Faculty Bibliography

AIM: Pain is a common feature of microvascular ischaemic ocular motor cranial nerve palsies (MP). The natural history of pain in this condition has not been studied. The purpose of this report is to define the spectrum of pain in isolated MP, with special reference to diabetic versus non-diabetic patients. Design and methods: Retrospective and prospective chart review was performed on 87 patients with acute-onset MP of a single cranial nerve (CN III, oculomotor; CN IV, trochlear; CN VI, abducens) that progressively improved or resolved over 6 months. RESULTS: Five of the 87 patients had two events, making the total number events 92. There were 39 (42.4%) CN III palsies, five (5.4%) CN IV palsies and 48 (52.2%) CN VI palsies. Thirty-six (41%) patients had diabetes. Pain was present in 57 (62%) events. The majority of diabetic and non-diabetic patients had pain. Pain preceded diplopia by 5.8 (SD 5.5) days in one-third of events. There was a trend towards greater pain with CN III palsies, but this was not statistically significant. Patients who experienced severe pain tended to have pain for a longer duration (26.4 (SD 21.7) days compared with 10.8 (SD 8.3) and 9.5 (SD 9) days for mild and moderate pain, respectively). There was no correlation between having diabetes and experiencing pain. CONCLUSIONS: The majority of MP are painful, regardless of the presence or absence of diabetes. Pain may occur prior to or concurrent with the onset of diplopia. Non-diabetic and diabetic patients presented with similar pain characteristics, contrary to the belief that diabetic patients have more pain associated with MP.

BACKGROUND: Contrast acuity (identification of low-contrast letters on a white background) is frequently reduced in patients with demyelinating optic neuropathy associated with multiple sclerosis (MS), even when high-contrast (Snellen) visual acuity is normal. Since visual evoked potentials (VEPs) induced with high-contrast pattern-reversal stimuli are typically increased in latency in demyelinating optic neuropathy, we asked if VEPs induced with low-contrast stimuli would be more prolonged and thus helpful in identifying demyelinating optic neuropathy in MS. METHODS: We studied 15 patients with clinically definite MS and 15 age-matched normal controls. All subjects underwent a neuro-ophthalmologic assessment, including measurement of high-contrast visual acuity and low-contrast acuities with 25%, 10%, 5%, 2.5%, and 1.25% contrast Sloan charts. In patients with MS, peripapillary retinal nerve fiber layer (RNFL) thickness was determined using optical coherence tomography. Monocular VEPs were induced using pattern-reversal checkerboard stimuli with 100% and 10% contrast between checks, at 5 spatial frequencies (8-130 minutes of arc). RESULTS: VEP latencies were significantly increased in response to low- compared with high-contrast stimuli in both groups. VEP latencies were significantly greater in patients with MS than controls for both high- and low-contrast stimuli. VEP latencies correlated with high- and low-contrast visual acuities and RNFL thickness. VEPs were less likely to be induced with low- than with high-contrast stimuli in eyes with severe residual visual loss. CONCLUSIONS: Visual evoked potentials obtained in patients with multiple sclerosis using low-contrast stimuli are increased in latency or absent when compared with those obtained using high-contrast stimuli and, thus, may prove to be helpful in identifying demyelinating optic neuropathy.

A patient with a traumatic optic tract hemorrhage is presented and discussed in the context of the literature on traumatic homonymous hemianopia. Radiographic demonstration of the injury on an MRI that was initially interpreted as normal emphasizes the difficulty of identification of small traumatic injuries and the importance of radiographic review in the context of clinical localization.

In late-onset Tay-Sachs disease (LOTS), saccades are interrupted by one or more transient decelerations. Some saccades reaccelerate and continue on before eye velocity reaches zero, even in darkness. Intervals between successive decelerations are not regularly spaced. Peak decelerations of horizontal and vertical components of oblique saccades in LOTS is more synchronous than those in control subjects. We hypothesize that these decelerations are caused by dysregulation of the fastigial nuclei (FN) of the cerebellum, which fire brain stem inhibitory burst neurons (IBNs).

Saccades normally place the eye on target with one smooth movement. In late-onset Tay-Sachs (LOTS), intrasaccadic transient decelerations occur that may result from (1) premature omnipause neuron (OPN) re-activation due to malfunction of the latch circuit that inhibits OPNs for the duration of the saccade or (2) premature inhibitory burst neuron (IBN) activation due to fastigial nucleus (FN) dysregulation by the dorsal cerebellar vermis. Neuroanatomic analysis of a LOTS brain was performed. Purkinje cells were absent and gliosis of the granular cell layer was present in the dorsal cerebellar vermis. Deep cerebellar nuclei contained large inclusions. IBNs were present with small inclusions. The sample did not contain the complete OPN region; however, neurons in the OPN region contained massive inclusions. Pathologic findings suggest that premature OPN re-activation and/or inappropriate firing of IBNs may be responsible for interrupted saccades in LOTS. Cerebellar clinical dysfunction, lack of saccadic slowing, and significant loss of cerebellar cells suggest that the second cause is more likely.

Proper evaluation and treatment of acquired nystagmus requires accurate characterization of nystagmus type and visual effects. This review addresses important historical and examination features of nystagmus and current concepts of pathogenesis and treatment of gaze-evoked nystagmus, nystagmus due to vision loss, acquired pendular nystagmus, peripheral and central vestibular nystagmus, and periodic alternating nystagmus.

The Miller Fisher syndrome (MFS) is a variant of Guillain-Barre syndrome with the clinical triad of areflexia, ataxia, and ophthalmoparesis. The classic pathologic mechanism of disease is considered to be peripheral nerve demyelination. We present a patient with binocular diplopia and a diagnosis of myasthenia gravis from 15 years prior. Electrophysiologic studies revealed a decremental response on repetitive nerve stimulation, suggesting recurrent myasthenia. However, pupillary light-near dissociation and areflexia were present and positive anti-GQ1b antibodies confirmed MFS. This patient highlights a developing recognition of impaired neuromuscular transmission in MFS. His presentation is discussed in the context of the animal and human literature on neuromuscular junction abnormalities in MFS.

Ocular misalignment and ophthalmoparesis result in the symptom of binocular diplopia. In the evaluation of diplopia, localization of the ocular motility disorder is the main objective. This requires a systematic approach and knowledge of the ocular motor pathways and actions of the extraocular muscles. This article reviews the components of the ocular motor pathway and presents helpful tools for localization and common sources of error in the assessment of ophthalmoparesis.