Ординатура / Офтальмология / Английские материалы / Neuro-Ophthalmology_Kidd, Newman, Biousse_2008
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1Neuro-Ophthalmologic Anatomy
and Examination Techniques
STEVEN L. GALETTA LAURA J. BALCER
GRANT T. LIU
Introduction
The Afferent Visual Pathways
Anatomy of the Retina and Optic
Nerve
Disorders of the Retina
Optic Nerve Disease
Anatomy of the Optic Chiasm
Chiasmal Visual Loss
Anatomy of the Retrochiasmal
Visual Pathways
Disorders of the Retrochiasmal
Visual Pathways
The Ocular Motor System
Anatomy of the Orbit and
Extraocular Muscles
Anatomic Considerations of the
Third, Fourth, and Sixth
Cranial Nerves
Orbital Apex and Cavernous
Sinus Syndromes
Anatomy of the Supranuclear,
Internuclear, and Vestibulo-
Ocular Gaze Pathways
Saccade System
Vestibulo-Ocular System
Pursuit System
The Pupillary Pathways
Anatomy of the Pupillary
Pathways
The Neuro-Ophthalmologic
Examination
Visual Acuity
Near Vision
Color Vision
Contrast Sensitivity and Low-
Contrast Letter Acuity
Amsler Grid Testing
Visual Field Testing
Tangent Screen Field Testing
Formal Perimetry
Pupillary Examination
Eyelid Examination
Ocular Motility
Ophthalmoscopy
Neuro-Ophthalmologic Examination in Comatose Patients
Approach to the Comatose Patient
Examination in Comatose Patients
Pupillary Abnormalities in Coma Eye Movement Abnormalities
in Coma
Abnormal Ocular Fundi in Coma Terson’s Syndrome
References
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2Neuro-Ophthalmology: Blue Books of Neurology
Key Points
Certain visual field defects may have exquisite localizing value and may predict the underlying etiology of the lesion.
The five hallmarks of an optic neuropathy are decreased acuity, impaired color vision, an afferent pupillary defect, abnormal visual field, and optic nerve head change.
Vertical diplopia usually results from one of the following: third nerve palsy, fourth nerve palsy, skew deviation, myasthenia gravis, or thyroid eye disease.
The presence of pain with an ocular motility disturbance, pupillary abnormality, or visual loss should raise the possibility of a neuro-ophthalmologic emergency.
Introduction
Neuro-ophthalmologic disorders, affecting the afferent and efferent visual pathways, are often encountered by neurologists in clinical practice. Combining an understanding of neuro-ophthalmologic anatomy with proper examination technique provides a powerful means to detect and localize lesions that involve the visual system. Furthermore, precise documentation of the extent of damage within the visual system is becoming an invaluable method to assess the effect of emerging neurologic therapies. Signs and symptoms of visual pathway dysfunction commonly occur as initial presenting features of potentially treatable neurologic disorders, including strokes, multiple sclerosis, tumors, aneurysms, central nervous system infections, and certain movement disorders. Visual loss and ocular motility disorders may also occur as manifestations of systemic disorders, such as cardiac disease, diabetes mellitus, hypertension, and drug toxicity. Prompt recognition and localization of neuro-ophthalmologic signs and symptoms are crucial to effective diagnosis and management. This chapter focuses on aspects of neuroanatomy and the neuro-ophthalmologic examination that are most important to the diagnosis of afferent and efferent visual pathway lesions.
The Afferent Visual Pathways
ANATOMY OF THE RETINA AND OPTIC NERVE
The retina is the initial sensory structure encountered within the afferent visual pathways and has the distinction of being the only portion of the nervous system that can be directly examined by the clinician. Many neurologic and systemic disorders may be characterized by their retinal findings. The structures of the normal retina and fundus, including the optic disc, macular area, fovea, and retinal arterioles and veins, are shown in Figure 1–1A and B.1
The innermost cellular layer of the retina consists of ganglion cells. Ganglion cell axons travel within the retinal nerve fiber layer and are bundled in a distinct configuration as they approach the optic nerve head.2 Axons that directly enter the temporal aspect of the disc are called the papillomacular bundle and they are derived from the macula and serve central vision. Ganglion cell axons from the
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Arteriole |
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Vein
Optic disc
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Figure 1–1 A, Schematic diagram of normal left fundus. B, Photograph of normal left fundus. (A, Reprinted with permission from Liu GT: Disorders of the eyes and eyelids. In Samuels MA, Feske S (eds): Office Practice of Neurology. New York, Churchill Livingstone, 1996, p 41.)
