Eye movements, visual acuity and spatial constancy

Abstract How are eye movements related to acuity or to the lack of spatial constancy, oscillopsia (aSap) ? How do subjects with congenital nystagmus (CN) suppress aSap? Can we apply their strategies to cases of acquired nystagmus? In normals, the maintenance of target foveation with low retinal slip is thought to be necessary for good visual acuity. Retinal slip velocities below 1.67-4 degjsec have been given as upper bounds for good vision. Subjects with CN do not usually have asap and can have good (even normal) visual acuity. CN subjects can maintain target position (SD = 0.21 deg) and low retinal slip velocities (SD = 1.97 degj sec). Previously, we identified two possible mechanisms for the suppression of asap in subjects with CN: 1) efference copy of the CN waveform to negate the effects of the oscillation or 2) the stable vision available during foveation periods. A 48 year-old man with hereditary CN lost consciousness; when he came to, he had troublesome, intermittent aSap. Recordings revealed a jerk left with extended foveation (JLej) waveform when asap was absent (SD of eye position was 0.24 deg and SD of retinal slip velocity was 1.87 degj sec). However, with the onset of asap, his CN waveform abruptly changed to jerk right (JR) and was biased several degrees to the right of the target. Phase-plane analysis revealed that, during the periods of asap, the JR waveform did not enter the foveation window defined by the limits, 0 ± 0.5 deg and 0 ± 4. 0 degj sec. CN direction shifts, common in some CN subjects, do not normally result in loss of foveation periods or aSap. During electronic retinal image stabilization (RIS) transient asap persisted with the same CN waveform changes. RIS usually results in asap that can be suppressed by the CN subject. This subject also suppressed asap during his normal JLef waveform but was unable to do so when the biased, JR waveform appeared. The efference-copy mechanism is tenable only if the man s pathology occurred at a point beyond where the efference-copy signal is fed back 106 L. F. DELL'OSSO Stable vision by itself is insuffi cient since RIS causes asap in eN. We conclude that the mechanism that prevents asap requires the motor stability provided by the eN foveation periods. Without them, asap is not suppressed even during RIS. If we presume that eN subjects make use of existing mechanisms for preserving the sense of spatial constancy (even allowing that they may have optimized these mechanisms), the suppression of asap in cases of acquired nystagmus should be possible if we can provide a foveation window during each nystagmus cycle

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

The Nystagmus Blockage Syndrome Congenital Nystagmus, Manifest Latent Nystagmus, or Doth?

We have carefully studied, by quantitative oculography, a patient with the nystagmus blockage syndrome (NBS), and two patients with a similar disorder of eye movements that might be mistaken clinically for NBS. Our recordings revealed two distinctly different abnormalities present in a single patient with NBS. Our NBS patient exhibited congenital nystagmus (CN) waveforms when viewing at distance; the CN did not damp with convergence on a near target. When the patient allowed one eye to become esotropic, however, the nystagmus damped considerably and abruptly changed from CN to manifest latent nystagmus (MLN). This peculiar transition from CN to MLN has not been described previously. The appearance of MLN in a case with ongoing CN suggests that two different mechanisms may underlie NBS, since the only other case documented with eye movement recordings showed no transition to MLN. Because the diagnosis of NBS usually is made on evidence of clinical signs alone, it is probable that these two types have been combined indiscriminately and presented as one syndrome. In addition, our discovery of two mechanisms discernable only by quantitative recording suggests that NBS has been diagnosed inappropriately in patients with clinically similar but oculographically different eye signs. Further quantitative studies are required to fully define NBS and to determine if these are the only two mechanisms found in this syndrome. Invest Ophthalmol Vis Sci 24:1580-1587, 198

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

The National Aeronautics and Space Administration interdisciplinary studies in space technology at the University of Kansas

A broad range of research projects contained in a cooperative space technology program at the University of Kansas are reported as they relate to the following three areas of interdisciplinary interest: (1) remote sensing of earth resources; (2) stability and control of light and general aviation aircraft; and (3) the vibrational response characteristics of aeronautical and space vehicles. Details of specific research efforts are given under their appropriate departments, among which are aerospace engineering, chemical and petroleum engineering, environmental health, water resources, the remote sensing laboratory, and geoscience applications studies

