The objective assessment of abnormal eye movements in infants and young children

The natural history of ataxia-telangiectasia (A-T): A systematic review

BACKGROUND

Ataxia-telangiectasia is an autosomal recessive, multi-system, and life-shortening disease caused by mutations in the ataxia-telangiectasia mutated gene. Although widely reported, there are no studies that give a comprehensive picture of this intriguing condition.

OBJECTIVES

Understand the natural history of ataxia-telangiectasia (A-T), as reported in scientific literature.

SEARCH METHODS

107 search terms were identified and divided into 17 searches. Each search was performed in PubMed, Ovid SP (MEDLINE) 1946-present, OVID EMBASE 1980 -present, Web of Science core collection, Elsevier Scopus, and Cochrane Library.

SELECTION CRITERIA

All human studies that report any aspect of A-T.

DATA COLLECTION AND ANALYSIS

Search results were de-duplicated, data extracted (including author, publication year, country of origin, study design, population, participant characteristics, and clinical features). Quality of case-control and cohort studies was assessed by the Newcastle-Ottawa tool. Findings are reported descriptively and where possible data collated to report median (interquartile range, range) of outcomes of interest.

MAIN RESULTS

1314 cases reported 2134 presenting symptoms. The most common presenting symptom was abnormal gait (1160 cases; 188 studies) followed by recurrent infections in classical ataxia-telangiectasia and movement disorders in variant ataxia-telangiectasia. 687 cases reported 752 causes of death among which malignancy was the most frequently reported cause. Median (IQR, range) age of death (n = 294) was 14 years 0 months (10 years 0 months to 23 years 3 months, 1 year 3 months to 76 years 0 months).

CONCLUSIONS

This review demonstrates the multi-system involvement in A-T, confirms that neurological symptoms are the most frequent presenting features in classical A-T but variants have diverse manifestations. We found that most individuals with A-T have life limited to teenage or early adulthood. Predominance of case reports, and case series demonstrate the lack of robust evidence to determine the natural history of A-T. We recommend population-based studies to fill this evidence gap.

Vision and sensorimotor defects associated with loss of Vps11 function in a zebrafish model of genetic leukoencephalopathy

Genetic Leukoencephalopathies (gLEs) are heritable white matter disorders that cause progressive neurological abnormalities. A founder mutation in the human endolysosomal trafficking protein VPS11 has been identified in Ashkenazi Jewish patients manifesting classic gLE symptoms of hypomyelination, developmental delay, motor and systemic deficits. In this study, we characterized the visual and sensorimotor function of two zebrafish vps11 mutant lines: the previously reported vps11(plt), and a new vps11(-/-) null mutant line, using behavioral analysis to track larval motor responses to visual and acoustic stimuli. We found that mutant larvae from both vps11(plt) and vps11(-/-) lines were able to visually distinguish light and dark, but showed a progressive loss of a normal sensorimotor response to visual stimuli from 5 days post fertilization (dpf) to 7dpf. Additionally, optokinetic response analysis performed at 5dpf indicated that the mutants were significantly visually impaired. Both mutant lines also displayed a progressively lower sensorimotor response to a singular acoustic stimulus from 5-7dpf. Next, we tested the habituation response of the mutant lines to series of acoustic taps. We found both mutant lines habituated faster than their siblings, and that vps11(plt) mutants habituated faster than the vps11(-/-) mutants. Together, these data suggest that loss of Vps11 function results in progressive visual and sensorimotor abnormalities in the zebrafish vps11(plt) and vps11(-/-) mutant lines. This is the first study to characterize behavioral deficits in a vertebrate model of Vps11-dependent gLE. The mutants and behavioral assays described here could be a valuable model system in which to test potential pharmacological interventions for gLE.

Ocular Motor Score (OMS): a clinical tool to evaluating ocular motor functions in children. Intrarater and inter-rater agreement

PURPOSE

Ocular motor score (OMS) is a new clinical test protocol for evaluating ocular motor functions in children and young adults. OMS is a set of 15 important and relevant non-invasive ocular motor function parameters derived from clinical practice. The aim of the study was to evaluate OMS according to intrarater and inter-rater agreement.