peripheral field traverse around the papillomacular fibers to form the superior and inferior arcuate bundles. Finally, fibers subserving temporal vision coalesce in a radial pattern to enter the nasal aspect of the disc. Images fall on the retina in an “upside-down and backward” fashion. For example, in the left eye, the upper nasal retina receives information from the lower temporal portion of the visual field, whereas the lower temporal retina receives information from the upper nasal field. This retinotopic organization of visual information is also present within the optic nerve and is preserved throughout the afferent visual pathways.
The blood supply to the retina and optic nerve originates primarily from the ophthalmic artery, the first major intracranial branch of the internal carotid artery. The inner two thirds of the retina is supplied by the central retinal artery (Fig. 1–2).3 This artery travels within the optic nerve for a short distance behind the disc and then branches out to supply the four main quadrants of the retina (Fig. 1–1A and B). The short and long posterior ciliary arteries are also branches of the ophthalmic artery; the long posterior ciliaries supply the ciliary body (responsible for lens accommodation), whereas the short posterior ciliary
4Neuro-Ophthalmology: Blue Books of Neurology
Subarachnoid |
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ciliary Sclera Retina artery
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Anterior and posterior lamina cribrosa
Figure 1–2 Schematic diagram of the optic nerve head demonstrating circulation to the optic nerve head (posterior ciliary arteries) and retina (central retinal artery). (Reprinted with permission from Patten J: Vision, the visual fields and the olfactory nerve. In Neurological Differential Diagnosis, ed 2. New York, Springer-Verlag, 1996, p 23.)
arteries provide the main blood supply to the optic nerve head and the outer one third of the retina. Although the optic disc itself is supplied by a network fed mostly by the posterior ciliary arteries (the anastomotic circle of Zinn-Haller), the portion of the optic nerve directly behind the lamina cribrosa (intraorbital optic nerve) is supplied by perforating branches of the ophthalmic artery.
DISORDERS OF THE RETINA
Visual field loss caused by retinal disorders is characterized by defects that may lack connection to the blind spot and typically do not show “respect” for (tend to extend beyond) the vertical or horizontal meridians. These meridians are important in the interpretation of visual fields; defects that occur in the setting of optic nerve disease tend to demonstrate “respect” for the horizontal meridian because the nerve fibers that enter the optic disc are segregated into superior and inferior arcuate bundles as they traverse the nerve fiber layer of the retina. Visual field defects that arise from chiasmal or retrochiasmal disease show respect for the vertical meridian; this is because of the segregation of nasal and temporal retinal fibers within and beyond the chiasm (Figs. 1–3 and 1–4).4,5
OPTIC NERVE DISEASE |
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The optic nerve is vulnerable to injury |
resulting from increased intracra- |
nial pressure, which may cause swelling |
(papilledema) of both optic discs. |
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Figure 1–3 Lesions of the optic chiasm and their corresponding visual field defects. Note that fibers from the inferior nasal retina (corresponding to the superior temporal visual field) travel briefly within or very close to the contralateral optic nerve; this forward bend of fibers is termed Wilbrand’s knee. The term hemianopsia refers to a visual field defect that respects the vertical meridian; homonymous indicates that the defect involves the same side of the visual field in both eyes; an incongruous defect is that for which the extent of visual field loss is asymmetric between the two eyes. (From Liu GT: Disorders of the eyes and eyelids. In Samuels MA, Feske S (eds): Office Practice of Neurology. New York, Churchill Livingstone, 1996, p 46. Modified from Hoyt WF, Luis O: The primate chiasm. Arch Ophthalmol 1963; 70: 69-85.)
