Ординатура / Офтальмология / Английские материалы / Field of Vision A Manual and Atlas of Perimetry_Barton, Benatar_2003

DISCUSSION

Field description: Congruous right inferior quadrantanopia plus, with sparing of the monocular temporal crescent.

Localization: Proximal optic radiation. Pathology: Hypertensive hemorrhage.

Confrontation fields showed the quadrantanopia extending into the upper quadrant, for hand and finger motion.

The field shows high congruity along the superior border of the defect, and clear sparing of the monocular temporal crescent, both features that pointed to a striate lesion (see Case 84). However, MRI (susceptibility sequence) showed a left putaminal/capsular hemorrhage, seen here as the black streak, and thin coronal cuts through the occipital lobe were normal. While striate lesions are probably the most common cause of hemifield defects sparing the monocular temporal crescent, isolated lesions of the optic radiations did cause a similar finding in 3 of 16 patients in a recent series (147).

DISCUSSION

Field description: Congruous partial left homonymous superior quadrantanopia with sparing of the macula and monocular temporal crescent.

Localization: Right striate cortex, inferior bank.

Pathology: Posterior cerebral arterial infarct, posterior temporal branch. Other features: Release hallucinations (see Case 94).

Confrontation fields using hand motion showed a left hemianopia, with sparing of the macula, temporal crescent, and a zone adjacent to the lower vertical meridian.

Since the temporal field extends over 90° while the nasal field stops at 60°, each hemifield has a region that is seen only by the ipsilateral eye—the monocular temporal crescent. This region is represented in the most anterior 10% of striate cortex. The inferior temporal crescent is spared more often than the superior crescent, implying more frequent selective sparing of the superior rostral calcarine bank (147). The most commonly ordered programs in automated perimetry do not detect sparing of the crescent. A special thresh-

old program that tests only the crescent is needed. Goldmann perimetry, however, provides the best comprehensive picture. Preservation of the temporal crescent most often implies a striate lesion, although it can occur less frequently with lesions of the optic radiations (147) (see Case 83).

The axial FLAIR MRI showed an infarct of the right striate cortex (pale area) sparing the anterior retrosplenial portion within the territory of the posterior cerebral artery. The sagittal T1-weighted image 6 weeks later demonstrates atrophy of the inferior bank of the calcarine cortex (arrow, compare with similar image through other hemisphere).

Onset during straining suggests paradoxical cardiac embolism (148). A transient increase in right-sided pulmonary pressure during a Valsalva maneuver may expose a right-to-left cardiac shunt, allowing a clot to migrate from the venous to the systemic arterial circulation and on to the cerebral arteries. Echocardiography with a saline bubble study will document the shunt, while tests for deep venous thrombosis of the legs or pulmonary embolism may provide evidence of a clot.

DISCUSSION

Field description: Congruous homonymous left inferior quadrantanopia plus, sparing the macula.

Localization: Right superior striate cortex, sparing the occipital pole. Pathology: Posterior cerebral arterial infarct, parieto-occipital branch.

Tangent screen perimetry with a 3-mm white target showed a left inferior quadrantic defect with macular sparing.

The automated fields show very congruous defects: the same perifoveal test spot is spared in the lower left quadrant, and the defect extends just above the horizontal meridian beyond the 10° mark in both eyes. Such congruity points to striate cortex as the most likely site of damage. MRI shows the well-demarcated infarct restricted to striate cortex, and providing precise anatomic correlation with the functional deficit: sparing of the occipital pole (see both axial T2 and sagittal T1 images) and involvement of cortex above the calcarine fissure (seen on sagittal T1 image, arrow).

DISCUSSION

Field description: Congruous left homonymous hemianopia with macular sparing. Localization: Right striate cortex, sparing occipital pole.

Pathology: Posterior cerebral arterial infarct.

Confrontation fields showed congruous left homonymous hemianopia to hand motion.

Hemianopia with sparing of the central 5° is far more common with striate infarction than damage to other retrochiasmal structures. The macular representation lies at the occipital pole, which is a watershed zone between the vascular territories of the posterior and middle cerebral arteries. The exact location of the boundary varies among individu-

als. In those in whom the pole is perfused more by the middle cerebral artery, a posterior cerebral infarct will spare the macula. Because there is so much cortex devoted to central vision, a slight variation in the boundary at the pole will not greatly affect the amount of central vision spared; it always seems to span about 5°.

Previously, macular sparing had been considered an artifact of poor fixation (which it may be with sloppy perimetry) or a result of overlapping receptive fields in the retina (149), but modern neuroimaging has placed the occipital pole watershed explanation at the fore (150,151).

HISTORY AND EXAM

An optometrist found a hemifield defect on a routine examination of this 27-yr-old man. Even on direct questioning, he recalled no symptoms that might have dated its onset.

He had normal visual acuity and color vision. Fundoscopy was normal OD but demonstrated band (bowtie) atrophy OS.

DISCUSSION

Field description: Left homonymous hemianopia with sparing of the central field and monocular temporal crescent.

Localization: Striate cortex, sparing the occipital pole posteriorly and the retrosplenial zone anteriorly.

Pathology: Old posterior cerebral arterial infarction.

Confrontation testing showed a left hemianopia with temporal crescent sparing to hand motion.

The sparing of the macula and monocular temporal crescent indicates pathology in the midzone of the striate cortex on the right and likely explains the patient’s lack of awareness of the visual field defect. Axial T2-weighted MRI (shown) revealed a lesion in the expected location. Note the sparing of the occipital pole (arrowhead) as well as the most

anterior portion of the striate cortex (arrow). The presence of band atrophy on the left suggests a long-standing injury with retrograde trans-synaptic degeneration (117), creating a fundoscopic appearance more associated with optic tract injury.

Why did he not notice this sizable hemianopia? Why had he never had a car accident? We have seen several patients with presumed childhood-onset hemianopia and anosog- nosia—this patient is not unique. It may be that such patients have unconsciously become very proficient at an adaptive strategy of making more saccadic eye movements into their blind hemifield (152,153). It is also postulated that subjects with early onset lesions may have the potential for blindsight (154), a residual visual ability mediated by brain stem and extrastriate regions, without the patient’s awareness (155). Blindsight remains somewhat controversial (156–158). Furthermore, it has yet to be shown that blindsight has any practical impact on the daily behavior of patients.

HISTORY AND EXAM

This 52-yr-old man had resection of a right occipital oligodendroglioma. He had presented with sudden headache from hemorrhage into the tumor. Postoperatively he noted difficulty seeing to the left. He was bumping into objects on that side and had trouble keeping his place on the page while reading. He would get lost occasionally when walk-

ing in the town where he had lived for many years. On examination 7 months after surgery, visual acuity was 20/25 OU, there was no RAPD, and color vision and optic disks were normal. His ability to identify famous faces was impaired, despite good general knowledge. The rest of the neurologic examination was normal.