Ординатура / Офтальмология / Английские материалы / Visual Fields Examination and Interpretation_Walsh_2011

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Figure 2-19. Incongruous homonymous hemianopia.

by branches of the anterior cerebral artery, optokinetic nystagmus (OKN), which is generated in the parietal lobe, can be normal and symmetric after occlusions of the posterior or middle cerebral artery. This gives rise to the observation (“Cogan’s rule”) that a hemianopia with asymmetric OKN suggests a tumor; a hemianopia with symmetric OKN suggests a vascular lesion.

Occipital Lobe. Incongruous field defects rarely occur in the calcarine cortex, except for visual field defects involving or sparing the uniocular temporal crescent of the visual field. Incongruity suggests a lesion elsewhere.

2-4-1-7 Incomplete: Unilateral Sparing of Temporal Crescent. There is a complete homonymous hemianopia sparing the most peripheral visual field of one eye (Figure 2-20).

Posterior Calcarine Cortex. The peripheral temporal visual field of the contralateral eye is represented in the cortex above and below the most anterior portion of the calcarine sulcus anterior to the junction of the parieto-occipital fissure (A) with the calcarine fissure (B). The lesion responsible for a homonymous hemianopia with temporal crescent sparing would anatomically spare the anterior portions of the lingual gyrus (1C) and the precuneus (ID) while injuring the cuneus (1E) and the posterior portion of the lingual gyrus (1C).

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Figure 2-20. Homonymous hemianopia with temporal crescent sparing.

2-4-1-8 Incomplete: Unilateral Defect of Temporal Crescent. In its purest sense, this is a monocular field defect involving the temporal visual field of one eye and could even mimic retinoschisis of the nasal retina. However, many patients with such defects have had or will have other homonymous hemianopic field defects that are binocular (Figure 2-21).

Anterior Calcarine Cortex (1). A lesion of the anterior calcarine cortex may produce a peripheral temporal field defect corresponding to the nasal retina of the contralateral eye. The ipsilateral eye visual field may later become involved as the lesion extends posteriorly. At this time, the true homonymous hemianopic nature of the problem will appear. In the optic radiation, the fibers that will terminate in the anterior calcarine cortex are situated at the upper and lower edges of the superior (A) and inferior (B) bundles, respectively. They terminate in the precuneus (C) superiorly and in the lingual gyrus (D) inferiorly. The arterial supply comes from the posterior cerebral arteries.

2-4-2 Bitemporal Hemianopias

2-4-2-1 Complete. A bitemporal hemianopia is a temporal field defect of each eye (Figure 2-22).

Decussating Fibers of Optic Chiasm (1). The optic chiasm is within the subarachnoid basal cistern. It is surrounded by cerebrospinal fluid. At its posterior margin, the

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Figure 2-21. Homonymous hemianopia minus (a unilateral temporal crescent defect).

optic chiasm indents the third ventricle (A). Anteriorly, it is continuous with the optic nerves that dive toward the optic canals at an angle of approximately 45° from the plane of the diaphragm of the sella. If the dive angle of the optic nerve is more vertical, the optic chiasm is said to be prefixed with regard to the sella; if the angle is more horizontal, the optic chiasm is described as postfixed. One may think of the brain as rotated anteriorly in the former case, while it is rotated posteriorly toward the tentorium cerebelli in the latter case. Because the optic chiasm is usually suspended 1 cm above the posterior two thirds of the diaphragm of the sella turcica, most pituitary tumors (B) must grow about 2 cm above the sella turcica before causing a field defect. Prefixed optic chiasms are associated with optic tract field defects when there is extrasellar extension of pituitary tumors, while postfixed optic chiasms are associated with optic nerve field defects. Miller10 provided a critique of nerve fiber schemata of the optic chiasm.

Because the inferior fibers serve the superior fields, a bitemporal superior quadrantanopia precedes a complete bitemporal hemianopia. The progression is clockwise in the right eye and counterclockwise in the left eye.

