Diplopia and eye movement disorders.

Published versio

Application of zebrafish oculomotor behavior to model human disorders

To ensure high acuity vision, eye movements have to be controlled with astonishing precision by the oculomotor system. Many human diseases can lead to abnormal eye movements, typically of the involuntary oscillatory eye movements type called nystagmus. Such nystagmus can be congenital (infantile) or acquired later in life. Although the resulting eye movements are well characterized, there is only little information about the underlying etiology. This is in part owing to the lack of appropriate animal models. In this review article, we des­cribe how the zebrafish with its quick maturing visual system can be used to model oculomotor pathologies. We compare the characteristics and assessment of human and zebrafish eye movements. We describe the oculomotor properties of the zebrafish mutant belladonna, which has non-crossing optical fibers, and is a particularly informative model for human ocu­lomotor deficits. This mutant displays a reverse optokinetic response, spontaneous oscillations that closely mimic human congenital nystagmus and abnormal motor behavior linked to circular vectio

Aerospace medicine and biology. A continuing bibliography (supplement 231)

This bibliography lists 284 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1982

Suppression of displacement in severely slowed saccades

Severely slowed saccades in <I>spinocerebellar ataxia</I> have previously been shown to be at least partially closed-loop in nature: their long duration means that they can be modified in-flight in response to intrasaccadic target movements. In this study, a woman with these pathologically slowed saccades could modify them in-flight in response to target movements, even when saccadic suppression of displacement prevented conscious awareness of those movements. Thus saccadic suppression of displacement is not complete, in that it provides perceptual information that is sub-threshold to consciousness but which can still be effectively utilised by the oculomotor system

Human optokinetic nystagmus: a stochastic analysis.

Optokinetic nystagmus (OKN) is a fundamental gaze-stabilizing response found in almost all vertebrates, in which eye movements attempt to compensate for the optic flow caused by self-motion. It is an alternating sequence of slow compensatory eye movements made in the direction of stimulus motion and fast eye movements made predominantly in the opposite direction. The timing and amplitude of these slow phases (SPs) and quick phases (QPs) are remarkably variable, and the cause of this variability is poorly understood. In this study principal components analysis was performed on OKN data to illustrate that the variability in correlation matrices across individuals and recording sessions reflected changes in the noise in the system while the linear relationships between variables remained predominantly the same. Three components were found that could explain the variance in OKN data, and only variables from within a single cycle contributed highly to any given component. A linear stochastic model of OKN was developed based on these results that describes OKN as a triple first order Markov process, with three sources of noise affecting SP velocity, the QP trigger, and QP amplitude. This model was used to predict the degree of signal dependent noise in the system, the duration of the transient state of SP velocity, and an apparent undershoot bias to the QP target location

Oculomotor Control in Patients with Parkinson\u27s Disease

There have been few studies investigating the eye movement behavior of Parkinson’s disease patients during fixation. This study objectively measured the eye movements of 36 patients with Parkinson’s disease, and 20 age matched controls. Stimuli consisted of ten standardized text passages first organized by Miller and Coleman. In addition, subjects followed a randomly displaced step jump target motion. Pendular nystagmus was found in all Parkinson’s subjects, with an average frequency of 7.44 Hz. Saccadic peak velocity and duration along the main sequence were not statistically different from controls. A slower rate of reading was also noted in the Parkinson’s group in terms of characters per minute, but with no more regressions than normal. Rate of square wave jerks was also found to be normal. This suggests that the hallmark feature of eye movements in Parkinson’s disease is a pendular nystagmus during fixation, and all saccadic activity to be normal

