Comparison of latent nystagmus and nasotemporal asymmetries of optokinetic nystagmus in adult humans and macaque monkeys who have infantile strabismus

To determine whether macaque monkeys with infantile strabismus have latent nystagmus and directional asymmetries of horizontal optokinetic nystagmus (OKN) similar to those of humans with infantile strabismus, the authors recorded eye movements under conditions of monocular viewing. The presence of latent fixation nystagmus was tested by requiring the subjects to steadily fixate a stationary target subtending less than I deg of visual arc. OKN was tested using high-contrast, vertically-oriented moving stripes that filled 80 deg of the visual field. A macaque monkey who had infantile strabismus induced by alternating occlusion from birth showed latent nystagmus highly similar to that recorded in an adult human subject with infantile strabismus. The strabismic monkey also had asymmetric OKN similar to that of the strabismic human, favoring nasally-directed stimulus motion when viewing with either eye. Neither nystagmus nor an OKN asymmetry was observed in a normal macaque or in humans who had normal binocular vision. The findings of latent nystagmus and OKN asymmetries in the strabismic monkey support the notion that monkeys who have infantile-onset strabismus are an appropriate ocular motor model of human infantile strabismus.     

Interrelations between measures of visual acuity and parameters of eye movement in congenital nystagmus

The authors assessed relationships between visual acuity and the amplitude, frequency, intensity, and duration of foveation periods in a retrospective study of 32 patients. Twenty-four patients had congenital idiopathic nystagmus, and eight patients had nystagmus and albinism. Visual acuity was determined for Landolt ring optotypes and, as the extrapolated high-frequency cutoff of the contrast sensitivity function, for horizontal and vertical gratings. No significant correlation existed between acuity and any measured eye movement parameter; however, optotype acuity was related to the magnitude of astigmatic refractive correction, both in patients with idiopathic nystagmus and in albinos. In a subgroup of patients with idiopathic nystagmus whose astigmatic refractive error was -1.50 D or less, nystagmus intensity (amplitude x frequency) correlated significantly with acuity for optotypes (r = 0.71), but not for gratings. Although resolution for vertical gratings was correlated with astigmatic refractive correction, the ratio of resolution for gratings parallel and orthogonal to the meridian of nystagmus was not. Thus, the belief that poorer acuity in patients with substantial astigmatism is attributable to an optically induced meridional amblyopia is supported only partly by these results. The authors concluded that among patients with congenital nystagmus, the influence of eye motion on visual acuity is not readily predicted either from the parameters of nystagmus that they evaluated or from the comparison of resolution for horizontal and vertical gratings.     

Directional asymmetry of the horizontal monocular head and eye optokinetic nystagmus: effects of picrotoxin

Frog monocular eye and head optokinetic nystagmus (OKN) were studied by coil recordings after intravitreal administration of picrotoxin into the closed eye. Before injection, the frog displayed an OKN only for stimulations in the temporo-nasal (T-N) direction. The injection of picrotoxin provoked the appearance of a N-T component of the head and eye OKN: the slow phase velocity gain and the resetting fast phase frequency were strongly and significantly increased. Thus, picrotoxin abolished the directional asymmetry of head and eye OKN, indicating the involvement of GABAergic mechanisms in the inhibition of the N-T component of the monocular eye and head OKN. Picrotoxin administration had an additional effect on the monocular head OKN only, the performances (measured by the velocity gain and the frequency of resetting fast phases) were markedly increased for both directions of stimulation, suggesting an effect of the drug upon the motor output of head movements.     

The cerebellum in eye movement control: nystagmus,coordinate frames and disconjugacy

In this review we discuss several aspects of eye movement control in which the cerebellum is thought to have a key role, but have been relatively ignored. We will focus on the mechanisms underlying certain forms of cerebellar nystagmus, as well as the contributions of the cerebellum to binocular alignment in healthy and diseased states. A contemporary review of our understanding provides a basis for directions of further inquiry to address some of the uncertainties regarding the contributions of the cerebellum to ocular motor control.The cerebellum is an important structure within a widely distributed neural network that controls movements including those of the eyes. Both the immediate online control of movement and the adjustments necessary to optimize motor performance in the long term are under its purview. Not surprisingly, ocular motor abnormalities are prominent on clinical examination of most cerebellar patients. Attempts to localize particular eye movement abnormalities to specific parts of the cerebellum—traditional clinical–anatomical localization—combined with results of experimental lesions in animals, have led to inferring functions to specific cerebellar structures. While these approaches facilitate topical diagnosis, they do not necessarily translate to a better understanding of the specific role of the cerebellum in eye movement control. In fact, we are still relatively ignorant about how the cerebellum performs its functions. Here, we will consider the role of the cerebellum in binocular control—both to create disconjugacy when it is necessary, and to prevent ocular misalignment when it is unnecessary and disruptive. We will also touch on the implications of evolving into frontal-eyed creatures, with the competing demands of binocular, foveal vs retinal, full-field stabilization of images. Furthermore, we suggest that the phylogenetically old vestibular anlage persists in a rudimentary form within our human brains and its vestiges can be uncovered in neurological disease.^{1, 2, 3, 4} These issues bear on interpretation of pathological nystagmus, which depends on the coordinate system in which the nystagmus is couched (foveal: eye frame vs full-field retina: head frame), and also on the types of ocular misalignment seen in cerebellar patients.     

