Clinical Approach to Vision Loss

Question 1

What is the order of the structures involved in the visual tract?

Answer 1

Eye
Optic Never
Optic Chiasm
Optic Tract (Diencephalon)
Lateral Geniculate Nucleus (mid brain)
Optic Radiation
Ocular Cortex (Cerebellum)

Question 2

If you have a lesion at the level of the optic nerve in the left eye, what can you expect the result to be?
OS: Menace?
OS: Pupil size and PLR?
OD: Menace?
OD: Pupil Size and PLR?

Answer 2

OS: Menace Absent
OS: Pupil slightly larger and no PLR
OD: Menace Present
OD: Normal pupil and PLR present (direct and consentual)

Question 3

Where do visual signals cross in the brain?

Answer 3

Optic chiasm

Question 4

If you have a lesion at the level of the cerebellum on the right side in addition to the one at the optic nerve, what can you expect the result to be?
OS: Menace?
OS: Pupil size and PLR?
OD: Menace?
OD: Pupil Size and PLR?

Answer 4

OS Menace - absent
OS: Pupil slightly larger and PLR normal
OD: Menace present
OD: Pupil and PLR normal

Question 5

What is the pathway for pupilary control?

Answer 5

Eye
Optic nerve
optic chiasum
optic tract
optic radiation
ocular cortex
pretectlal nuclei
oculomotor nucleus
oculomotor nerve
ciliary ganglion

Or
T1 - T3
Vasosympathetic trunk
cranial cervical ganglion
middle ear
(dilation)

Question 6

Which muscles of the eye innervate the iris muscles?

Answer 6

Sphincter muscle
-parasympathetic
-CN III

Dilator Muscle
-Sympathetic
-T1-T3

Question 7

What is anisocoria?

Answer 7

Unequal pupil size
-Can see fine

Question 8

If there is a lesion in the oculomotor nerve, then how does that effect the eye?

Answer 8

Parasympathetic to the pupil
-dysfunction of the iris muscle, cat cant bring down so widely dilated

Question 9

I there is a lesion aft the middle ear, how does that effect the pupil size?

Answer 9

Sympathetic
-constriction of the pupil, Horner’s syndrome
Drop in upper eyelid

Question 10

What are some things you should consider when you see anisocoria?

Answer 10

How dramatic is the difference in pupil size?
-Mild then afferent
-Dramatic then efferent

Which pupil is the abnormal one?
-Consider light versus dark
-Animal stress

Consider non-neurologic causes
-Mydriasis - iris atrophy, glaucoma, pharmacologic
-Misosis - uveitis, keratitis, posterior synechia, pharmacologic

Question 11

What is the most common, non-neurologic cause of mydriasis in one eye?

Answer 11

Iris Atrophy - agining relatd in older small breed dogs

Question 12

What will you see on a normal optho exam if there is an injury in the eye itself and you have +/- PLR’s?

Answer 12

+/-PLR deficit
-Opacification of ocular media (cataracts) - still have PLR/Hyperemia
-Retinal Disease (PRA, Chorioretinitis, detachment)- effect PLR

Question 13

What will you see on an abnormal optho exam if there is an injury in the eye itself and you have diminished/absent PLRs?
(Dazzle reflex may be dimished as well)

Answer 13

Retinal detachment (depend on severity and chronicity

Optic neuritis, optic nerve hypoplasia

Question 14

What is the dazzle reflex?

Answer 14

When the eyelids involuntarily blink in response to sudden bright light or glare (substitute for PLR)

Question 15

What will you see on an normal optho exam if there is an injury in the optic tract or optic chiasm that results in normal optho exam but diminished, incomplete or absent PLR?

Answer 15

SARDS (sudden acquired retinal degeneration syndrome) - PLR often present but slightly diminished
Retrobulbar optic neuritis, optic nerve/chiasm neoplasia optic tract lesion

Question 16

What will you see on annormal optho exam if there is an injury in the optic tract or optic chiasm that results in normal optho exam but normal PLR?

Answer 16

Thalamocortical lesions
Cortical blindness

Question 17

Case:
Acute vision loss 1 week ago - onset 24-48hrs, weight gain, PU, PD over past 2 months.
PE: Anxious, panting, increase heart rate
Opthalmic exam:
-Negative menace but positive but reduced dazzle both sides
-PLR positive but reduced, direct and consensual
-STT - normal
-IOP - normal
-Adnexa, cornea, anterior chanber normal
-Iris slightly dilated in room lighting
-Lense - normal limit
Posterior - increased vessel size hyperreflexive tapetal reflex
Diagnosis?

Answer 17

Blindness due to bilateral retinal retrobulbar optic nerve, optic chisam, bilateral optic tract or visual cortical lesion
Rule out - cushings, bloodwork diabetes, electroretingoram

Flat electroretnogram = not functioning right

Canine sudden acquired retinal degeneration syndrome
-No treatment - blind for life

Question 18

What is Canine Sudden Acquired Retinal Degeneration Syndrome and who gets it?

Answer 18

Diagnostic Triad: signs, electroretinogram flat
Idiopathic
-Signalment: middle age to older dogs, spayed female, overweight, breed over-represented
-May have other sytndromes PU/PD, polyphagia, weight gain, panting, anxiety , increase SAP, and ALT, Cholesterol and isothernuria

-Resolve over several months

Question 19

Case:
Toy Poodle 8yr
-Vision loss 3 weeks ago - running into things
-clumsy in the dark
-Increased HR

Ophthalmic exam:
negative menace, severly diminseh dazzle both sides
-no PLR orconsentual either side
-STT, IOP,Conrea normal
-Adnexa - staining of tears
-Iris - dilated in room lighting
posterior - bright, small vessels

Diagnostics and diagnosis?

Answer 19

Problems: Blindness due to bilateral retinal disease, epihora

Retinogram

Diagnosis: Retinal atrophy
-no treat
negative for vision and life ok

Question 20

What is progressive retinal atrophy?

Answer 20

-Hereditary disorder
-Heterogenous group of diseases - rod and cone degenerative disorders
-Rate progress variable (fast in young)
Secondary cataract formation common

See fundus changes - vascular attenuation, tapetal hyperreflectivity, optic atrophy

Question 21

What is optic neuritis?

Answer 21

Causes: Infectious disease, neoplasia, fungal, inflammatory, MUE

Signs: negative menace and PLR, decrease teat and IOP, Aqueous flare, complete vision loss, bilateral common