Eventually, the defect may involve uncrossed fibers at the lateral aspect of the optic chiasm. A complete bitemporal hemianopia gives no clue as to which surface of the optic chiasm was involved by extrinsic processes first. A bitemporal hemianopia progressing from the inferior to the superior temporal quadrants suggests initial

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Figure 2-22. Complete bitemporal hemianopia. (A) Third ventricle. The arrows represent the progression of the visual field defect associated with the suprasellar extension of a pituitary adenoma (B) from a superior bitemporal quadrantanopia to a complete bitemporal hemianopia.

compression of the superior retinal fibers, as may occur with a craniopharyngioma. Chiasmal visual field defects are caused by tumors, demyelinating disorders, trauma, and other conditions.

2-4-2-2 With Central Depression, Scotomatous. In this pattern, the field defect is similar to a bilateral centrocecal scotoma but does not involve any aspect of the visual field nasal to fixation. The visual acuity may be normal (Figure 2-23A).

Nasal Portions of Both Maculas (1). Binocular macular lesions are unlikely to have a sharp vertical border through the point of fixation.

Optic Chiasm Fibers from the nasal portions of both eyes cross throughout the optic chiasm (2). Incomplete, diffuse, or posterior lesions may most affect the smallerdiameter macular fibers, causing incomplete central hemianopic depressions, which are best detected with minimal-stimulus contrast targets. The sharp vertical line through fixation is diagnostic.

Since the macular fibers are especially dense in the posterior region of the optic chiasm, this field defect is even more apt to happen when pituitary tumors occur with a prefixed optic chiasm or when the third ventricle is enlarged, as in hydrocephalus. When the optic chiasm is prefixed, the intracranial portions of the

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A B

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Figure 2-23. (A) Bitemporal hemianopia with central depression, scotomatous. (B) Relationship of the optic chiasm to the turcica, lateral view.

optic nerves are relatively short and the optic chiasm lies closer to the diaphragm of the sella turcica: The optic chiasm is said to be prefixed if the anterior portion of the optic chiasm covers the tuberculum sellae (A). This occurs in 5% of patients. The optic chiasm is above the center of the sella turcica (B) in 12% of patients. In 79% of patients, it is above the posterior half of the sella turcica. In 4% of patients, the intracranial portions of the optic nerves are relatively long and the optic chiasm is above the dorsum sella (C). In such patients, the optic chiasm is said to be postfixed, and pituitary adenomas must grow a considerable distance beyond the diaphragm of the sella turcica to involve the optic chiasm (Figure 2-23B).

2-4-3 Binasal Field Defects

2-4-3-1 Complete. In this pattern, the field defect involves the entire area nasal to fixation in each eye (Figure 2-24).

Nondecussating Fibers of Optic Chiasm (1). The optic nerve fibers serving the temporal retina and the nasal visual field of each eye do not cross and are in the lateral portion of the optic chiasm. The sharp vertical division of the field at the fovea implicates the nondecussating fibers of the optic chiasm. Binasal hemianopiç visual field defects are rare and may be the result of fusiform, dolichoectatic, sclerotic, or aneurysmal enlargement of one or both internal carotid arteries (A), which lie lateral to the optic chiasm. The optic chiasm becomes trapped between the dilated

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Figure 2-24. Complete binasal hemianopia.

internal carotid and anterior cerebral arteries lying in the anterior optic chiasmal notch. These are rarely pure nasal hemianopias. Usually, the defects blend with those of one optic nerve (B) or of one optic tract (C) (junctional scotoma).

2-4-3-2 Incomplete. These field defects involve a portion of the nasal visual field in each eye. It is rare for them to be completely symmetric (Figure 2-25). Bitemporal Retinas (1). The nasal fields may be depressed, often asymmetrically, in disorders of the peripheral retina.

Optic Nerve Head (2). Glaucomatous visual fields involve the nasal portions of the visual fields first.

Optic Nerve (3). Compression of the superolateral surfaces of the optic nerves against the anterior communicating artery and the A-1 segments of the anterior cerebral arteries (A) may occur when there are aneurysms or rarely as a result of expanding sellar tumors. More often than not, these vessels are stretched over the optic chiasm, rather than over the optic nerves.