METHODS

Forty children aged 4-10 years, 23 girls median age 6.5 (range 4.3-9.3) and 17 boys median age 5.8 (range 4.1-9.8) were included. The ocular motor functions were assessed and scored according to the OMS protocol. The examinations were videotaped. To obtain the intrarater agreement, the first author examined and scored the children twice, first in the clinic and 2 weeks later by watching the videotape. To obtain the inter-rater agreement, three other raters independently scored the ocular motor function of the children by watching the videotapes.

RESULTS

The overall observed intrarater agreement was 88%, and the observed inter-rater agreement between the three raters was 80%. For none of the subtests was there an observed intrarater agreement lower than 65%. Three of the subtests had an observed inter-rater agreement of 65% or below.

CONCLUSION

Overall there was high observed intra- and inter-rater agreement for the OMS test protocol. Subtests such as saccades and smooth pursuit were more difficult for raters to score similarly according the clinical OMS test protocol.

Ocular motor score a novel clinical approach to evaluating ocular motor function in children

PURPOSE

Ocular motility disturbances are common in a number of neuropaediatric and neurometabolic disorders. Assessment of ocular motor function can be a source of information for diagnosis and follow-up of these patients.

AIM

To evaluate a new clinical ocular motor function test: ocular motor score (OMS) and provide reference values in children and young adults without known ocular or neurological disorders.

MATERIAL AND METHODS

A total of 233 children and young adults, 103 males and 130 females between the ages of 6 months and 19 years, were assessed according to a specific OMS protocol. They were divided into four different age groups: 0.5-3, 4-6, 7-10 and 11-19 years. The OMS protocol consists of 15 different subtests evaluating ocular motor function, and a total score of minimum 0 up to max 15 can be obtained: the minimum score, 0, is considered normal while 1 represents an abnormal function.

RESULTS

The median OMS in the whole reference group was 0.3 (range 0-4.8). The median OMS in the different age groups, starting with the youngest, was: 0.9 (range 0.3-4.8), 0.3 (range 0-3.4), 0.3 (range 0-2.3) and 0 (range 0-3.5), respectively. The youngest subjects, aged 0.5-3, showed a significantly higher total OMS compared with the other age groups (p < 0.001).

CONCLUSION

This study provides reference values for the OMS test in a population aged 0.5-19 years. The test may be valuable as a screening tool for identification and follow-up of ocular motor dysfunction in children and young adults.

Saccades in children

Saccades are necessary for optimal vision. Little is known about saccades in children. We recorded saccades using an infrared eye tracker in 39 children, aged 8-19 years. Participants made saccades to visual targets that stepped 10 degrees or 15 degrees horizontally and 5 degrees or 10 degrees vertically at unpredictable time intervals. Saccadic latency decreased significantly with increasing age, while saccadic gain and peak velocity did not vary with age. Saccadic gains and peak velocities in children are similar to reported adult values. This implies maturity of the neural circuits responsible for making saccades accurate and fast. Saccade latency decreases as the brain matures.

A model of neuronopathic Gaucher disease

Gaucher disease (GD) is a lysosomal disorder involving the accumulation of glucocerebroside in the liver, spleen, bones and brain. Some patients exhibit only systemic disease (type I), but others have additional neurological signs which may lead to rapid neurodegeneration in infancy (type II) or take a more intermediate course (type III). Types II and III are collectively known as neuronopathic Gaucher disease (NGD). Systemic disease can now be treated by enzyme replacement therapy (ERT), but its efficacy in NGD is limited. Two infants who presented with bulbar palsy and failure to thrive were enzymatically diagnosed at 8 months with NGD. They were started on high-dose ERT (120 IU/kg every 2 weeks). Both underwent serial oculomotor assessment and an audiological battery, including visual reinforcement audiometry, otoacoustic emissions, and the auditory brain stem response (ABR). Biochemical markers showed an incomplete systemic response to ERT, but neurological deterioration was relentless, leading to death at 16 and 25 months. Oculomotor testing revealed a complete absence of saccadic eye movements and progressive bilateral sixth nerve palsy in one. Audiological assessment revealed progressive deterioration of ABRs, but with normal peripheral hearing and otoacoustic emissions. Both infants showed neurological deterioration in spite of high-dose ERT. The audiological findings suggested a loss of inner hair cell pathway function with preserved outer hair function, similar to what is seen in auditory neuropathy. The unusual pattern of audiological and oculomotor abnormalities is consistent with an excitotoxic mechanism predisposing nerve cells to glucocerebroside toxicity. Such excitotoxic damage may be amenable to direct therapeutic intervention.

