Optic disc duplication or coloboma?

AIM: To describe lesions resembling optic disc duplication and highlight their unusual visual fields. The authors also report the first case of pseudo-duplication of the optic disc with overlying retinal nerve fibre layer. METHODS: Retrospective, non-comparative review of case notes. Humphrey visual fields and OCT-3 imaging were performed. RESULTS: All 11 cases represented peripapillary chorioretinal coloboma, some of which lie superior to the optic disc. A double blind spot or superior hemifield defects can be demonstrated by automated visual field testing. CONCLUSION: Clinical examination and identification of bridging retinal vessels from the true optic disc to the second pseudo disc can usually avoid unnecessary invasive and non-invasive investigations.

Pseudostereoscopic illusion caused by interhemispheric temporal disparity: clinical and experimental observations.

An extension of Pulfrich's pseudostereoscopic illusion to a situation without interocular disparity, ie, even under purely monocular circumstances, was clinically observed and experimentally produced. The perceived distortion of the movement of a swinging pendulum was found to depend on different combinations of interhemispheric disparity induced by selective prolongation of the conduction time from the nasal or temporal retina to the corresponding hemisphere. In patients, tumor pressure caused the slower conduction time. In normal subjects, neutral density filters covering different visual fields produced similar conduction delays under experimental conditions. Recording the visually evoked response from over each hemisphere provided an objective tool for demonstration and measurement of interhemispheric differences of retinocortical conduction times in various clinical and experimental setups.

Bilateral congenital restriction of upward eye movement.

Neurologic evaluation of a child with a severe headache revealed a bilateral inability to move the eyes above the horizontal plane. Computed tomographic and magnetic resonance scans of the brain obtained for a suspected midbrain lesion were normal. Photographs from early childhood confirmed that the deficit was congenital.

Intracranial optic nerve infarction from subdural hematoma. Clinical and neuropathological findings.

A 60-year-old man fell; a subdural hematoma developed and he lost consciousness. Visual evoked potentials demonstrated a total conduction block in the left optic nerve and slowed conduction on stimulation of the right eye. He died four weeks later, and necropsy showed focal infarcts in the intracranial portion of both optic nerves.

Magnetic resonance imaging of the human lateral geniculate body.

We used magnetic resonance imaging to map the human lateral geniculate body. The optimal imaging plane was determined by obtaining axial and coronal scans in two normal brains obtained at autopsy. The brain specimens were then sectioned and individual slices were compared with matching magnetic resonance images. After the lateral geniculate body was identified using this correlative anatomic approach, the nucleus was imaged in four normal subjects.

Visual-motor adaptation. Quantitative demonstration in patients with posterior fossa involvement.

Short-term visual-motor adaptation to magnifying spectacle lenses was studied in normal subjects and in patients with nonacute posterior fossa lesions. When normal subjects, looking through magnifying lenses, pointed open loop to targets without viewing their hands, they initially underestimated the distance (magnification effect). After a 20-minute close-loop training or adaptation exposure period during which they viewed the performance of their hands, a modified visual-motor scheme evolved, compensating for about half of the lens-induced pointing error (adaptation effect). Removal of the lenses after adaptation caused open-loop, overshooting pointing errors (adaptation after-effect). Four patients with remission of cerebellar signs showed normal visual-motor adaptive performance, evidence of ability to recalibrate gain. One patient with persisting cerebellar ataxia was unable to recalibrate gain during close-loop visual-motor training. His history of transient palatal myoclonus implicates a role for the cerebellar-olivary system in calibration of visual-motor gain.

Metastatic infiltration of nerves in the cavernous sinus.

Painful dysesthesia in association with ocular motor palsies characterized intraneural carcinomatous invasion in a 48-year-old man. Transcranial biopsy of the cavernous sinus stopped the pain; the specimen confirmed the diagnosis and provided the rationale for radiation therapy. One year after treatment, the patient was healthy and pain-free, with improved ocular motor function. The source of the carcinoma remains unknown.

