The influence of adaptation on visual motion detection in chronic sixth nerve palsy after treatment with botulinum toxin.

PURPOSE: To investigate changes in visual motion perception after treatment with botulinum toxin in patients with unilateral chronic lateral rectus muscle palsy. METHODS: Five patients and control subjects were asked to report the perceived drift direction of a sinusoidal grating that was initially stationary and then began to accelerate at 0.09 degrees /sec2 in a horizontal direction. The grating had a field size of 18.5 degrees and was presented monocularly with a contrast just above threshold for visibility for central vision. Both the paretic and non-affected eyes were tested. Psychophysical testing was performed under the following conditions: 1) before treatment and testing, patients occluded their paretic eye for at least three days to avoid diplopia. 2) After treatment with botulinum toxin, alignment was corrected and patients stopped occluding their paretic eye for at least three days before testing. The control subjects occluded their non-dominant eye for three days before testing. RESULTS: In condition 1, no differences in motion detection values between patients and control subjects were found. In condition 2, motion detection thresholds were raised approximately 0.15 degrees /sec as compared to pre-treatment values and compared to the control group. CONCLUSIONS: After treatment, a raised threshold for motion detection is one mechanism used to avoid oscillopsia and visuo-vestibular disorientation during head movements in patients with chronic paralytic squint. This study lends evidence that perceptual-adaptive, compensatory mechanisms develop to reduce oscillopsia and disorientation rather than being caused by abnormal cortical motion processing or defective eye muscle action.

Time-varying, slow-phase component interaction in congenital nystagmus.

We investigated the nystagmus of a 12-year-old boy with suspected X-linked congenital nystagmus (CN) and exophoria to determine the underlying mechanisms and component signals in the 'dual-velocity' and other slow phases of his Asymmetric (a)Periodic Alternating Nystagmus (APAN). Fast Fourier transforms (FFT) were performed on the waveforms and residual data after subtracting a sawtooth waveform whose amplitude and frequency matched those of the jerk nystagmus. The FFT analyses identified two frequency components (jerk--4 Hz and pendular--4 and 8 Hz, variable) that varied differently in intensity and frequency/phase over the time-course of the APAN. We synthesized each of the patient's slow phases using summation of sawtooth and sinusoidal waveforms. The resulting waveforms included jerk (with different slow-phase appearances), dual jerk, and pendular. We demonstrated that the pendular nystagmus seen during the neutral phase of APAN and the appearance of either decelerating (mimicking latent nystagmus), dual-velocity, or dual-jerk slow phases can be explained and produced by the summation of linear and pendular components of variable amplitudes and frequencies/phases. Thus, one mechanism may be responsible for all the variation seen in this patient's slow phases, rather than the less parsimonious hypothesis of a switched-tonic-imbalance mechanism that we had originally suggested to simulate the dual-velocity waveform.

Vestibular perception in patients with acquired ophthalmoplegia.

Using a perceptual technique it is shown that patients with chronic external ophthalmoplegia have shortened vestibular responses. It is postulated that this is secondary to the retinal image slip experienced by these patients during head movements and a useful compensatory mechanism to suppress motion-induced sickness and spatial disorientation.

The pupil in dominant optic atrophy.

PURPOSE: To compare visual and pupil afferent function in dominant optic atrophy (DOA). METHODS: Patients with DOA who belonged to families showing evidence of linkage to the locus on chromosome 3q28-qter were recruited from the Moorfields Genetic Register. Patients and healthy control subjects underwent visual and pupil perimetry using a modified automated perimeter (Octopus 1-2-3; Interzeag, Schlieren, Switzerland). Five stimulus locations were tested: fixation, and at 17 degrees eccentricity along the 45 degrees and 135 degrees meridians in all four quadrants. The visual deficit (difference in decibels between the patient's luminance threshold and that in age-matched healthy control subjects) was compared directly with the pupil deficit (difference in decibels between the stimulus intensity giving the patient's pupil response and that giving an equivalent pupil response in healthy control subjects) at each test location. RESULTS: Visual deficits and pupil afferent deficits were found at all five locations. The visual deficits were significantly greater than the pupil deficits at the four peripheral locations (median difference = 6.3 dB, P: < 0.001). At fixation, the difference was not significant (median difference = 2.3 dB, P: = 0.407). CONCLUSIONS: Pupil function appears less affected than visual function at four of five locations tested. This result provides evidence that the retinotectal fibers serving the pupil light reflex are less susceptible to damage from the OPA1 genetic defect than the retinogeniculate fibers serving vision.