The relationship between head and eye movement in congenital nystagmus with head shaking: objective recordings of a single case.

Head shaking and congenital nystagmus were recorded in a patient presented with visual tasks. When she was at rest the nystagmus took a 6 cycles per second saw-tooth wave-form. When she was attentive the nystagmus beat at a 2 to 2.6 cycles per second with a saddle-shaped deformation which permitted foveation. The head shaking occurred occasionally when the patient was attentive and was phase-locked to the nystagmus with resemblances in wave form and direction. Deceleration of the head shaking to zero velocity and peak displacement (to the left) coincided with the onset of the saddle of the nystagmus and hence assisted foveation; all other parts of the head-shaking cycle were detrimental to vision. It is proposed that the head shaking has a common pathological origin with the nystagmus and that, just as an isolated congenital nystagmus wave form becomes altered with attention to permit periods of foveal fixation, the pattern of combined head and eye nodding in this patient provided similar peroids of fixation.     

先天性眼球震颤眼球运动波形的相图特点分析

背景 先天性眼球震颤患者的眼球运动波形表现各异,其时间动力学的非线性特征复杂,常规的时间序列波形图不便于对患者进行临床诊断及评估.眼球运动系统是非线性反馈控制系统,而相图法是一 种用于描绘非线性系统运动特征的分析技术,但相图法在先天性眼球震颤检测中的应用尚未见报道. 目的尝试建立先天性眼球震颤眼球运动波形的相图法分析技术,为先天性眼球震颤的临床诊断与定量评估提供新的方法.方法 采用前瞻性病例观察设计,纳入2012年4月至2013年2月在天津市眼科医院就诊的25例先天性眼球震颤患者,其中先天性运动性眼球震颤(CMN)患者12例,隐性眼球震颤(LN)患者13例.所有患者行视频眼动图(VOG)检查,对VOG数据进行格式转换后,采用Matlab程序对数据进行处理,得到每个眼动波形周期的相位图,并从相位图上测得周期位移(CPS)、慢相峰值速度(SPV)及其标准化值(SSPV)、快相峰值速度(FPV)及其标准化值(SFPV).比较先天性眼球震颤波形速度递增型和速度递减型的测量参数.结果 先天性眼球震颤的眼球运动相图呈现周期性规律性往复运动轨迹,其慢相过程表现为密集带状轨迹,快相过程表现为稀疏环状轨迹.CMN的眼球运动波形以速度递增型为主,而LN的眼球运动波形以速度递减型为主,2种波形相图轨迹走行均呈顺时针方向.速度递增型CPS、SPV及FPV分别为(4.646±1.565)、(223.821±114.049)和(767.481±263.560)°/s,速度递减型CPS、SPV及FPV分别为(9.373±4.189)、(357.531±154.300)和(1 148.706±541.362)°/s;速度递增型中SPV和FPV与CPS间均呈显著正相关(rSPV-CPS=0.685,P=0.000;rFPV-CPS=0.680,P=0.000);速度递减型中SPV和FPV与CPS间均呈显著正相关(rSPV-CPS=0.783,P=0.000;rFPV-CPS=0.803,P=0.000).2种波形FPV均大于SPV,差异均有统计学意义(速度递增型:t=6.558,P=0.000;速度递减型:t=5.068,P=0.000).速度递增型SSPV为(48.062±15.365)°/s,略大于速度递减型的(41.099±17.027)°/s,但差异无统计学意义(t=1.070,P=0.296);速度递增型SFPV为(171.186±47.825)°/s,大于速度递减型的(125.317±38.266)°/s,差异有统计学意义(t=2.658,P=0.014).结论 相图法能够直观显示先天性眼球震颤眼球运动轨迹的周期性动态特征,便于测量其不同时相的运动幅度、速度等参数.     