Visually evoked response asymmetries in a family with congenital nystagmus: possible evidence of abnormal visual projections.

Flash-evoked visual responses of two patients from a family with congenital nystagmus showed marked asymmetry between the recordings from the right and left occipital regions in response to monocular stimulation. The asymmetries were crossed, ie, the degree of abnormality inverted when the stimulus changed from one eye to the other. Stimulation of both eyes together evoked symmetrical responses from the two hemispheres. The patients had no signs of abnormality involving the visual pathways. The changes in the visually evoked responses were similar to those found in human albinos, who are known to have abnormal retinostriate projections and also nystagmus.

Midbrain corectopia.

Intermittent corectopia was recently observed in a patient with bilateral, rostral midbrain infarction. Results from neuropathologic examination disclosed isolated but intact Edinger-Westphal nuclei. An explanation of midbrain corectopia centered on segmental innervation of the pupil by the Edinger-Westphal nucleus. In the presence of a paralyzed dilator muscle, select, central inhibition of sphincter tone resulted in an oval and eccentric pupil.

Oculomotor effects of intermittent conduction block in myasthenia gravis and Guillain-Barré syndrome. An oculographic study with computer simulations.

Five abnormal oculographic patterns were identified in eight patients with either myasthenia gravis or Guillain-Barré syndrome (GBS). These could be differentiated into three intrasaccadic and two postsaccadic abnormalities. From our studies of computer simulations, and considering the established pathophysiology of myasthenia gravis and GBS, we believe that our oculographic findings were a consequence of defects in peripheral neural and neuromuscular conduction, together with a simple adaptive increase in duration of the saccadic burst of central innervation. We conclude that the eye movement abnormalities we observed are explained by intermittent block of peripheral conduction, and suggest that any disease causing intermittent blockage of neural signals to extraocular muscles will produce similar abnormalities of eye movement.

Convergence-evoked nystagmus. Congenital and acquired forms.

Pendular nystagmus occurring during binocualr fixation and pursuit of near objects is true convergence-evoked nystagmus. Two forms of this nystagmus are described, one congenital and the other acquired in the course of multiple sclerosis. The congenital form was conjugate and the acquired form disjunctive. Neuropathological examination provided no morphological explanation for the congenital pattern. These two unique forms of nystagmus are induced by one of the visuomotor subsystems controlling convergence.

Isolated congenital hemianopia caused by prenatal injury to the optic radiation.

Isolated congenital hemianopias are typically caused by developmental abnormalities of the occipital lobe cortex. We describe two patients with an incidental partial hemianopia associated with unilateral periventricular leukomalacia that was acquired prenatally. Magnetic resonance imaging scans suggest a late second or early third trimester unilateral cerebral ischemic event.

Painful oculomotor nerve palsy due to dural-cavernous sinus shunt.

Two patients presented with painful unilateral oculomotor nerve palsies without evidence of ocular congestion or hypoxia. They were initially thought to have posterior communicating or distal internal carotid aneurysms, but had, in fact, dural-cavernous sinus shunts, draining posteriorly into the inferior petrosal sinus. One patient later developed a moderately severe congestive ophthalmopathy, and repeated selective carotid arteriograms showed that the shunt was now draining anteriorly into the superior ophthalmic vein. In the other patient, the oculomotor nerve palsy resolved without the development of any further signs. These observations support the concept that dural-cavernous sinus shunts produce symptoms that are dependent on the direction of drainage from the shunt. It is clear that the direction of drainage can change and that thrombosis of the posterior cavernous sinus determines the direction of drainage. The exact mechanism of the cranial neuropathy is, however, unknown.

Does neuroretinitis rule out multiple sclerosis?