Recognizing periodic alternating nystagmus.

Congenital or acquired periodic alternating nystagmus (PAN) is characterized by nystagmus occurring in a cycle. The cycle consists of a left-beating nystagmus, a transition phase, a right-beating nystagmus, and a further transition phase. The purpose of this review is to assist the clinician in the recognition of periodic alternating nystagmus (PAN), either as a type of congenital nystagmus or in its acquired form, and to highlight why such identification is important. Recent studies using eye movement recordings are reviewed to point out the frequency of congenital PAN in samples of patients with congenital nystagmus, and to describe the characteristics of the waveforms and the influence of foveation time on the alternation of head turns. Classical and new surgical alternatives are reported. The identification of congenital PAN is essential when surgical treatment is being considered for the correction of anomalous head postures. Acquired PAN is usually due to cerebellar disease and causes oscillopsia. Unlike other forms of acquired nystagmus, it responds well to drug treatment.

Visual control of postural orientation and equilibrium in congenital nystagmus.

PURPOSE: To investigate how humans with congenital nystagmus (CN) use visual information to stabilize and orient their bodies in space. METHODS: Center of foot pressure (COP) and head displacements in the lateral plane were recorded using a sway platform and Schottky barrier photodetector, respectively. In experiment 1, a comparison was made of the oscillatory characteristics of body sway with eyes open compared with eyes closed. Experiment 2 studied the postural readjustments made in response to absolute or relative motion (motion parallax) of objects in the visual scene, generated by lateral displacement of background scenery. RESULTS: Experiment 1 revealed that subjects with CN were not able to use visual information to stabilize COP but were able to stabilize the head at frequencies lower than 1 Hz. Experiment 2 showed that in response to the displacement of a visual display, for both absolute motion and motion parallax, subjects with CN reoriented their body in space in a manner similar to control subjects. CONCLUSIONS: The results suggest that despite involuntary eye movements, subjects with CN use orientation cues to control their posture, but not dynamic cues useful to control the rapid oscillations that are particularly important at the level of COP. These findings suggest that in CN, visual control of posture is restricted by low-frequency sampling of the visual scene.

The presumed influence of attention on accuracy in the developmental eye movement (DEM) test.

BACKGROUND: The developmental eye movement (DEM) test is a clinical test used widely to evaluate ocular motility function (accuracy and speed) in school-age children. PURPOSE: The purpose of this study was to investigate, retrospectively, the change in accuracy over time while performing the DEM horizontal reading task in children. METHODS: The charts from children who had performed the DEM test during a routine eye examination in a pediatric optometry service were reviewed. The study included 22 patients (6 to 11 years old, 12 boys, 10 girls) who had a routine eye examination that was precepted by one of the authors (R.C.) during the period of 1995 to 1999. Patients were divided into two categories: 1) those with abnormal DEM test results and 2) a control group consisting of those with normal DEM test results. Chart review was done consecutively within each category. Collected data included patient age, gender, refractive error, and DEM test results. For analysis, the horizontal task of the DEM was divided into two halves (I and II), Part I always preceded part II, and data was sorted as the number of errors per part. RESULTS: More errors in accuracy occurred in part II than in part I (Wilcoxon signed rank test, p < or = 0.01) of the horizontal DEM test in the group of subjects with an abnormal DEM test. No differences in the number of errors in parts I and II of the horizontal task of the DEM were found in the control group. CONCLUSIONS: Findings showed that when excessive errors in accuracy occurred, the number of errors increased over time. If the errors were caused by an oculomotor dysfunction found in the DEM, errors should be equally distributed throughout the text. If errors were caused by fatigue, a difference in parts I and II should have occurred in both the test and the control group. These findings suggest that attention may influence accuracy over time in those patients that do poorly on the DEM test.