Optic Chiasm (4). Binasal field defects resulting from optic chiasmal lesions are much rarer than binasal defects resulting from retinal or optic nerve head disorders (see Section 2-4-3-1). Optochiasmic arachnoiditis may also cause a binasal hemianopia. Dilation of the third ventricle (B) may be accompanied by stretching of the lateral aspect of the optic chiasm. This may explain the binasal hemianopia seen occasionally in patients with hydrocephalus.

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Figure 2-25. Incomplete binasal hemianopia.

2-4-4 Altitudinal Field Defects

2-4-4-1 Noncongruous Binocular and Monocular. Because noncongruous binocular altitudinal visual field defects can arise as a result of separate processes in each eye and in the anterior visual pathway, monocular altitudinal visual field defects are also considered in this section. Monocular disease may lead to a symmetric or an asymmetric loss of all or part of the superior and/or inferior visual field of each eye.

Retina (1). While the most significant retinal cause of altitudinal field loss is an embolism to the superior or inferior branch retinal artery of one eye, there is little likelihood of almost symmetric bilateral lesions without other evidence of stroke. The most common retinal causes of noncongruous altitudinal defects are disorders of the retina such as bilateral rhegmatogenous detachments or bilateral exudative detachments as seen in Harada disease. Disorders that do not directly involve the inner retinal layers may have field defects with sloped margins. Altitudinal visual field defects with step margins may result from the absence of retina, as occurs in inferior colobomas (Figure 2-26).

Optic Nerve Head (2). The short posterior ciliary arteries supply most of the optic nerve head. Occlusion of the short posterior ciliary arteries can cause altitudinal field defects in each eye and may be the presenting symptom of anterior ischemic

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Figure 2-26. Noncongruous altitudinal hemianopia.

optic neuropathy. Bilateral optic nerve head colobomas cause superior altitudinal field defects. Far-advanced glaucoma could mimic bilateral altitudinal field defects if each eye had a large nasal step and breakthrough from the blind spot to the temporal periphery. An apparent altitudinal defect found on a central visual field examination should be further examined with peripheral testing to be certain that it is not a nerve fiber bundle defect breaking through to the periphery. Automated perimetry incorporates altitudinal hemifield comparisons to test for threshold asymmetries above and below the horizontal meridian as well as losses that are symmetric around the horizontal meridian. Bilateral optic nerve head drusen may also cause altitudinal visual field defects.

Optic Nerve (3). While most adult-acquired altitudinal visual field defects were thought to result from anterior ischemic optic neuropathy and other vascular causes, it is now known that approximately 20% of persons presenting with optic neuritis have altitudinal or other nerve fiber bundle defects.11 Contusions of both optic nerves of the optic chiasm produce altitudinal visual field defects. Intracranial tumors and aneurysms of the anterior cerebral and communicating arteries may compress the upper surfaces of both optic nerves.

2-4-4-2 Congruous. Altitudinal hemianopias may symmetrically involve either the superior or the inferior visual fields, with or without macular sparing

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Figure 2-27. Congruous altitudinal hemianopia.

(Figure 2-27). Clinical observations in humans and neurophysiologic studies in monkeys have revealed distinct symptom patterns depending on whether the lesion involves the inferior portions of the occipital lobes, the adjacent temporal lobes or the superior portions of the occipital lobes, and the adjacent parietal lobes. In addition to causing bilateral superior altitudinal hemianopia, bilateral infarcts of the inferior occipital and medial temporal lobes (including the fusiform and lingual gyri) can be associated with dyschromatopsia or achromatopsia of the remaining inferior hemifields so that the patient may demonstrate impaired color vision. The color vision function corresponds to monkey cortical area V4 (see Figure 2-6). Lesions in the inferomedial temporal lobes may also produce impairment of contrast sensitivity and form vision.12,13 A unilateral lesion of one inferior occipital lobe and adjacent temporal lobe may produce a contralateral superior quadrantanopia and a contralateral inferior quadrant dyschromatopsia.

Conversely, patients with inferior altitudinal visual field defects resulting from bilateral superior occipital and adjacent parietal lobe lesions may also have simultanagnosia, manifested by problems in visual/spatial processing and attention.14

Bilateral Superior or Inferior Calcarine Cortex (1). Occlusion of the calcarine branches

(A) of both posterior cerebral arteries can produce a congruous altitudinal