Optic nerve head ischemia, compression of the intraorbital optic nerve, infiltration by tumor, and inflammatory disease may produce optic disc swelling that may be difficult to distinguish from papilledema (swelling resulting from increased intracranial pressure) based on the disc appearance alone. However, although papilledema is most often bilateral, other mechanisms usually produce unilateral disc swelling. Optic atrophy, causing the optic disc to have a pale or white appearance (compared with the normal orange appearance seen in Fig. 1–1A),
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RL
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Location |
Field defect |
1 Left optic nerve
2 Chiasm
3 Right optic tract
4 Left lateral geniculate nucleus
5 Left temporal lobe
6 Left parietal lobe
7 Left occipital lobe (upper bank)
8 Left occipital lobe (lower bank)
9 Right occipital lobe
Left eye Right eye Comment
No light perception left eye
Bitemporal hemianopsia
Incongruous left homonymous hemianopsia
Right homonymous sectoranopia (lateral choroidial artery)
Incongruous right homonymous hemianopia
Right homonymous upper quadrant defect ("pie in the sky")
Right homonymous defect, denser inferiority
Right homonymous lower quadrantanopsia (macular sparing)
Right homonymous upper quadrantanopsia (macular sparing)
Left homonymous hemonymous hemianopia (macular sparing)
Figure 1–4 Lesions of the afferent visual pathway and their corresponding visual field defects. (Reprinted with permission from Liu GT: Disorders of the eyes and eyelids. In Samuels MA, Feske S (eds): Office Practice of Neurology. New York, Churchill Livingstone, 1996, p 43. Modified from Mason C, Kandel ER: Central visual pathways. In Kandel ER, Schwartz JH, Jessell T (eds): Principles of Neural Science, 3rd ed. Norwalk, CT, Appleton & Lange, 1991, p 437.)
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may occur as a late finding in patients with visual loss resulting from untreated papilledema, optic nerve compression, ischemia, tumor infiltration, or inflammation. Visual field defects that are characteristic of early or developed papilledema include enlargement of the blind spot and generalized constriction. Central visual acuity and color vision are generally spared early on in the setting of papilledema.
Ischemic, compressive, infiltrative, or inflammatory causes of optic nerve dysfunction, however, are often associated with altitudinal (involving selectively the upper or lower half of the visual field with respect for the horizontal meridian) or arcuate (radiating from the blind spot but not involving an entire half of the field) visual field defects. Other visual field defects characteristic of optic neuropathies include central scotomas (decreased central vision) and cecocentral scotomas (involving the central vision and blind spot). Patients with compressive, infiltrative, or ischemic optic neuropathies often present with reduced visual acuity; abnormal color vision; an afferent pupillary defect; and, in the case of chronic lesions, optic disc pallor.
ANATOMY OF THE OPTIC CHIASM
Intracranially, the optic nerves join to form the optic chiasm. As shown in Figure 1–3, fibers from the temporal retina remain ipsilateral within the chiasm, whereas fibers from the nasal retina cross within the chiasm to enter the contralateral optic tracts (Fig. 1–5).6 Within the chiasm, the most inferior nasal fibers (representing the superior temporal visual field) travel briefly within or very close to the contralateral optic nerve after crossing over (Fig. 1–3). This forward bend of fibers from the contralateral eye at the anterior chiasm is termed Wilbrand’s knee. Although the existence of Wilbrand’s knee in living primates has been
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Figure 1–5 Relationships of the optic nerves (ON) and chiasm (X) to the sellar structures and third ventricle (3). C, anterior clinoid; D, dorsum sellae; P, pituitary gland in sella. (From Glaser JS, Sadun AA: Anatomy of the visual sensory system. In Glaser JS (ed): Neuro-Ophthalmology, 2nd ed. Philadelphia, JB Lippincott, 1990, p 68.)
8Neuro-Ophthalmology: Blue Books of Neurology
questioned by some authors,7 the concept of this structure remains useful to the understanding of visual field defects that occur in the setting of anterior chiasmal lesions, such as the junctional scotoma (Fig. 1–3).