Involvement of ON and OFF retinal channels in the eye and head horizontal optokinetic nystagmus of the frog

The specific role of ON and OFF retinal information channels in the generation of the horizontal optokinetic nystagmus (OKN) of the frog was studied. Coil recordings of monocular eye and head OKN were obtained before and after intravitreal injection of two drugs that block either ON or OFF channels. The intravitreal injection of 2-amino-4-phosphonobutyrate (APB), a glutamate analog that selectively blocks the ON retinal channel, strongly reduced or even cancelled the monocular OKN of the head and of the eye. The intravitreal injection of another glutamate analog, the cis-2,3-piperidine dicarboxylic acid (PDA) that especially blocks the OFF retinal channel, did not affect the gain velocity of the slow phase of both the horizontal monocular head and eye OKN, for low stimulus velocities. Our results suggest that the retinal ON information channel, but not the OFF channel, is involved in the generation of the slow phase of the OKN of the frog, at least at low drum velocities.     

Maldevelopment of convergence eye movements in macaque monkeys with small- and large-angle infantile esotropia

PURPOSE: To describe symmetric convergence eye movements evoked by disparity and/or accommodative cues in esotropic macaque monkeys, with the goal of determining whether these animals have the vergence deficits found in humans with esotropia. METHODS: Physical far and near targets were used to evoke large (approximately 8 degrees) symmetric convergence eye movements in four adult macaque monkeys (two with strabismus, two normal), using positive-feedback rewards. One strabismic monkey had infantile-onset, small-angle esotropia (small-eso approximately 2 degrees) induced by alternating occlusion from birth to age 9 months. The other strabismic monkey had naturally occurring, large-angle (approximately 25 degrees) infantile-onset esotropia (large-eso). Visual acuity was normal in each eye as measured by spatial sweep visually evoked potentials (VEPs). Eye movements were recorded using magnetic search coils. RESULTS: When viewing binocularly, both normal monkeys exhibited accurate, stereotyped symmetric convergence movements that achieved 87% to 96% of the required change in vergence angle by the end of the initial movement. In contrast, the small-eso monkey's convergence response when viewing binocularly was variable, strikingly asymmetric, usually accompanied by a disjunctive saccade, and subnormal, achieving only 56% of required vergence. The convergence response of the large-eso monkey was also asymmetric and weak, achieving 18% of the required vergence and employing conjugate saccades to refixate the near target. Monocular viewing (i.e., accommodative vergence) caused substantial reductions in both convergence amplitudes and velocities in the normal monkeys, but had a minor effect on the vergence behavior of the strabismic animals. CONCLUSIONS: Monkeys with small- and large-angle infantile esotropia have striking maldevelopments of binocular (disparity-driven) convergence and use accommodative vergence and saccades to refixate near targets. Their vergence behavior resembles that in esotropic humans. The maldevelopment may be explained in large part by the paucity of binocular connections recently described in the visual cortex of esotropic macaques.     

Eye movement baseline oscillation and variability of eye position during foveation in congenital nystagmus

Despite the inability to maintain steady fixation, congenital nystagmus does not necessarily reduce visual acuity, that can be achieved during the foveation periods. The duration of the foveation period, but also the cycle-to-cycle variability of eye position and velocity during foveations play an important role. A quantitative relationship that relates visual acuity with foveation time and cycle-to-cycle variability of eye position during foveation has been previously proposed. In many infrared-oculographic and electro-oculographic eye position recordings of our database, a sinusoidal-like oscillation of the baseline was observed, on which the nystagmus waveforms lay. This oscillation may contribute to increase cycle-to-cycle variability during foveations. The aim of this work is to extract the baseline oscillation from the recordings and to verify its relationship with eye position variability during foveation. On the basis of the observations, the baseline oscillation was assumed to be sinusoidal, and was estimated (using a least mean square technique) from eye movement signals recorded during fixation intervals, at different gaze positions, from 20 patients affected by congenital nystagmus with low visual acuity. The average baseline oscillation amplitude was 1.31°, while the average frequency was 0.34 Hz. Baseline oscillation amplitude was well correlated (with a coefficient of 0.66) to the standard deviations of eye-position during foveation, which in turn is connected to visual acuity.     

Age related change of optokinetic nystagmus in healthy subjects: a study from infancy to senescence

BACKGROUND: Optokinetic nystagmus (OKN) gain is asymmetrical between temporal to nasal (TN) and nasal to temporal (NT) stimulation in infancy and decreases at older ages. The age at which OKN gain becomes symmetrical and decreases is debated. The aim was to investigate OKN over the whole lifespan in a large sample of healthy subjects. METHODS: In a prospective, cross sectional study OKN was tested monocularly using TN and NT small field stimulation. Stimulation velocity was 15 degrees /s and 30 degrees /s for children aged under 1 year (n = 97), and 15 degrees /s, 30 degrees /s, 45 degrees /s, and 60 degrees /s for older subjects (1-9 years, n = 66; 10-89 years, n = 86). Gain was measured using infrared oculography. RESULTS: Significant OKN gain asymmetry in favour of TN versus NT stimulation was found during the first 5 months of life (p<0.05). Only at 11 months of age was OKN symmetrical in 100% of the subjects. The percentage of children with symmetrical OKN decreased with increasing stimulus velocity. OKN gain increased in the second and third years (p<0.05 for 15 degrees /s), remained stable until 50 years of age, and showed a small but significant decrease afterwards for the tested velocities (between 6% and 18%, p<0.05). CONCLUSIONS: Infrared oculography is an accurate method to assess OKN, especially in children. Knowledge about change of OKN in healthy subjects could be helpful to interpret OKN in patients with abnormal binocular vision or lesions of the central nervous system.     

