Interpreting the multifocal visual evoked potential: the effects of refractive errors, cataracts, and fixation errors.

AIM: To understand how refractive errors, cataracts, and fixation errors affect multifocal visual evoked potential (mfVEP) responses. METHODS: Monocular mfVEP responses were obtained using a pattern reversal dartboard display. For the control condition, visual acuity was corrected to > or =20/20 and foveal fixation was maintained. The right eye was tested under the following conditions: simulated refractive error, simulated cataract, steady eccentric fixation, and unsteady fixation. RESULTS: No subject demonstrated significant abnormalities under control conditions. For the simulated refractive error condition, significant centrally located abnormalities were seen for all subjects. For the simulated cataract condition, significant abnormalities were found for three subjects. The steady eccentric fixation condition yielded abnormalities in both eyes for all subjects while the unsteady fixation condition yielded significant central abnormalities in the tested eye. With eccentric and unsteady fixation conditions, all subjects had at least one sector with a waveform polarity reversal. CONCLUSIONS: While the mfVEP is a useful tool for identifying local optic nerve damage or ruling out non-organic aetiology of visual field defects, factors such as uncorrected refractive errors, cataract, eccentric fixation, and unsteady fixation can produce apparent field defects on the mfVEP. With care, these problems can be correctly identified.

Dissociated vertical nystagmus and internuclear ophthalmoplegia from a midbrain infarction.

We describe a patient with a dissociated vertical nystagmus and an internuclear ophthalmoplegia. The vertical nystagmus consisted of a left downward nystagmus with a synchronous right intorting nystagmus when the patient looked down and to the left. This rare type of nystagmus has been described both in isolation and in association with an internuclear ophthalmoplegia. Previous authors postulated a lesion in the midbrain in the region of the medial longitudinal fasciculus. In our patient, a discrete midbrain infarction was demonstrated on magnetic resonance imaging in the hypothesized location, thus providing supportive anatomical evidence for a vertical gaze coordination pathway in the region of the medial longitudinal fasciculus.

Wallenberg's lateral medullary syndrome. Clinical-magnetic resonance imaging correlations.

OBJECTIVE: To correlate clinical and radiologic findings in patients with lateral medullary infarction. DESIGN: Case series with "blinded" evaluation of brain imaging. SETTING: Hospitalized and ambulatory patients at the Neurological Institute of New York (NY). PATIENTS: Thirty-three consecutive patients with lateral medullary syndrome were evaluated by the Stroke Center between 1983 and 1989. RESULTS: Ataxia (70%), numbness either of the ipsilateral face or of the contralateral body (64%), vertigo (51%), and dysphagia (51%) were the most frequent symptoms at onset. Eleven patients had ocular symptoms (diplopia or blurred vision). Horner's syndrome was found in 91%, ipsilateral ataxia in 85%, and contralateral hypalgesia in 85%. Nystagmus (61%) and facial weakness (42%) were less frequent. Head computed tomography was abnormal only when a cerebellar infarction was present (three cases). Magnetic resonance imaging, obtained in 22 cases, was normal in two; a lateral medullary infarction alone was present in 12, and a lesion extending beyond the lateral medulla was found in eight. No correlation was noted between facial weakness or ocular symptoms and infarction extending beyond the lateral medullary region. Vertebral artery disease was confirmed by vascular imaging or insonation studies in 73% of patients. CONCLUSIONS: The triad of Horner's syndrome, ipsilateral ataxia, and contralateral hypalgesia will clinically identify patients with lateral medullary infarction. Facial weakness and ocular symptoms are frequent and do not necessarily imply that the infarction extends beyond the lateral medulla. Cerebellar infarcts only infrequently accompany lateral medullary syndrome, suggesting that most of the posterior inferior cerebellar artery territory is spared, despite the high frequency of vertebral artery occlusion.

Mitochondrial DNA mutations in an outbreak of optic neuropathy in Cuba.

Since October 1991, nearly 51,000 Cubans have been afflicted in an outbreak of optic and peripheral neuropathies. To begin an investigation of the possible role of mitochondrial DNA (mtDNA) mutations in the outbreak, we studied mtDNA from 14 affected and two unaffected Cubans for the 12 mutations associated with Leber's hereditary optic neuropathy. Eleven probands (12 patients) had optic neuropathy and two had peripheral neuropathy only. We also studied two unaffected relatives of one proband. We identified two mtDNA mutations, at nucleotides 11778 and 3460, in two of the 11 probands with optic neuropathy. Although this data set is too small to reach statistically valid conclusions, it does suggest that mtDNA mutations might be contributing to the outbreak of optic neuropathy in Cuba.

Clinical course of a cohort in the Cuban epidemic optic and peripheral neuropathy.