In most individuals, the optic chiasm is located directly above the sella or pituitary fossa, anterior to the pituitary stalk, and directly inferior to the hypothalamus and third ventricle (Fig. 1–5). The position of the chiasm with respect to the pituitary fossa, however, may be variable, and occasional individuals may have a pre-fixed (main body of the chiasm located anteriorly above the sella) or postfixed chiasm (body of the chiasm located posteriorly above the sella). The chiasm is situated at an upward 45-degree angle above the sella, as shown in Figure 1–5.6
The blood supply to the optic chiasm arises from two sources: (1) the superior hypophyseal arteries (inferiorly), which are fed by the internal carotid, posterior communicating, and posterior cerebral arteries, and (2) branches of the anterior cerebral arteries (superiorly). Because of this collateral blood supply, infarction of the chiasm is extremely rare.
CHIASMAL VISUAL LOSS
Because of the cross-over of nasal retinal fibers within the body of the optic chiasm (Fig. 1–3), compressive and infiltrative lesions in this region usually cause temporal visual field defects in both eyes that respect the vertical meridian (a bitemporal hemianopsia). Common etiologies of chiasmal syndromes in adult patients include pituitary adenoma, craniopharyngioma, meningioma, and aneurysm. The exact characteristics of the visual field defect (Fig. 1–3) depend on the location and extent of chiasmal involvement, as well as the position of the chiasm (pre-fixed or post-fixed) with respect to the sella and third ventricle (Fig. 1–5). The most common defect related to chiasmal disease, the bitemporal hemianopsia, occurs in association with lesions affecting the body (central portion) of the chiasm (Fig. 1–3, visual field #3). Lesions of the anterior chiasm involve both the ipsilateral optic nerve and the crossing fibers derived from the contralateral temporal field; this results in a junctional scotoma, characterized by an ipsilateral central scotoma and a contralateral superior temporal defect (Fig. 1–3, visual field #2). Posterior chiasmal involvement may be associated with bitemporal central hemianopic scotomas (Fig. 1–3, visual field #4). Reduced visual acuity, color vision, and optic atrophy are also characteristic of chiasmal disorders.
Because the optic chiasm is situated above the pituitary sella and below the third ventricle (Fig. 1–5), bitemporal defects affecting mainly the inferior visual fields suggest a lesion arising from the third ventricular region, whereas defects that break out superiorly and temporally usually indicate a lesion arising from the sella. The upward angle of the chiasm above the sella (Fig. 1–5) helps to explain why such field defects occur and why sellar masses, such as pituitary adenomas, must be large to produce chiasmal visual field loss.
ANATOMY OF THE RETROCHIASMAL VISUAL PATHWAYS
The Optic Tracts
Posterior to the chiasm, each optic tract contains fibers originating in the ipsilateral temporal retina and contralateral nasal retina. Fibers of the optic tracts travel
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above and around the infundibulum and below the third ventricle (Fig. 1–4). The majority of the blood supply to the optic tracts derives from branches of the anterior choroidal artery, direct branches of the internal carotid artery, and the posterior communicating artery.2
The Lateral Geniculate Nuclei
The lateral geniculate nuclei of the thalamus (LGN) contain the first post-retinal synapses within the afferent visual pathways. Most of the axons within the optic tracts synapse in the LGN; however, those that subserve the pupillary light reflex pathways branch off of the optic tracts before reaching the LGN, synapsing in the pretectal nuclei of the midbrain. Regions of the LGN are supplied by the anterior choroidal artery (lateral wedges of the LGN), by the posterior choroidal artery (medial wedge), or by an anastomosis of both (middle wedge supplying macular vision).8
The Optic Radiations
After exiting the LGN, geniculocalcarine fibers destined for the calcarine (visual) cortex form the optic radiations. Fibers within the optic radiations separate into superior and inferior bundles, passing within the white matter of the parietal and temporal lobes, respectively (Fig. 1–4). The superior (parietal) fibers carry visual information from the contralateral inferior visual fields, whereas the inferior fibers, traversing forward within the temporal lobe to form Meyer’s loop, subserve the contralateral superior visual fields. The superior optic radiations receive their blood supply from branches of the middle cerebral arteries, whereas the inferior radiations are primarily supplied by branches of the posterior cerebral arteries.
