Neurological Diseases of the Eye

Question 1

describe blindness (3)

Answer 1

1. unilateral or bilateral
2. retina/optic nerve/optic chiasm
   -abnormal menace and PLR
   -can’t see bc no info getting in
   -cheaper to rule out! use menace and PLR
3. contralateral prosencephalon
   -abnormal menace, normal PLR
   -can’t see because can’t process info

Question 2

describe blindness due to retina/optic nerve/optic chiasm (5)

Answer 2

1. abnormal menace and PLR
2. blind (most common owner complaint)
3. mydriasis
4. absent menace (with normal CN VII/palpebral)
5. absent PLR

rule out retinal causes first! with fundic exam and electroretinogram

Question 3

what are optic chiasm causes of blindness?

Answer 3

1. MUE
2. neoplasia

need an MRI for this but if bilateral, retina or optic nerves are much more commonly affected than optic chiasm

Question 4

what are optic nerve causes of blindness?

Answer 4

1. most common disease: optic neuritis
   -typically non-infectious/immune-mediated (MUE)
   -large breeds can get immune-mediated (NO MUE)
2. sometimes neoplasia
3. as always, can’t easily tell these apart without MRI

Question 5

describe presumptive diagnosis of optic neuritis

Answer 5

1. compatible clinical presentation
   -acute onset
   -any breed
   -median age: 6 years
   -bilateral more common (80%)
2. optic nerve head elevation: can’t tell inflammation from neoplasia though
3. infectious disease testing (very uncommon though)

Question 6

describe definitive diagnosis of optic neuritis/retinal causes of blindness

Answer 6

retina: if fundic exam normal, electroretinogram before MRI
-ensure is not retina before go hunting for optic neuritis

optic neuritis:
1. MRI:
-swelling of optic nerve(s)/loss of CSF around nerves
-+/- multifocal, asymmetrical brain lesions in cases of MUE

2. CSF: mononuclear pleocytosis
3. negative infectious disease titers

Question 7

describe treatment and prognosis of optic neuritis

Answer 7

1. prednisone: 1-2 mg/kg/day, slow taper
2. antimicrobials while waiting for titers?
   -not if fungal suspect
3. dogs with MUE may need long term treatment

prognosis:
-14% regained partial vision
-16% regained complete vision

Question 8

describe internal ophthalmoplegia

Answer 8

1. disease of parasympathetic of CN III
   -mydriasis
   -abnormal PLR: cannot constrict affected pupil, unaffected pupil will constrict with light in either eye
   -visual: normal menace

-don’t forget iris atrophy!

2. unilateral: structural disease
3. unilateral or bilateral: head trauma
4. bilateral
   -ivermectin toxicity
   -thiamine deficiency

Question 9

describe unilateral CN III lesion/parasympathetic/internal opthalmoplegia (2 etiologies, diagnostics, and treatment options) also what else might you see if CN III is affected?

Answer 9

etiologies:
1. neoplasia most common
2. rarely idiopathic/neuritis

diagnostic:
3. recommend MRI!

treatment options:
1. palliative
2. surgery
3. radiation: 18-28 month survival

if CN III affected, might also see
1. ispilateral ptosis: levator palpebrae superioris is innervated by CN III (NOT on exam)

Question 10

describe strabismus/opthalmoplegia

Answer 10

1. lesion of CN III innervates somatic extraocular eye muscles
   -ipsilateral fixed ventrolateral strabismus
   -lack of adduction/medial movement
2. lesion of CN 6: medial strabismus
3. lesion of CN 4: extorsion of eye (rare)
4. external opthalmoplegia
   -paralysis of extraocular muscles
   -lack of physiologic nystagmus
5. commonly affect all nerves together:
   -no deviation of the eye
   -no movement of the eye
6. cavernous sinus syndrome: tumor here affects 3, 4, 5 CN going to eye
7. retrobulbar disease more common: neoplasia, abscess

Question 11

describe extraocular myositis

Answer 11

1. RARE
2. immune-mediated inflammation of extraocular eye muscles
3. young large and giant breeds
4. exophthalmos +/- painful
5. treat with immunosuppressive steroids

Question 12

describe Horner syndrome

Answer 12

1. loss of sympathetic innervation to the eye
2. miosis, ptosis, enophthalmos, third eyelid elevation (passive due to enophthalmos)
   -remember! if just have a miotic pupil, could just be pain! esp if don’t see other horner signs
3. common causes:
   -otitis media/interna: sometimes Horner is the ONLY sign of OMI!!
   -neoplasia anywhere along pathway
   -idiopathic: golden retrievers esp

Question 13

describe the pathway of sympathetics to eye (just for context)

Answer 13

pathway of sympathetics to the eye (for context, not memorize); disease anywhere along this pathway can cause Horner’s!
-cervical spinal cord
-T1-T3
-brachial plexus: in thoracic cavity for some time!!
-vagosympathetic trunk
-tympanic bulla
-eye

Question 14

describe diagnostic workup of Horner syndrome

Question 15

describe how to decide what eye is normal versus abnormal