Nearly 51,000 Cubans were afflicted during an outbreak of an optic neuropathy (ON) and peripheral neuropathy (PN) between 1991 and 1993. We re-examined 14 of 20 affected individuals 16 months after an initial evaluation. The optic features were painless symmetric vision loss with poor visual acuity, color vision loss, central or cecocentral scotoma, optic disc pallor, and nerve fiber layer drop-out. The neurologic symptoms included stocking-glove sensory changes, hearing loss, leg cramps, sensory ataxia, hyperactive or absent reflexes, and complaints of memory loss. Two of 11 ON probands tested harbored Leber's hereditary optic neuropathy (LHON)-associated mitochondrial DNA mutations. All patients had received multivitamin therapy. We performed comparisons using the paired two-tailed t test. On re-examination, 12 of 14 patients demonstrated improvement. One patient remained unchanged. One woman with the nt-3460 mtDNA mutation showed a decline in vision. In patients not harboring mtDNA mutations, overall visual acuity, color vision, and peripheral neuropathy manifestations improved significantly (p < 0.001 for each manifestation). Most of the patients with Cuban ON and PN improved on multivitamin therapy. The significance of the mtDNA mutations is unclear. In the 2 LHON patients, manifestation of the disease may have been precipitated by nutritional deficiency. Patients with poor recovery or further deterioration should be evaluated for other factors, including poor vitamin therapy compliance and alternative diagnoses.

Neurolymphomatosis: a clinicopathologic syndrome re-emerges.

We describe a patient with sensorimotor peripheral neuropathy and cranial neuropathy due to autopsy-proven neurolymphomatosis defined by infiltration of peripheral nerves by tumor cells and review the findings in 39 previously reported patients. The cause of the neuropathy is not known. The association with immune-deficient states suggests virally mediated pathogenesis, possibly a retrovirus.

Tracking the recovery of local optic nerve function after optic neuritis: a multifocal VEP study.

PURPOSE: To explore the multifocal visual evoked potential (mVEP) as a technique for tracking local optic nerve damage after unilateral optic neuritis (ON). METHODS: Humphrey visual fields and mVEP recordings were obtained from three patients within 7 days of an episode of ON. Patients were retested during the recovery phase, approximately 4 to 7 weeks later. The multi-input procedure of Sutter was used to obtain 60 local VEP responses (the mVEP) to a scaled checkerboard pattern. The mVEPs were recorded separately for monocular stimulation of both eyes. RESULTS: Initially, all three patients had extensive visual field defects, reduced visual acuity, and depressed mVEP amplitude in regions of poor visual field sensitivity. By 4 to 7 weeks, the fields recovered to near normal sensitivity in most locations, and visual acuity returned to 20/20. The mVEP recovered to nearly full amplitude in all regions, but substantial delays were present in many locations. The delayed responses were associated with regions of visual field loss documented during the acute phase. CONCLUSIONS: The mVEP can be used to track local optic nerve damage after unilateral ON. This technique should be useful in observing the effects of treatments as well as in testing hypotheses about the mechanisms underlying both the acute loss of vision and the subsequent recovery.

An attempt to detect glaucomatous damage to the inner retina with the multifocal ERG.

PURPOSE: To detect glaucomatous damage to the inner retina using the multifocal electroretinogram (mERG). METHODS: The stimulus array consisted of 103 hexagons with a mean luminance of 100 cd/m2 and a contrast of 50%. The mERG was recorded from 13 control subjects, 18 patients with open-angle glaucoma (OAG), 4 glaucoma suspects, and one patient with ischemic optic neuropathy (ION). Individual responses, as well as responses summed within quadrants or across the entire array, were measured in a number of ways. Humphrey visual fields were obtained for all patients, and the mean total deviation (MD) values for the 18 patients with OAG ranged from -2.2 to -18.2 with a mean (SD) of -7.3 (4.5). RESULTS: The mERG measure that best discriminated between the patients and the control subjects was the ratio of the amplitude at 8 msec after the peak response to the amplitude at the peak. Although the value of this ratio fell below the median of the control group for 16 of the 18 OAG patients, only 6 of these patients had ratios that fell below the normal range. Other measures of first- and second-order kernels did not do as well. Both within and across patients, the correlation between local field loss and the mERG ratio measure was poor. Furthermore, although in some patients the mERG waveform is clearly different from normal, in other patients (including the patient with ION) the waveform approximates the normal even in visual field areas with substantial sensitivity loss. CONCLUSIONS: Because glaucomatous damage is known to affect the ganglion cell axon, these data suggest that damage to ganglion cell axons is not a sufficient condition to produce changes in the mERG as measured here and that in patients with clear changes in mERG waveforms, these changes do not appear to be well localized and local waveforms are poorly correlated with local changes in field sensitivity.

An interocular comparison of the multifocal VEP: a possible technique for detecting local damage to the optic nerve.