Relationship between visual acuity and eye position variability during foveations in congenital nystagmus

Visual acuity in congenital nystagmus has proven to be primarily related to the duration of foveation periods, during which the image of a target falls onto the fovea and eye velocity slows down. It was found that the longer the foveation time the higher the visual acuity. However, the cycle-to-cycle variability of the eye position and velocity during foveation periods also contribute to visual acuity. A high variability of the eye position during the foveations hinders a stable placement of the target image on the centralmost fovea and consequently decreases visual acuity. To investigate the relationship between different nystagmus features and visual acuity, infrared- oculographic and electro-oculographic eye position recordings of 20 patients affected by congenital nystagmus were analysed in different gaze positions. In several patients' recordings, a high variability of the eye position during foveations (i.e. greater than 0.5°) was detected. Correspondingly, low visual acuity was measured, in spite of sufficiently long foveation periods. The standard deviation of eye positions during foveation periods was used to measure this variability and it was found to be correlated to visual acuity, in conjunction with the mean duration of the foveation periods. On the basis of the data analysis, an exponential relationship is proposed to relate visual acuity and the standard deviation of the eye position during foveations.     

利用视动性转鼓视力仪对豚鼠色觉和对比度视力的检测

目的 研发一种可以快速定量检测动物的对比敏感度视力、色觉的装置,并用该装置来评价豚鼠的对比敏感度视力和色觉.方法 实验研究.根据豚鼠视细胞的光谱敏感性函数曲线,选取绿、蓝、黄三种不同颜色,制作绿-白、蓝-白和黄-绿三种颜色组合且空间频率均为0.6 c/d的方波条栅视标,每种颜色组合的条栅视标分别又具有高、中、低三种对比度.对于黑白方波条栅,选用3.0 c/d空间频率,制作对比度分别为100%、50%、25%的条栅.将条栅视标贴附在可以转动的圆形鼓内壁,利用豚鼠对运动物体会产生有规律的视动性头部追随运动这一生理现象,在受试豚鼠保持清醒的自然状态下,用视动性转鼓视力仪来初步检测豚鼠的色觉及对比敏感度视力.采用非参数检验中的Kruskal-Wallis检验分析豚鼠在不同对比度下的头部运动追随率.结果 用视动性转鼓视力仪,可以在行为学上验证豚鼠的色觉.豚鼠对空间频率为0.6 c/d的绿、蓝、黄三种颜色组合的方波条栅表现出良好的头部追随运动,在低对比度下,豚鼠的头部运动追随率分别为1.06±0.14（实际对比度为2.41%）、1.12±0.17（实际对比度为1.87%）、1.05±0.15（实际对比度为6.50%）.对于空间频率为3.0 c/d的黑白方波条栅,当对比度降到25%时,豚鼠仍可表现出明确的头部追随运动,其头部运动追随率为0.74±0.08,与高对比度条栅下的追随率经非参数检验分析,差异无统计学意义（x2=2.47,P＞0.05）.结论 转鼓视力仪可以检测豚鼠的颜色视觉并定量确定其颜色对比敏感度视力.该实验装置及实验流程操作简单,可以用于豚鼠色觉和视力的检查.     

Eight eye muscle surgical treatment in a patient with acquired nystagmus and strabismus: a case report

The purpose of this paper is to outline the clinical benefits and electrophysiological changes after extraocular muscle surgery for acquired nystagmus and strabismus in an adult patient. a 41-year-old Caucasian female suffered from oscillopsia, bilateral cranial nerve IV palsies, and vertical nystagmus. Medical therapy was ineffective. She underwent bilateral, eight muscle surgical procedure which included: tenectomies of the superior oblique OU, myectomies of the inferior oblique OU, recessions of the medial rectus muscles OU (with OD on a post-operatively adjustable suture), and differential recessions of the superior rectus muscles OU. This provided marked improvement in her symptoms. These results suggest that surgery for acquired nystagmus can affect an improvement in the characteristics of the nystagmus that result in visual complaints. Combining "nystagmus surgery" plus strabismus surgery may be a viable option in some adult patients with acquired nystagmus who are unresponsive to medical therapy.