The Occipital Lobes and Calcarine Cortex
The superior (parietal) and inferior (temporal) bundles of the optic radiations project to the upper and lower banks of the calcarine (visual) cortex, respectively, within the occipital lobes. Thus, the upper bank of the calcarine cortex receives information from the contralateral inferior visual fields, whereas the lower bank receives information from the contralateral superior visual fields. This strict retinotopic organization of fibers to the upper and lower banks of the calcarine cortex explains why visual field defects related to occipital lobe lesions may be extremely congruous (symmetric defects in both eyes), respecting both the horizontal and vertical meridians (Fig. 1–4). The macular area is represented in the occipital poles; remarkably, this central 10 degrees of vision encompasses approximately one half of the surface area of the visual cortex.9 The fovea (Fig. 1–1A), or very center of vision, is represented within the tips of the occipital poles. Branches of the posterior cerebral arteries comprise the major blood supply to the calcarine cortex. The occipital poles have a dual blood supply consisting of branches of both the posterior and middle cerebral arteries, providing a basis for macular sparing in the setting of occipital lobe infarcts.
Visual association areas, located in the occipito-temporal and occipito-parietal regions, subserve the functions of higher cortical visual processes, such as object
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recognition (occipito-temporal area), color perception within the contralateral hemifield (lingual and fusiform gyri, area V4), facial recognition (mesial occipitotemporal regions), spatial orientation, and visual attention (parietal lobe).
DISORDERS OF THE RETROCHIASMAL VISUAL PATHWAYS
Optic Tract Lesions
Lesions of the optic tract in isolation are generally not associated with visual acuity loss. However, some optic tract lesions are large and may extend to affect the ipsilateral optic nerve. The characteristic visual field defect in the setting of an optic tract lesion is an incongruous (asymmetric extent of involvement between the two eyes) contralateral homonymous hemianopsia (Fig. 1–4, visual field #3). Patients with optic tract lesions also have an afferent pupillary defect in the eye with the greater extent of visual field loss (usually the eye contralateral to the lesion). A characteristic pattern of optic atrophy is also seen with optic tract disorders; this consists of temporal optic disc pallor ipsilateral to the lesion and “bow tie” atrophy of the contralateral optic disc.
Lateral Geniculate Nuclei Lesions
Unilateral lesions of the LGN and beyond do not affect central visual acuity and are not associated with an afferent pupillary defect unless the optic tract is also involved. Incongruous contralateral homonymous hemianopsias, indistinguishable from those caused by tract lesions, may occur (Fig. 1–4, visual field #4). Given the LGN’s unique dual blood supply (lateral and anterior choroidal arteries), congruous contralateral sectoranopias affecting the lateral wedge in isolation or the upper and lower wedges of the visual field are also encountered (Fig. 1–4, visual field #4).8
Optic Radiation Lesions
Because of the anatomic separation of the optic radiations into inferior (temporal) and superior (parietal) bundles, lesions in these areas cause homonymous hemianopsias affecting predominantly the upper (temporal lobe—“pie-in-the-sky”) or lower (parietal—more dense inferiorly) contralateral visual fields (Fig. 1–4, visual fields #5 and #6). Lesions involving the parietal radiations, or any other retrochiasmal structure, may also produce a dense, complete homonymous hemianopsia (affecting both the upper and lower quadrants). When this defect is encountered, the exact location of the lesion within the retrochiasmal pathways cannot be determined based on the visual field alone.
Occipital Lobe Lesions
Macular sparing (lack of extension of the hemianopsia to the center of fixation) is a unique feature that may occur in the setting of occipital lobe lesions (Fig. 1–4, visual field #9). Occipital lobe-related homonymous hemianopsias, when incomplete, are generally congruous, unlike defects related to the optic tract or LGN. The occipital cortex is also retinotopically organized, such that lesions of the