Abnormal supranuclear eye movements in the child: a practical guide to examination and interpretation

Abnormal eye movements in the infant or voting child can be congenital or acquired. They may be a result of abnormal early visual development or a sign of underlying neurologic or neuromuscular disease. It is important to be able to detect these abnormalities and to distinguish them from normal but immature eye movements. The spectrum of disease in children differs from that in adults. Serious, potentially fatal but treatable disorders can be acquired in infancy, and abnormal eye movements in a sometimes apparently well child should never be labeled as congenital or benign without careful investigation. Eye movement analysis can indicate the presence of an underlying condition and help the clinician to classify different neurologic diseases. It is important to carefully examine the ocular motor system in any children at risk of neurologic disease. This review provides a practical guide to the examination and interpretation of eye movements in the child and includes recent literature on eye movement disorders of childhood. We describe supranuclear abnormalities of the ocular motor system in the order in which we would normally examine it: saccades, pursuit, convergence, vestibulo-ocular reflex, and optokinetic nystagmus. Nystagmus, internuclear ophthalmoplegia, cranial nerve abnormalities, and "miswiring" phenomena (such as Duane's syndrome and synergistic divergence) are not discussed.

Vertical or asymmetric nystagmus need not imply neurological disease

AIM

To indicate that congenital idiopathic nystagmus (CIN) and sensory defect nystagmus (SDN) can be vertical or asymmetric in some children.

METHODS

Of 276 children presenting with nystagmus for electrophysiological testing, 14 were identified as having CIN or SDN, yet had a nystagmus which was either vertical (n=11) or horizontal asymmetric (n=3). Flash electroretinograms and flash and pattern visual evoked potentials (VEPs) were recorded in all patients. Eye movement assessment, including horizontal optokinetic nystagmus (OKN) testing, was carried out in 11/14 patients.

RESULTS

Eight patients (seven with vertical, one with asymmetric horizontal nystagmus) had congenital cone dysfunction. One patient with vertical and another with asymmetric nystagmus had cone-rod dystrophy. One patient with vertical upbeat had congenital stationary night blindness. Two patients (one downbeat, one upbeat nystagmus) had normal electrophysiological, clinical, and brain magnetic resonance imaging findings and were classified as having CIN. One patient with asymmetric nystagmus showed electrophysiological and clinical findings associated with albinism. Horizontal OKN was present in 80% of patients tested, including the three cases with horizontal asymmetric nystagmus. This is atypical in both CIN and SDN, where the OKN is usually absent.

CONCLUSIONS

Vertical and asymmetric nystagmus are most commonly associated with serious intracranial pathology and its presence is an indication for neuroimaging studies. However, such nystagmus can occur in children with retinal disease, albinism, and in cases with CIN. These findings stress the importance of non-invasive VEP/ERG testing in all cases of typical and also atypical nystagmus.

Smooth pursuit development in infants

PURPOSE

We set out to assess the development of pursuit eye movements in normal infants in an objective, longitudinal fashion. We asked whether smooth pursuit (SP) was present under 2 months of age and how the saccade ratio changed with increasing infant age.

METHODS

Smooth pursuit was recorded longitudinally from 25 infants aged 1-7 months, using DC electro-oculography, in a clinically practical manner. Four uninstructed adults acted as controls.

RESULTS

Smooth pursuit was present under 2 months of age. The gain of SP increased with increasing infant age. However, it had still not reached adult levels by 6 months of age. Latency decreased with increasing infant age. Monocular SP asymmetry was present in the younger infants.

CONCLUSIONS

Smooth pursuit is present under 2 months of age, but at 6 months SP has still not reached adult levels. The traditional model of SP development is questionable.

Intermittent horizontal saccade failure ('ocular motor apraxia') in children

BACKGROUND

Ocular motor apraxia (OMA) in childhood is a poorly understood condition involving a failure of horizontal saccades. OMA is thought to be rare but the literature indicates wide clinical associations. OMA is often identified by abnormal head movements, but failure of reflexive quick phases has been reported in all but a few patients. The extent of this oculomotor disorder was examined in a large group of children with diverse clinical backgrounds.