Neuroretinitis, a form of optic neuritis, is characterized by papillitis and a stellate macular exudate, or "macular star." The star implies the presence of a disc vasculopathy and secondary leakage of lipoproteinaceous material into the macula. Demyelinating optic neuritis would not be expected to produce a secondary macular exudate. We reviewed the literature on the risk of multiple sclerosis developing in a patient after an attack of optic neuritis, and rarely found a comment on the presence of a macular star. We then reviewed two series of 40 patients who had neuroretinitis and added ten patients of our own. Signs of multiple sclerosis had not developed in the 13 patients contacted retrospectively, nor in the patients followed up prospectively. We also noted that in our patients, neuroretinitis may be accompanied by other neurologic manifestations; neuroretinitis may be bilateral and may be staggered; papillitis may present without a macular star, only to have typical exudates develop up to two weeks later; and the macular exudate may take up to 12 months to resolve. We suggest that patients who demonstrate acute papillitis with a normal macula be reevaluated within two weeks for the development of a macular star. Its presence militates strongly against the subsequent development of multiple sclerosis.

Midbrain myasthenia: fatigable ptosis, 'lid twitch' sign, and ophthalmoparesis from a dorsal midbrain glioma.

A collection of symptoms and signs indistinguishable from ocular myasthenia can be caused by an intracranial mass. We illustrate this condition with the case of an adolescent girl with neurofibromatosis type 1 and a dorsal midbrain astrocytoma. At presentation, she had fatigable ptosis, upgaze paresis, and a positive "lid twitch" sign. Radiation therapy resulted in marked reduction of her signs, confirming that the muscle fatigue was central in origin. We discuss the possible mechanisms of this central fatigability.

Myasthenic abduction mystagmus in a patient with hyperthyroidism.

Intravenous edrophonium chloride promptly stopped a sustained high frequency abduction nystagmus, supporting a diagnosis of myasthenia gravis in a patient with hyperthyroidism. Myasthenia gravis should be considered in the differential diagnosis of any acquired, isolated, and sustained abduction nystagmus, and this possibility should be ruled out by intravenous edrophonium chloride.

Congenital quadrantanopia with occipital lobe ganglioglioma.

A 24-year-old man with recent-onset seizures was found to have an occipital lobe ganglioglioma with homonymous quadrantanopia and trans-synaptic atrophy of retinal nerve fibers. This association indicates that gangliogliomas may arise during neural development and exist for many years before onset of symptoms.

Pathogenesis of acute monocular blindness from leaking anterior communicating artery aneurysms: report of six cases.

This report describes six cases of leaking anterior communicating aneurysms, collected over 37 years, that caused acute monocular blindness. In two cases, surgical and pathologic evidence demonstrated the pathogenic mechanism: As the aneurysm enlarges, the down-pointing dome compresses the optic nerve from above and adheres to it. When the aneurysm ruptures through the adherent dome, it bleeds directly into the optic nerve, resulting in severe headache and monocular blindness. The other cases also suggest an alternative mechanism, namely, direct optic nerve compression by the aneurysm.

Evoked potentials in the evaluation of visual field defects due to chiasmal or retrochiasmal lesions.

We used monocular full-field and hemifield pattern reversal stimulation to study visual evoked potentials (VEPs) in 20 patients with confirmed defects of the visual pathways. In 10 of 12 patients with homonymous field defects, it was possible to lateralize the brain lesion but not to predict the site of the lesion within the hemisphere. In four of eight patients with bitemporal field defects, VEPs suggested involvement at the chiasmal level. In the remaining cases, VEPs provided no correlation with perimetric and radiologic findings. We found that VEPs usually corroborated other diagnostic studies but subtle defects were not detected reliably, and large hemianopic defects were occasionally not lateralized accurately. VEP analysis is therefore of only limited value in assessment for clinical purposes of patients with homonymous or bitemporal hemianopias.

Optic tract atrophy with cerebral arteriovenous malformations: direct and transsynaptic degeneration.

Three patients with postgeniculate cerebral arteriovenous malformations (AVM) had band atrophy of the contralateral optic nerve. One patient had homonymous hemioptic hypoplasia. These cases might have been construed as demonstrating transsynaptic degeneration across the lateral geniculate nucleus to the anterior visual pathway. However, neuroimaging studies revealed abnormal deep venous drainage remote from the AVM nidus that directly involved the lateral geniculate nucleus and posterior optic tract.