A molecular-genetic study of Congenital Nystagmus

Nystagmus is a disorder of eye movement characterised by irregular, uncontrolled and repetitive eye movements. It can occur in a broad spectrum of clinical situations and diseases or it may occur in isolation and an inherited disorder. Surprisingly little is known about the underlying mechanisms of ocular-motor control. Similarly, the pathophysiological mechanisms underpinning nystagmus is also poorly understood. By studying pedigrees in whom nystagmus seems to be inherited as an isolated trait (Congenital Idiopathic Nystagmus), it may be possible to identify some of the genetic causes of this disorder and subsequently understand the pathophysiology.This thesis describes a molecular genetic study of congenital nystagmus. A clinical phenotyping study is followed by linkage analysis and positional cloning. A novel nystagmus gene is investigated in a large cohort of Congenital Idiopathic Nystagmus (CIN) patients and X-inactivation studies are performed. Subsequently, cell culture and RT-PCR work is performed to study expression of this gene. Additionally a pedigree with an atypical congenital nystagmus disorder is investigated and a new mutation within a known cerebellar disease gene is identified.This work contributed to the identification of the first gene for Congenital Idiopathic Nystagmus (CIN). The first detailed temporal expression study of the FRMD7 nystagmus gene was also performed in this study which has directed further studies into the pathogenesis of CIN. Identification of a new mutation in the CACNA1A gene in a pedigree with nystagmus and subtle cerebellar signs has lead to the consideration of this gene in patients who present to hospital with isolated atypical nystagmus

Eye tracking in optometry: A systematic review

This systematic review examines the use of eye-tracking devices in optometry, describing their main characteristics, areas of application and metrics used. Using the PRISMA method, a systematic search was performed of three databases. The search strategy identified 141 reports relevant to this topic, indicating the exponential growth over the past ten years of the use of eye trackers in optometry. Eye-tracking technology was applied in at least 12 areas of the field of optometry and rehabilitation, the main ones being optometric device technology, and the assessment, treatment, and analysis of ocular disorders. The main devices reported on were infrared light-based and had an image capture frequency of 60 Hz to 2000 Hz. The main metrics mentioned were fixations, saccadic movements, smooth pursuit, microsaccades, and pupil variables. Study quality was sometimes limited in that incomplete information was provided regarding the devices used, the study design, the methods used, participants' visual function and statistical treatment of data. While there is still a need for more research in this area, eye-tracking devices should be more actively incorporated as a useful tool with both clinical and research applications. This review highlights the robustness this technology offers to obtain objective information about a person's vision in terms of optometry and visual function, with implications for improving visual health services and our understanding of the vision process

Purkinje image eyetracking: A market survey

The Purkinje image eyetracking system was analyzed to determine the marketability of the system. The eyetracking system is a synthesis of two separate instruments, the optometer that measures the refractive power of the eye and the dual Purkinje image eyetracker that measures the direction of the visual axis

The Fourier analysis of saccadic eye movements

This thesis examines saccadic eye movements in the frequency domain and develops sensitive tools for characterising their dynamics. It tests a variety of saccade models and provides the first strong empirical evidence that saccades are time-optimal. By enabling inferences on the neural command, it also allows for better clinical differentiation of abnormalities and the evaluation of putative mechanisms for the development of congenital nystagmus. Chapters 3 and 4 show how Fourier transforms reveal sharp minima in saccade frequency spectra, which are robust to instrument noise. The minima allow models based purely on the output trajectory, purely on the neural input, or both, to be directly compared and distinguished. The standard, most commonly accepted model based on bang-bang control theory is discounted. Chapter 5 provides the first empirical evidence that saccades are time-optimal by demonstrating that saccade bandwidths overlap across amplitude onto a single slope at high frequencies. In Chapter 6, the overlap also allows optimal (Wiener) filtering in the frequency domain without a priori assumptions. Deconvolution of the aggregate neural driving signal is then possible for current models of the oculomotor plant. The final two chapters apply these Fourier techniques to the quick phases of physiological (optokinetic) nystagmus and of pathological (congenital) nystagmus. These quick phases are commonly assumed to be saccadic in origin. This assumption is thoroughly tested and found to hold, but with subtle differences implying that the smooth pursuit system interacts with the saccade system during the movement. This interaction is taken into account in Chapter 8 in the assessment of congenital nystagmus quick phases, which are found to be essentially normal. Congenital nystagmus models based on saccadic abnormalities are appraised