localize the abnormality
SARDS will have abnormal ERG
Sudden Acquired Retinal Degeneration Syndrome (SARDS) has a systemic clinical presentation similar to **
Hyperadrenocorticism (PU/PD, polyphagic)
Increases in ALT, ALP, cholesterol
With Sudden Acquired Retinal Degeneration Syndrome (SARDS), what does the fundus look like on ophthalmic exam
Normal early in the disease course but will show diffuse degeneration months after the onset of blindness
Does Sudden Acquired Retinal Degeneration Syndrome (SARDS) affect the rods or cones first
Rods
What is the typical signalment of Sudden Acquired Retinal Degeneration Syndrome (SARDS)
Middle aged dogs (females more common)
How do you diagnose Sudden Acquired Retinal Degeneration Syndrome (SARDS)
ERG confirms the diagnosis (no retinal function = flat line)
specific tests for Cushings generally negative
How do you treat Sudden Acquired Retinal Degeneration Syndrome (SARDS)
No scientifically proven treatment
permanent blidness
What test measures retinal function
Electroretinogram (ERG)
looks at photoreceptors
What will the ERG show in patients with optic neuritis *
Normal ERG as the abnormality is in the optic nerve (not the retina) this patient will have an a, b, and c wave present
Increase in blood pressure, specifically greater than _____________ systolic in the cat causes vasoconstriction
> 160mmHg systolic in cat
How does systemic hypertension affect the eye **
Prolonged vasoconstriction (of systolic BP >160mmHg in cat) causes necrosis of blood vessel walls
Necrosis of retinal vessels leads to retinal hemorrhages, exudation, and edema
Similar changes in choroid leading to subretinal edema and exudation
What are the 3 features of hypertensive retinopathy **
1) Retinal hemorrhage
2) Retinal or subretinal fluid -> edema or exudation
3) Complete retinal detachment
What kind of cats typically get hypertensive retinopathy
1) Old cats
2) Most often see ocular signs with renal disease * (may also see with cardiac disease and hyperthyroidism
What kind of cats typically present with hypertensive retinopathy
Old cats presenting with bilateral mydriasis and blindness
T/F: cats can regain vision after hypertensive retinopathy
True up to 50% will regain some vision if treated
Treat the systemic hypertension AND underlying systemic disease
-Amlodipine, benazepril
How might you treat systemic hypertension causing hypertensive retinopathy
-Amlodipine, benazepril
What cause Uveodermatologic Syndrome (VKH syndrome)
immune mediate disease on the dermal and uveal melanocytes
skin and eye disease = loss of pigment +inflammation
What kind of dogs get Uveodermatologic Syndrome (VKH syndrome)
Young adult dogs
Akita *, Samoyed, Siberian Husky (arctic breeds) predisposed
Do the ocular or derm issues tpyically present first with Uveodermatologic Syndrome (VKH syndrome)
Ocular signs usually first
signs:
1) Anterior uveitis (esp in dogs with brown eyes)
2) Sudden blindness (chorioretinitis / retinal detachment)
What are the 3 ocular changes are seen with Uveodermatologic syndrome *
1) Anterior uveitis (esp in dogs with brown eyes)
2) Sudden blindness (chorioretinitis / retinal detachment)
What are the dermatologic signs seen with Uveodermatologic syndrome
eyelid, nose and skin depigmentation
these signs are typically the second signs seen
How do you diagnose Uveodermatologic Syndrome
-Routine lab tests normal
-Immune function tests non-diagnostic
-Histopathology of skin shows
Interface dermatitis
Lichenoid pattenr
a condition that causes localized patches of white hair due to the absence or reduction of melanin pigment in the hair follicles.
poliosis
a dermatologic sign of uveodermatoligc syndrome
autoimmune disorder that causes white patches to appear on the skin
vitiligo
a dermatologic sign of uveodermatologic syndrome
How do you treat uveodermatologic syndrome
1) Treat uveitis
-1% prednosolone acetate and 1% atropine sulfate (topical)
-Subconjunctival steroids (vision may return if treated acutely)
2) Systemic immune suppression (Azathioprine, Prednisone)
8yo female mini poodle appears blind acutely. Normal fundus. What is your differential diagnosis
SARDS
do an ERG for diagnosis