Comparing pupil function with visual function in patients with Leber's hereditary optic neuropathy.

PURPOSE: To compare pupil function with visual function in patients with Leber's hereditary optic neuropathy (LHON) and age-matched normal control subjects. METHODS: Visual function was assessed by measuring the perceptual thresholds at five central locations in the visual field using automated static perimetry. Pupil function was assessed by recording the pupil responses to a standard intensity light stimulus (size equivalent to a Goldmann V target) presented at the same five locations in the visual field. The extent of the pupil afferent defect in LHON patients was quantified by establishing the relationship between stimulus intensity and the size of the pupil response in normal subjects and then interpolating the equivalent luminance deficit in LHON patients from the size of their pupil responses. RESULTS: At all five locations tested, the pupil responses were significantly reduced in amplitude, and the perceptual thresholds were significantly raised in LHON patients compared with normal control subjects. A nonparametric analysis of perceptual and pupil responses to perithreshold stimuli showed that a stimulus that was not perceived was three times more likely to be followed by a pupil response in a LHON patient than in a normal subject (P < 0.001). A quantitative comparison showed that the visual deficits exceeded the pupil deficits by on average 7.5 dB at all tested locations. CONCLUSIONS: Although both visual and pupil function are abnormal in LHON, there appears to be relative sparing of the pupil afferent fibers.

The incidence and waveform characteristics of periodic alternating nystagmus in congenital nystagmus.

PURPOSE: To investigate the incidence and waveform characteristics of periodic alternating nystagmus, (PAN) in congenital nystagmus (CN). METHODS: In a prospective study, 18 patients with CN without associated sensory defects agreed to undergo eye movement documentation using binocular infrared oculography. Two of the 18 had a diagnosis of suspected PAN before entering the study. The patients sat in a dimly lit room and viewed an LED (4 min in diameter) located in the primary position, at a distance of 100 cm. During an 8-minute recording, patients were read a story of neutral interest to hold attention at a constant level. PAN was defined as a left-beating nystagmus, a transition phase, a right-beating nystagmus, and a final transition phase; the sequence was then repeated. RESULTS: Seven of the 18 patients had PAN (median cycle: 223 seconds, range 180-307 seconds). The periodicity of the cycles for each adult patient was regular, although the phases within a cycle were often asymmetric. Six of the seven patients had an anomalous head posture (AHP), and in five the AHP was in only one direction. Except for one patient, the PAN waveforms had an increasing slow-phase velocity in at least one phase of the cycle; in the other phase they were linear. CONCLUSIONS: The occurrence of PAN in CN is not as rare as previously thought and can be missed because of the long cycles and the use of only one AHP. The AHP was dependent on, and could be predicted from, the waveforms containing the longest foveation times. Although the waveforms and foveation times may differ among the phases of the PAN cycle, the periodicity of the cycle was usually regular and therefore predictable. Identification of PAN is essential in cases in which surgical treatment is considered for correction of AHPs.

Vestibular perception of angular velocity in normal subjects and in patients with congenital nystagmus.

