Neuro-ophthalmology

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4 Neuro-ophthalmology

Anatomy of the Visual Pathway

Optic nerve → chiasm → optic tract → lateral geniculate body → optic radiation → occipital lobe (Figure 4-1)

Optic nerve

composed of 1.2 million nerve fibers; approximately 1.5 mm in diameter, enlarges to 3.5 mm posterior to lamina cribrosa due to myelin sheath; located 3–4 mm from fovea; causes absolute scotoma (blind spot) 15° temporal to fixation and slightly below horizontal meridian; approximately 45-50 mm in length (1 mm intraocular, 25 mm intraorbital, 9 mm intracanalicular, 10–15 mm intracranial) (Figure 4-2); acquires myelin posterior to lamina cribosa

image

Figure 4-2 The 4 portions of the optic nerve. The lengths are given.

(From Sadun AA: Anatomy and physiology. In: Yanoff M, Duker JS (eds) Ophthalmology, 2nd edn. St Louis, Mosby, 2004.)

image

Figure 4-3 Anterior optic nerve. The sheath and the vascular supply to the intraocular and intraorbital portions are shown.

(From Sadun AA: Anatomy and physiology. In: Yanoff M, Duker JS (eds) Ophthalmology, 2nd edn. St Louis, Mosby, 2004.)

Other areas

image

Figure 4-6 Horizontal eye movement pathways.

(From Bajandas FJ, Kline LB: Neuro-Ophthalmology Review Manual. Thorofare, NJ, Slack, 1988.)

Physiology

Testing

Visual Field (VF) Defects (Figure 4-9)

Types

Neurologic VF defects

Eye Movements under Supranuclear Control

Nonoptic reflex systems

integrate eye movements with body movements

Eye Movement Disorders

Horizontal Gaze Palsies

Acquired

Vertical Gaze Abnormalities

Nystagmus

Rhythmic involuntary oscillations of the eyes due to disorder of SEM system. Direction named after fast phase (brain’s attempt to correct problem), even though abnormality is noted with slow phase

Acquired Nystagmus

Pattern helps localize pathology, may have oscillopsia

Cranial Nerve Palsies (FIGURE 4-16)

Oculomotor Nerve (CN 3) Palsy

7 syndromes (Figure 4-17)

Nuclear CN 3 palsy (Figure 4-17, image): extremely rare; contralateral SR paresis and bilateral ptosis; pupil involvement is both or neither
Uncal herniation (see Figure 4-17, image): supratentorial mass may cause uncal herniation compressing CN 3
Posterior communicating artery (PCom or PCA) aneurysm (see Figure 4-17, image): most common nontraumatic, isolated, pupil involving CN 3 palsy; aneurysm at junction of PCom and carotid artery compresses nerve, particularly external parasympathetic pupillomotor fibers; usually painful
Cavernous sinus syndrome (see Figure 4-17, image): associated with multiple CN palsies (3, 4, V1, 6) and Horner’s; CN 3 palsy often partial and pupil sparing; may lead to aberrant regeneration
Orbital syndrome (see Figure 4-17, image): tumor, trauma, pseudotumor, or cellulitis; associated with multiple CN palsies (3, 4, V1, 6), proptosis, chemosis, injection; ON can appear normal, swollen, or atrophic
Pupil-sparing isolated CN 3 palsy (see Figure 4-17, image): small-caliber parasympathetic pupillomotor fibers travel in outer layers of nerve closer to blood supply (but more susceptible to damage by compression); fibers at core of nerve are compromised by ischemia; may explain pupil sparing in 80% of ischemic CN 3 palsies and pupil involved in 95% of compressive CN 3 palsies (trauma, tumor, aneurysm)

image

Figure 4-17 Seven syndromes of CN 3 palsy.

(Copyright Peter K. Kaiser, MD.)