Evidence of Socio-Economic Classlessness in the Major Fiction of Daniel Defoe

This investigation will consider the thesis that the fiction of Daniel Defoe contains definite indications that he idealizes communism in the sense that he seems to uphold a system in which goods are owned in common and are available to all as needed. Previous criticism of the work of Defoe has considered the apparent dichotomy between his presentations of seemingly virtuous moralizing alongside mercenary capitalism. The critics of my acquaintance discuss these separately and are apparently unable to correlate Defoe’s morality with his economics, except, perhaps, as ironic device. Instead, this thesis will submit that Defoe’s moral and economic beliefs are at odds at all; rather they are growths of consistent thought based upon socio-economic classlessness. Chapter II will review the criticism pertinent to the topic under consideration. Chapter III will consider Defoe’s idea of economic classlessness in the Robinson Crusoe trilogy. Chapter IV will continue the analysis of Defoe’s theme of ideal economic classlessness by reference to Captain Singleton, Moll Flanders, Moxana, and A Journal of the Plague Year. All these narratives definitely indicate that Defoe’s model society is classless. In this thesis certain words often recur which seem to have special meanings to Defoe. In order that the reader may more easily understand this study, these words will be defined in this section as Defoe seemed to define them in his fiction. Quite the contrary, Defoe saw that England was moving further and further away from a communal state. Defoe, therefore, preached against capitalism by writing stories about people who are caught in a society which has capitalistic classes at its foundation. His narratives often portray such people as Moll Flanders and Colonel Jack who are forced to steal in order to live because capitalism provides no useful place for them in its society. By “middle class” then, Defoe apparently means that class of people in England who heve enough money to live contentedly and who do not strive for more than is necessary for maintenance of self and family. Lastly, in this study, the terms “Capitalism” and “communism” are void of most of their twentieth century connotations. In this theses, then, the two words, “communism” and “capitalism”, only represent an emphasis upon the community at one pole and upon the individual at the other

Aerospace Medicine and Biology. A continuing bibliography with indexes

This bibliography lists 286 reports, articles and other documents introduced into the NASA scientific and technical information system in March 1983

Studies in geophysics: The Earth's electrical environment

The Earth is electrified. Between the surface and the outer reaches of the atmosphere, there is a global circuit that is maintained by worldwide thunderstorm activity and by upper atmospheric dynamo processes. The highest voltages approach a billion volts and are generated within thunderclouds, where lightning is a visual display of the cloud's electrical nature. The largest currents in the circuit, approaching a million amperes, are associated with the aurora. Because there have been significant advances in understanding many of the component parts of the global electric circuit (lightning, cloud electrification, electrical processes in specific atmospheric regions, and telluric currents), a principal research challenge is to understand how these components interact to shape the global circuit. Increased basic understanding in this field has many potential practical applications, including lightning protection, the design of advanced aircraft and spacecraft, and improvements in weather prediction

Nystagmus, Saccadic Intrusions/Oscillations, and Oscillopsia

Understanding the pathophysiology of ocular oscillations necessitates differentia tion between those involving only the slow system and those that are purely sac cadic. Oscillations containing both saccades and slow phases require identification of both the causative phase (i. e. , that which takes the eyes away from their in tended direction) and the corrective phase. Modem recording methods have made possible these determinations and thereby clarified the underlying ocular motor mechanisms responsible for many oscillations. The definitions and categorizations used herein result from applying criteria de rived from accurate ocular motility recordings. They differentiate between nystag mus and saccadic oscillations, and as a result, I have found that some saccadic oscillations were originally described using the word nystagmus . Most oscillations were named before the benefits of accurate recordings. Quotation marks are use

T.: Square wave oscillation. The relationship of saccadic intrusions and oscillations. Neuro-ophthalmology (Amsterdam) 4

ABSTRACT. A patient with progressive supranuclear palsy exhibited an extremely high number of square wave jerks. These usually sporadic saccadic intrusions were so frequent as to form a continuous oscillation. Such a phenomenon suggests an underlying commonality between sporadic saccadic intrusions (square wave jerks, saccadic pulses and double saccadic pulses) and saccadic oscillations (macro square wave jerks, MSO and flutter)