A technique is described for the assessment of vestibular sensation. The two main goals of the study were (i) to compare the perception of angular velocity with the eye velocity output of the vestibulo-ocular reflex and (ii) to study vestibular function in patients with congenital nystagmus; this was needed since most previous studies, based on eye movement recordings, have been inconclusive. Subjects indicated their perceived angular velocity by turning by hand a wheel connected to a tachometer. The vestibular stimuli used consisted of sudden deceleration from rotation at a constant horizontal velocity of 90 degrees /s ('stopping' responses). Eye movements were recorded simultaneously with electro-oculography. In normal subjects the perceived angular velocity decayed from the moment of deceleration in an exponential fashion. The mean time constant of sensation decay was approximately 16 s. Eye movement velocity decayed with a similar exponential trajectory (time constant 16 s). Congenital nystagmus patients showed markedly shortened vestibular sensation (mean time constant 7 s). The following conclusions can be drawn: (i) the similarity of the eye velocity and perceptual responses suggests that these two systems receive a vestibular signal which has been similarly processed; (ii) the time constant of the responses indicates that this vestibular signal probably originates in the same brainstem 'velocity storage' integrator; (iii) the technique described is useful for clinical assessment of vestibular function, particularly in patients with ocular motility disorders; (iv) patients with congenital nystagmus have short vestibular time constants, which is probably due to changes induced in velocity storage processing by the persistent retinal image motion present in these patients.

Dissociated effects of botulinum toxin chemodenervation on ocular deviation and saccade dynamics in chronic lateral rectus palsy.

AIM: Changes in saccade velocity/amplitude characteristics (main sequence) and attenuation of distance esotropia in response to botulinum toxin (BTX-A) chemodenervation of the antagonist medial rectus were studied in a group of nine patients with chronic lateral rectus palsy. METHODS: Serial measurements of ocular deviation and infrared oculograms of saccadic eye movements to targets at 5 degrees-20 degrees of lateral gaze were made before injection and at 2, 4, 8, 16, and 20 weeks after injection. RESULTS: At 2 weeks after injection, the ocular deviation changed by a mean of 34.5 prism dioptres and the 5 degrees and 10 degrees adduction saccades were significantly slowed (p < 0.02 Wilcoxon signed rank test). By the second examination, however, the adducting saccade peak velocity had returned to normal while the mean ocular deviation remained significantly changed (p = 0.01 Wilcoxon matched pairs). By 20 weeks the mean ocular deviation was not significantly different from that before injection (p = 0.14 matched pairs). CONCLUSIONS: The ocular realignment caused by BTX-A may persist after saccadic function has been restored. This may be because toxin may have a more profound and long lasting effect on the orbital singly innervated fibres which are active tonically at rest to hold gaze whereas there is relative sparing of the additional motor units recruited during fast eye movements.

Reduced duration of a visual motion aftereffect in congenital nystagmus.

Congenital nystagmus (CN) is a primarily horizontal, involuntary, conjugate eye movement which can be observed soon after birth or during the first half-year of life. Individuals with CN rarely complain of oscillopsia. Using a motion aftereffect (MAE), we investigated if individuals with CN have abnormalities in motion perception and if any such abnormality could be due to nystagmus or to compensatory mechanisms to avoid oscillopsia. In task A, patients (n=10) and control subjects (n=10) indicated the direction, duration and relative velocity of MAEs. The subjects binocularly viewed a high contrast, grey scale grating (0.23 cyc/deg; visual angle: 18.3 deg) moving upward or downward at 1, 3, and 6 deg/sec for 60 sec. Vertical optokinetic nystagmus (OKN) was monitored. In task B, patients (n=8) and control subjects (n=8) viewed similar spatial frequency gratings (visual angle: 40.7 degs; 0.5, 0.2, 0.08 cyc/deg) which moved at 4, 10, and 16 deg/sec for 60 sec. In task C, five control subjects, with induced vestibular nystagmus, viewed a grating (0.2 cyc/deg; visual acuity: 28.5 deg), moving upward for 40 sec. In all three tasks, after adaptation with the moving grating, subjects viewed the then static grating and reported the duration and direction of the MAE. One CN patient and eight control subjects reported MABs at all three test velocities in task A. When patients exhibited OKN, the gain was close to one, as in the control group. In task B, seven of the eight patients and all of the control subjects had MABs at the faster adaptation velocities. CN patients had less MAEs at an adaptation velocity of 4 deg/sec and when MAEs were observed, the duration of the illusory motion was reduced by approximately 48%. Control subjects, with induced vestibular nystagmus, reported MAEs at 4 deg/sec (task C). These findings indicate that nystagmus cannot be the only factor accounting for the suppression of motion perception and suggest that compensatory mechanisms used to avoid oscillopsia contribute to the differences found between the groups.

