A. Cranial Nerve II (Optic Nerve)

1. Direct Extension of the brain - fibers myelinated by oligodendrocytes (not Schwann Cells)
2. Lesions of Optic Nerve lead to monocular visual field defect (same as retina)
3. Lesions of optic chiasm
   1. Characteristically lead to bitemporal field defects (hemianopsia)
   2. Seen most often in cavernous sinus syndromes
   3. Examples: pituitary adenomas, Cavernous Sinus Hemorrhage
4. Lesions posterior to optic chiasm
   1. Most lesions (post-geniculate) cause homonymous, hemianoptic defect
   2. Pre-geniculate lesions will not by strictly homonymous
5. Lesions in striae cortex cause homonymous visual field defects (on visual field testing):
   1. Same shape in both eyes
   2. Same position in both eyes
6. Signs / Symptoms
   1. Visual Loss is major problem
   2. Strabismus (wandering eye) - detected using cover test
   3. Afferent pupillary defect will occur in unilateral disease
   4. Pain
   5. Signs and symptoms of more extensive CNS involvement are common

B. Cranial Nerve III (Oculomotor) [2]

1. Actions
   1. Innervates medial rectus, superior rectus, inferior rectus, inferior oblique muscles
   2. Controls pupillary constriction (parasympathetic)
   3. Responsible for lid raising (Levator palpebrae muscles)
2. Symptoms of III Lesion
   1. Pupil down and out; cannot move eye medially past midline
   2. Pupil enlarged - mydriasis (pupillary asymmetry)
   3. Lid droop - ptosis
   4. Nearly all CN III lesions will lead to some DIPLOPIA due to inability to focus
3. Usual Causes
   1. Aneurysm in the posterior communicating artery
   2. Frequently seen in diabetics
4. Unusual causes
   1. These lesions occur in neurons proximal to the cranial nerves (thus, "supranuclear")
   2. Pseudobulbar palsey
   3. Progressive supranuclear palsey

C. Cranial Nerve IV (Trochlear)

1. Action: innervates superior oblique muscle which pulls eye down and in
2. Symptoms of IV Lesion
   1. Patient cannot move eyes down and in well
   2. Head may be tilted to maintain alignemnet of visual input
3. Typical Causes of IV Lesion
   1. Long course dorsally over the midbrain
   2. Particularly susceptible to trauma
4. Isolated CN IV lesions are extremely rare

D. Cranial Nerve VI (Abducens)

1. Action: innervates lateral rectus muscle, which pulls eye laterally
2. Symptoms of VI Lesion
   1. Pupil held medially, cannot pass midline towards lateral
   2. Head often held slightly sideways
3. Usual causes
   1. Long course from pons
   2. Unilateral or bilateral CN VI palseys usually due to increased intracranial pressure

E. Sympathetic Lesions

1. Called Horner Syndrome [2]
2. Types
   1. Congenital - usually attributed to trauma
   2. Acquired - benign and malignant etiologies
3. Signs
   1. 1-2mm Ptosis
   2. Meiosis
   3. Anhidrosis

F. Nystagmus [1]

1. Not a true ocular neuromuscular disorder
2. Occurs due to abnormal vestibular function or vestibular-ocular communication
3. Composed of "fast" and "slow" components
4. Derived from vestibulo-ocular connections
5. Vestibular stimulation leads to slow eye movement in weak direction
6. Rapid cortical correction (fast jerk response) follows slow movement
7. Vertical, horizontal, rotatory, or oscillatory "see-saw" nystagmus
8. Saccades or Pursuit or Spontaneous Nystagmus depends on visual motion input
9. Spontaneous nystagmus is always abnormal except when follows regional head and/or body motion
10. Fast component is accentuated by voluntary eye deviation to that side

G. Cavernous Sinus Thrombosis

1. Usually secondary to oculonasal infections
2. Syndrome
   1. Orbital edema with eye pain, tenderness on palpation
   2. Chemosis, cyanosis of upper face present
   3. Venous congestion
   4. Palsy of CN III, IV, V(3), and VI
3. Patient appears acutely ill
   1. High fever
   2. Headache
   3. Nausea and vomiting
4. Additional Ophthalmic Symptoms
   1. Ophthalmoplegia
   2. Pupuillary changes
   3. Retinal hemorrhages
   4. Papilledema
   5. Sensory changes in ophthalmic division (3) of CN V
5. CSF usually normal unless associated meningitis or subdural empyema
6. Differentiate from mucormycetes infection, usually in diabetics or immunosuppressed
7. Treatment with potent anti-staphylococcal and anti-anaerobic antibiotics
8. Anticoagulation usually of minimal benefit

References

1. Simon JW and Kaw P. 2001. Am Fam Phys. 64(4):623
2. Miller NR and Newman NJ. 2004. Lancet. 364(9450):2045