Reprinted from the Archives of Ophthalmology

• Manifest latent nystagmus (MLN) wa

Biologically Relevant Models of Infantile Nystagmus Syndrome: The Requirement for Behavioral Ocular Motor System Models

ABSTRACT Infantile nystagmus syndrome (I NS) is a combination of several types of nystagmus, each representing dysfunction in one subsystem of the oc ular motor system (OMS) and having characteristic waveforms. Eye-movement recordings are the only certain way to identifY IN and differentiate it from other types. The waveform classification scheme in use for 30 years is both accurate, inclusive, and suggests the underlying subsystem instabilities. In dif ferent individuals, they may appear at birth (hard wired) or in early infancy (developmental). The primary subsystem instability in IN is hypothesized to lie in the normally underdamped smooth pursuit system; vestibular dysfunction (imbalance) may also be present. Less often, the nucleus of the optic tract may be involved. Ocular motility studies over the past 40 years have demonstrated that saccades and gaze holding are normal in the INS and saccades contained within IN waveforms are always corrective; i.e., they cannot be the initiating movement responsible for IN. Because there are an infinite number of solu tions to simulating specific waveforms, models that merely generate waveforms that resemble IN in isolation are of little use, either clinically or to increase our understanding of the underlying mechanisms of IN. A biologically relevant model of the INS should be part of, and operate within, a complete OMS model, capable of reproducing the normal ocular motor behavior of these in dividuals while still oscillating; i.e., the model, like the patient, must not have oscillopsia and be able to respond correctly to various target inputs

Edrophonium test in Eaton-Lambert syndrome: Quantitative oculography

Article abstract-Accurate ocular motility recordings were made of the saccadic responses of five patients with Eaton Lambert syndrome (ELS). It was found that, contrary to common belief, the ocular motor system is affected. The sacca des of ELS patients mimicked those of patients with myasthenia gravis (MG). Both groups exhibited hypometria and multiple, closely spaced saccades. Two patients demonstrated both saccadic facilitation and positive edrophonium tests. The ELS patients had slow or normal saccadic velocities, not the "super-fast" velocities found in patients with ocular MG. NEUROLOGY (Cleveland) 1983;33:1157-63 Edrophonium test in Eaton-Lambert syndrome: Quantitative oculography The Eaton-Lambert syndrome (ELS)1 is attributed to impaired release of acetylcholine from nerve ter minals.2 Unlike myasthenia gravis (M G), the weak ness primarily involves proximal limb muscles, sparing cranial muscles.2•3 The response to edrophonium is slight or absent in most cases, but occasionally positive.4 Also, ELS shows facilitation both electronically and clinically, 5.6 in contrast to the decremental response of MG. We have reported oculographic studies of saccadic eye movements and the response to edrophonium in ocular myasthenia.7•8 Many of the abnormalities seemed due to increases in central ocular motor gain in com pensation for the peripheral defect. We now report quantitative oculographic studies of saccadic eye movements and the effect of edrophonium in five patients with ELS. None of the patients had obvious eye movement abnormalities when examined clinically by neuro-ophthalmolo gists. The study was prompted, in part, by reports of subclinical eye movement abnormalities uncovered by oculography in MS,9 amyotrophic lateral scle rosis,1O and Alzheimer's disease,u Case reports. Patient 1. For 6 months, this 66-year-old woman noted progressive weakness of all four limbs, dys phagia, and dry mouth, but no ptosis, diplopia, or dys arthria. The diagnosis of MG had been made by a neurologist after a "positive edrophonium test." She was treated with pyridostigmine (120 mg, four times a day for 8 weeks) without benefit. Examination was normal except for proximal limb weakness. Few brief contractions of the proximal muscles appeared to result in transient improvement of strength. Tendon reflexes were absent. Intravenous administration of 10 milligrams of edrophonium did not improve muscle strength. AChR antibodies were not detected in serum by radio immunoassay. Neuromuscular transmission studies revealed markedly decreased amplitude of the compound muscle action poten tial (CMAP) of the abductor pollicis brevis (0.4 m V). After 10 seconds of maximal contraction, there was an increment ofl,OOO% in the amplitude of the CMAP. Two-per-second stimulation showed a decremental response of 25% in the same muscle. Similar findings were noted in other muscles. Nerve conduction studies were normal. On electromyogra phy, there was moment-to-moment variation in the ampli tude of the motor unit potentials, but the amplitudes and durations were normal. Roentgenogram of the chest revealed a large hilar and paratracheal mass on the right side. Biopsy of the lymph nodes during mediastinotomy revealed metastatic oat cell carcinoma. She was given guanidine hydrochloride, 15 mg/ kg body weight/day. Dysphagia, proximal muscle strength, and the neuromuscular transmission studies improved. She was started on chemotherapy and discharged on guanidine, with no side effects, and maintained improve ment. Patient 2. A 55-year-old man noted muscle soreness and weakness. He could walk only a few paces with difficulty. He had occasional transient diplopia for about 3 months before evaluation, but no cranial symptoms other than dry mouth. On examination, he could not rise from a bed or

Effect of Gait Imagery Tasks on Lower Limb Muscle Activity With Respect to Body Posture

The objective of this study was to evaluate the effect of gait imagery tasks on lowerlimb muscle activity with respect to body posture. The sitting and standing position and lower limb muscle activity were evaluated in 27 healthy female students (24.4±1.3 years, 167.2±5.2 cm, 60.10±6.4 kg). Surface electromyography was assessed during rest and in three different experimental conditions using mental imagery. These included a rhythmic gait, rhythmic gait simultaneously with observation of a model, and rhythmic gait after performing rhythmic gait. The normalized root mean square EMG values with respect to corresponding rest position were compared using non-parametric statistics. Standing gait imagery tasks had facilitatory effect on proximal lower limb muscle activity. However, electromyography activity of distal leg muscles decreased for all gait imagery tasks in the sitting position, when the proprioceptive feedback was less appropriate. For subsequent gait motor imagery tasks, the muscle activity decreased, probably as result of habituation. In conclusion, the effect of motor imagery on muscle activity appears to depend on relative strength of facilitatory and inhibitory inputs