Motion detection deficits in infantile esotropia without nystagmus.

PURPOSE: To investigate whether adults with infantile strabismus but without latent nystagmus have abnormalities of horizontal motion detection. METHODS: Eleven adult subjects with infantile esotropia but without latent nystagmus and 15 control subjects were required to detect the onset of motion and drift direction of a sinusoidal, spatial frequency grating that moved with linearly increasing velocity. The grating was presented monocularly in paracentral vision at an eccentricity of 16.5 degrees with a field size of 18 degrees. The contrast of the grating was just above contrast threshold for visibility. RESULTS: The mean velocity threshold for detection of motion was raised significantly in the patient group compared with the control group. Nine of the 11 subjects with infantile esotropia demonstrated directional asymmetry for the detection of motion. Thresholds were elevated more often when the grating was moving nasally in the squinting eye and temporally in the nonsquinting eye, and raised thresholds were more prevalent in the squinting eye. CONCLUSIONS: The findings indicate that in infantile esotropia, the presence of motion perception deficits are not always associated with the development of latent nystagmus. The predominance of nasally directed motion deficits in the squinting eye and temporally directed motion deficits in the nonsquinting eye was unexpected and may have been caused by abnormal development of cortical motion processing.

Visually and memory guided saccades in a case of cerebellar saccadic dysmetria.

Saccades under four specific test conditions (visually guided, visually remembered, vestibular remembered, and cervical remembered) were studied in a 38 year old man with ocular dysmetria due to an angioma of the dorsal cerebellar vermis. The aim of the study was to investigate if the saccadic disorder was specific to certain subsets of saccades elicited by different sensory modalities. The experiments showed that initial saccades were equally hypermetric in all four conditions and that final eye position was normal in all memory guided saccade tests. Eye movements differed after the initial saccade, however. Whereas corrective saccades were seen in most visually guided and visually remembered experiments, postsaccadic centripetal drifts were documented in non-visual (vestibular and cervical) remembered saccades. These results indicate that the cerebellar vermis modulates the amplitude of the initial saccade (pulse size of saccadic innervation) independently of the saccadic task. The finding that post-saccadic drift never occurred when saccades were programmed using visual positional information suggests that the dorsal vermis may participate in the process of pulse step integration of saccades elicited by memorised vestibulo-cervical information.

Visual evoked response asymmetry only in the albino member of a family with congenital nystagmus.

PURPOSE: To examine the purported relationship between visual fiber misrouting and congenital nystagmus (CN) by studying a family containing members with either hereditary CN alone or in conjunction with albinism. METHODS: Eight relatives in three generations of a family with two genetic disorders (congenital nystagmus [CN] and albinism) underwent complete ophthalmologic examination and visual evoked potential (VEP) assessment of visual pathway organization using a luminance flash and checkerboard pattern onset/offset stimulus paradigm. Age-matched controls patients (albino, CN, or normal) corresponding to the three affected family members underwent the same procedure. RESULTS: The standard VEP albino misrouting test did not reveal any signs of abnormality in all family members tested except for the clinically diagnosed 8-month-old albino proband patient. Visual evoked potential assessment from the albino patient evinced contralateral asymmetry characteristic of aberrant temporal retinostriate projections. CONCLUSIONS: Although CN and albinism share some of the same clinical symptoms, these findings indicate that the disorders may be inherited and manifested independently in members of one family. Furthermore, the functional and/or structural factors responsible for CN cannot be readily ascribed to VEP retinal-cortical misprojections recorded in albinism.