PURPOSE: To develop a quantitative measure of local damage to the ganglion cells/optic nerve based on an interocular comparison of multifocal visual evoked potentials (mVEP). METHODS: Multifocal VEPs were recorded from both eyes of six normal subjects and four patients; each eye was stimulated separately. Two of the patients had glaucoma, one had ischemic optic neuropathy, and one had unilateral optic neuritis. All four patients had considerably more damage in one eye than in the other, as indicated by their Humphrey visual fields. The multi-input procedure of Sutter was used to obtain 60 VEP responses to a scaled checkerboard pattern. The amplitude in each response was obtained using a root mean square measure of response magnitude. For each of the 60 pairs of responses, a ratio between the amplitude of the responses from the two eyes was obtained as a measure of the relative health of one eye compared with the other. The mean and SD of this ratio measure for the control group were used to specify confidence intervals for each of the 60 locations. All patients had Humphrey 24-2 visual fields performed. To allow a comparison of the mVEPs to the visual fields, a procedure was developed for displaying the results of both tests on a common set of coordinates. RESULTS: Except for a small interocular difference in timing attributable to nasotemporal retinal differences, the pairs of mVEP responses from the two eyes of the control subjects were essentially identical. Many of the pairs of responses from the patients were significantly different. In general, there was reasonably good agreement with the Humphrey 24-2 visual field data. Although some regions with visual field defects were not detected in the mVEP due to small responses from the better eye, other abnormalities were detected that were hard to discern in the visual fields. CONCLUSIONS: Local monocular damage to the ganglion cell/optic nerve can be quantitatively measured by an interocular comparison of the mVEP.

Immunofluorescent studies of the eye in Waldenström's macroglobulinemia.

The eyes of a 53-year-old woman with K light chain macroglobulinemia were studied histopathologically. Retinal hemorrhages were observed on gross examination. Microscopic examination disclosed eosinophilic, PAS-positive deposits in cystoid spaces within the outer plexiform layer, in the inner retina, and about photoreceptors. Immunofluorescent studies showed that the deposits contained IgM. Aneurysmal dilations of small retina vessels were demonstrated as well.

Amaurosis fugax at downward gaze.

A 54-year-old man with a past history of hypertension, diabetes mellitus, hypercholesterolemia and two myocardial infarctions presented with repeated attacks of amaurosis fugax in the right eye. The fact that the amaurosis occurred only on downward gaze is sufficient evidence to exclude carotid atheromatous disease and to imply an orbital etiology.

Visual function improvement in patients with macroprolactinomas treated with bromocriptine.

We studied eight patients who had visual field defects secondary to prolactin-secreting macroadenomas and who had improved visual function with bromocriptine treatment without surgery or radiation. We recommend bromocriptine as a primary treatment for prolactin-secreting macroadenomas. If therapy is effective, continued regular neuro-ophthalmologic, endocrine, and imaging studies are necessary, because treatment with bromocriptine must be continued indefinitely.

Varicella-zoster virus retrobulbar optic neuritis in a patient with human immunodeficiency virus.

PURPOSE: To determine the cause of bilateral retrobulbar optic neuritis followed by progressive outer retinal necrosis in a patient with human immunodeficiency virus (HIV). METHODS: Extensive ophthalmologic, neurologic, infectious disease, rheumatologic, and radiologic examinations were performed. RESULTS: Cerebrospinal fluid samples taken after the onset of bilateral retrobulbar optic neuritis and before the development of clinical progressive outer retinal necrosis disclosed varicella-zoster virus from polymerase chain reaction and viral culture. CONCLUSION: Ophthalmologists and neurologists should consider varicella-zoster virus optic neuritis as a potential precursor of progressive outer retinal necrosis and as a cause of retrobulbar optic neuritis in patients infected with HIV.

Magnetic resonance imaging of optic tract involvement in multiple sclerosis.

We studied two cases of optic tract involvement in multiple sclerosis with documentation by magnetic resonance imaging. In one, incongruous homonymous hemianopsia was accompanied by a decrease in visual acuity in one eye from chiasmal involvement. In the other, the involvement was restricted to the optic tract and the homonymous hemianoptic visual field defect was nearly congruous.

Neuro-ophthalmic complications of intracranial catheters.

We report four patients who sustained direct injury to the brain after insertion of intraventricular shunts and pressure monitoring lines, which resulted in permanent neuro-ophthalmic deficits. These included hemianopsia from an optic tract lesion, esotropia and residual bilateral facial paresis from dorsal pontine injury, unilateral blindness from damage to the optic nerve, and dorsal midbrain syndrome from catheter compression in the region of the posterior commissure. Although presumably rare, such injuries should be considered in diagnosing patients with neuro-ophthalmic complaints after insertion of such devices.

Visual paraneoplastic syndrome associated with undifferentiated endometrial carcinoma.

We report a case of visual paraneoplastic syndrome associated with undifferentiated endometrial carcinoma. This syndrome has not previously been reported with this type of tumour; it has occurred most often with small-cell carcinoma of the lung. Electroretinography and histopathological examination have consistently shown the site of injury to be the outer retina. We review the findings in the reported cases and the proposed causes of the loss of vision in this condition.

The sleep test for myasthenia gravis. A safe alternative to Tensilon.

The diagnosis of myasthenia gravis is usually confirmed by a Tensilon test, which can be complicated by cholinergic side effects that include cardiopulmonary arrest. An alternative, the Sleep test, based on the characteristic of myasthenia that symptoms and signs worsen with fatigue and improve after a period of rest, is safe, moderately sensitive, and specific. The diagnosis of myasthenia can be confirmed by observing resolution of ptosis or ophthalmoparesis immediately after a 30-minute period of sleep; the reappearance of the myasthenic signs over the next 30 seconds to 5 minutes adds further confirmation.