This document discusses the evaluation and differential diagnosis of acute loss of vision in pets. It begins by listing questions to ask the owner about the pet's history and symptoms. It then reviews the anatomy of the visual pathway and describes various tests used in ophthalmic examination, including menace response, visual placing, dazzle reflex, and pupillary light reflex. Potential peripheral causes involving the retina, optic nerve or disc are discussed. Specific conditions like optic neuritis, glaucoma, and retinal degeneration are also mentioned. The document concludes by contrasting peripheral vs central causes of vision loss and briefly discussing differential diagnoses involving the optic tract or visual cortex.

1. Acute Loss of Vision

2. Questions to Ask on Presentation
• When did this happen?
• What was your pet doing when it happened?
• Have you noticed your pet having difficulty
getting around lately?
• Describe why you think your pet is blind
• Does your pet have a history of seizures?
• Does your pet have a history of glaucoma?
• Is your cat on any medications?
• Have you noticed polyuria, polydipsia, lethargy,
ravenous appetite in the past 2 weeks?

3. Visual Pathway
• Photon of light  Retina (rods
and cones)  converted to an
electrical impulse  bipolar
cells  ganglion cells  Optic
Nerve (CN II)  optic nerve
enters the calvarium  optic
chiasm (crosses over) 
terminate in the lateral
geniculate nucleus (20% diverge
to generate the PLR) 
terminate in the visual cortex of
the occipital lobes of the
cerebrum

4. Ophthalmology Examination
• Observation
– Watch the animal
navigate objects in a new
environment, obstacle
course or track moving
objects
– Stand behind the animal
and throw cotton balls to
the side and see if the
animal can track them
– Ask the owner a history
of what the animal has
been doing at home

5. Ophthalmology Examination
• Menace Response
– Learned response
– CN II
– CN VII
– Cerebellum
• Ipsilateral loss of
menace

6. Ophthalmology Examination
• Visual placing response
– Hold patient to edge of table and a normal patient
should see the table and place limbs on top
• Dazzle Reflex (CN II and VII)
– Shine a bright light into the eyes, should blink
– Loss of dazzle implies a subcortical lesion
– Can be blind and have a dazzle
• Intra-ocular pressure
– Acute glaucoma causing cupping of optic nerve
• Electrophsysiological evaluation of the visual
system
– Electroretinography

7. Ophthalmology Examination
• Pupillary light Reflex
– Nerve fibers responsible for
vision and the fibers
mediating PLR have a
common pathway to the
level of the optic tract
– PLR ≠ vision, can have loss
of vision and present PLR
– Afferent arm: vision loss
and direct PLR deficit
present
– Efferent arm: no vision loss,
direct or consensual deficit
present
– Cortical: vision loss, no PLR
deficit

8. ...is it central or peripheral loss of
vision?
So you’ve determined there is a
loss of vision…

9. Peripheral Causes of Loss of Vision
• Lesion of the
– Retina
– Optic disc
– Optic nerve
– Optic chiasm
• Bilateral or unilateral
– Unilateral: pupils will be normal size (indirect response
from the good eye will continue to control the pupil of the
blind eye)
– Bilateral: pupils will be dilated
• Loss of afferent information, loss of direct or
consensual PLR

10. Differential Diagnosis: Peripheral
Optic Nerve, disc, chiasm Retina
• Optic nerve tumor
(neoplasia, granuloma,
abscess)
• Optic neuritis
• Traumatic Optic Neuropathy
• Ischemic Optic Neuropathy
• Optic nerve hypoplasia
• Glaucoma
• Coloboma
• Retinal degeneration
– Progressive retinal atrophy
– Sudden acquired retinal
degeneration
– Enrofloxacin associated
retinal degeneration in cats
• Retinal detachment
– Serous (hypertension)
– Rhegmatogenous
• Chorioretinitis
• Immune mediate retinitis

11. Differential Diagnosis: Peripheral
Optic Nerve, disc, chiasm Retina
• Optic nerve tumor
(neoplasia, granuloma,
abscess)
• Optic neuritis
• Traumatic Optic Neuropathy
• Ischemic Optic Neuropathy
• Optic nerve hypoplasia
• Glaucoma
• Coloboma
• Retinal degeneration
– Progressive retinal atrophy
– Sudden acquired retinal
degeneration
– Enrofloxacin associated
retinal degeneration in cats
• Retinal detachment
– Serous (hypertension)
– Rhegmatogenous
• Chorioretinitis
• Immune mediate retinitis

12. Optic Neuritis
• Loss of vision
• Mydriasis
• Swollen optic nerve head,
elevated disc,
peripapillary hemorrhage
• Causes: infections,
idoipathic, neoplastic,
GME, Pug encephalitis
• Treatment: CNS wok-up,
prednisolone possibly

13. Glaucoma
• Cupping of the optic
nerve
• Causes: Chronic
glaucoma, acute lens
luxation
• Tx: Emergency
glaucoma treatment!
– Mannitol
– Dorzolamide ?
• Sequelae: degeneration

14. Sudden acquired retinal degeneration,
SARD
• Acute death of
photoreceptors
• Blindness develops over
a few days to weeks
• PU, PD, PP, lethargy
Cushings
• Mydriasis with normal
appearing fundus at
first
• No treatment

15. Retinal Detachment
• Separates between
layers 9 and 10
• Serous
– Fluid, cells
– Inflammatory,
hypertension
• Rhegmatogenous
– Cataract
– Lens luxation
• Mydriasis if bilateral
• Visioin loss
• White tissue elevated
into vitreous
• Can reattach retina with
surgery

16. Central Causes of Loss of Vision
• Lesion of the optic tract, the lateral geniculate
in the thalamus, optic radiation and occipital
cortex
• Pupil size and responsiveness remains normal
• Unilateral lesion: loss is in the contralateral
visual field

17. Differential Diagnosis: Central
• Optic tract
• Lateral geniculate in the thalamus
• Optic radiation
• Occipital cortex

18. Questions?

19. References
• Ophthalmology Notes, VCS 81500, Dr. Townsend and
Dr. Stiles
• Sturges, Dr. Beverly K. Neuro-ophthalmology: The
Visible Nervous System. 2nd Annual Veterinary
Neurology Symposium, University of California, Davis.
2005.
• Grozdanic, Sinisa et. al., Antibody-mediate
Retinopathies in Canine Patients: Mechanism,
Diagnosis, and Treatment Modalities. Vet Clin Small
Anim 38 (2008) 361-387.
• Gould, D.J et.al., Canine Monocytic ehrlichiosis
presenting as acute blindness 36 months after
importation into the UK. Journal of Small Animal
Practive, Vol 41, June 2000.
• Gelatt, Kirk, et. al., Enrofloxacin-associated retinal