VEP projections in congenital nystagmus; VEP asymmetry in albinism: a comparison study.

Visual evoked potential (VEP) asymmetry in which a preponderance of nasal and temporal retina afferents project to the contralateral hemisphere after full-field monocular stimulation is considered specific to albinism. Some reports, however, suggest that patients with congenital nystagmus (CN) share the albino-like visual pathway anomaly. To examine the clinical specificity of albino misrouting, VEP topography was assessed in ten patients with congenital nystagmus and in ten age-matched albino patients. As an additional control, the VEP response profiles from eight albino patients with no nystagmus were also evaluated. The results are definitive; VEP contralateral asymmetry reflecting temporal retinal misprojection is evinced only in albino patients. Furthermore, ocular-motor instabilities in CN cannot be readily attributed to albino-type misrouted retinal-cortical projections.

[Physiologic and pathologic rebound nystagmus. Description and comparison]. / Physiologischer und pathologischer Rebound-Nystagmus. Beschreibung und Vergleich.

Using a binocular, infrared charged coupled device (CCD), an eye tracker coupled with an Olivetti M24 PC (resolution up to 0.1 degrees, scanning with 80 frames/s), the eye movements of 20 normal individuals with normal visual acuity and binocular function were recorded to detect physiological endpoint (EPN) and rebound nystagmus (RN). Each subject was asked to fixate a target located in the primary position (PP) and after 5 s of recording time, to look at a target either 50 degrees to the right or left of the PP for approximately 20 s and then return for the last few seconds to the PP, EPN recordings were made with the room lights on and RN recordings were made both with the lights on and in total darkness. A forehead and chin rest with bite board were used. Twelve of the 20 subjects showed EPN and RN with the lights on. The 8 subjects that did not demonstrate EPN also showed no RN with the lights on. Recordings from all 20 subjects showed RN in darkness. No differences in amplitude were found between the abducted and adducted eyes. Although clear differences in the characteristics of gaze paretic or drug-related lateral gaze nystagmus and EPN have been found, no systematic differences in RN under lighted conditions had been observed between patients and normal subjects.

[Subclinical eye movements as an indicator for inheritance of congenital nystagmus and central nervous system disease]. / Subklinische Augenbewegungen als Indikator für den Verebungsgang bei kongenitalem Nystagmus und zentralnervöser Erkrankung.

Clinically unaffected relatives of families with a history of either inherited congenital nystagmus or inherited neurogenic muscular and cerebellar atrophy underwent electrooculographic examination under three distinct test conditions. We found an increase in the number of square wave jerks, a higher than normal intensity score (defined in terms of frequency X amplitude of an involuntary saccade, unit: o/s) and nystagmus as compared with 110 normal individuals ranging in age from 21 to 89 years. These findings suggest a possible autosomal dominant mode of inheritance in the case study of congenital nystagmus presented. The results show abnormal eye movements in some family members from a family with inherited cerebellar degeneration with acquired nystagmus, suggesting that these family members are affected with the disorder. This study documents the rarely described observation of a connection between inherited cerebellar degeneration with inherited distal neurogenic muscular atrophy.

Normal square wave jerks in differing age groups.

This report details the characteristics of normal square wave jerks (SWJ) over a broad age range. Sixty normally sighted subjects, categorized into three age groups (35-49 yr, 50-64 yr, and 65-89 yr) underwent electrooculographic (EOG) examination to investigate the characteristics of normal SWJ. The frequency, duration, and amplitude of SWJ per minute were calculated in three clinically used test conditions: 1) with a fixation point in a lighted room; 2) with eyes closed and 3) in darkness without a fixation point. Results were compared over age and conditions as well as with the scores of 50 normal young subjects (20-37 yr). SWJ were recorded in all conditions, with the highest number found with closed eyes and in darkness for all age groups. Contrary to earlier findings, no statistical differences in frequency of SWJ per minute due to age were observed. These findings describe a range of normalcy for these three EOG conditions from which pathology can be inferred.