METHODS

The degree of quick phase failure during horizontal vestibular and optokinetic nystagmus was measured using DC electro-oculography and video in 74 affected children, aged 17 days to 14 years.

RESULTS

All children showed an intermittent failure of nystagmic quick phases, except for total failure in one case. Other visuomotor abnormalities were common including saccadic hypometria (85%), low gain smooth pursuit (70%), neurological nystagmus (28%), strabismus (22%), and vertical abnormalities (11%). Non-ocular abnormalities were common including infantile hypotonia (61%), motor delay (77%), and speech delay (87%). There was a wide range of clinical associations including agenesis of the corpus callosum, Joubert syndrome, Dandy-Walker malformation, microcephaly, hydrocephalus, vermis hypoplasia, porencephalic cyst, megalocephaly, Krabbe leucodystrophy, Pelizaeus Merzbacher disease, infantile Gaucher disease, GM1 gangliosidosis, infantile Refsum's disease, propionic acidaemia, ataxia telangiectasia, Bardet-Biedl syndrome, vermis astrocytoma, vermis cyst, carotid fibromuscular hypoplasia, Cornelia de Lange syndrome, and microphthalmos. Perinatal and postnatal problems were found in 15% including perinatal hypoxia, meningitis, periventricular leucomalacia, athetoid cerebral palsy, perinatal septicaemia and anaemia, herpes encephalitis, and epilepsy. Only 27% were idiopathic.

CONCLUSION

Quick phase failure is a constant feature of OMA, whereas abnormal head movements were detected in only about half, depending on the underlying diagnosis. This oculomotor sign is better described as an intermittent saccade failure rather than as a true apraxia. It indicates central nervous system involvement, has wide clinical associations, but it is not a diagnosis.

Delayed visual maturation in infants: a disorder of figure-ground separation?

Delayed visual maturation (DVM) is characterised by visual unresponsiveness in early infancy, which subsequently improves spontaneously to normal levels. We studied the optokinetic response and recorded pattern reversal VEPs in six infants with DVM (aged 2-4 months) when they were at the stage of complete visual unresponsiveness. Although no saccades or visual tracking with the eyes or head could be elicited to visual objects, a normal full-field rapid buildup OKN response occurred when viewing biocularly or during monocular stimulation in the temporo-nasal direction of the viewing eye. Almost no monocular OKN could be elicited in the naso-temporal direction, which was significantly poorer than normal age-matched infants. No OKN quick phases were missed, and there were no other signs of "ocular motor apraxia." VEPs were normal in amplitude and latency for age. It appears, therefore, that infants with DVM are delayed in orienting to local regions of the visual field, but can respond to full-field motion. The presence of normal OKN quick-phases and slow-phases suggests normal brain stem function, and the presence of normal pattern VEPs suggests a normal retino-geniculo-striate pathway. These oculomotor and electrophysiological findings suggest delayed development of extra-striate cortical structures, possibly involving either an abnormality in figure-ground segregation or in attentional pathways.

Electrophysiological and eye-movement abnormalities in children with the Bardet-Biedl syndrome

We investigated 17 patients with clinical features of Bardet-Biedl syndrome by electroretinogram (ERG), visual-evoked potentials (VEP), and electro-oculographic (EOG) eye movement assessment. The ERGs were grossly abnormal in 16 cases. Pattern VEPs were generally well preserved, but showed a tendency to increase in latency and decrease in amplitude with age. These results confirm other reports that the retinopathy appears to be a progressive rod-cone dystrophy initially affecting mainly extramacular areas but involving the macula at later stages. Seven of 11 patients showed abnormalities of either optokinetic nystagmus, vestibulo-ocular reflex, or both. These eye-movement abnormalities have not been reported previously, and are further evidence of central nervous system involvement in this syndrome.

Nystagmus: neglected no longer ?

Nystagmus is an eye condition which has so far received comparatively little attention. This article discusses the nature and effects of the condition with particular reference to children. It emphasises the need for a wider knowledge of the disease and for further research into treatment and possible cures.

Eye movement and electrophysiological findings in an infant with hemispheric pathology

A visually unresponsive infant had a normal ophthalmological examination. Eye-movement studies using electro-oculography revealed asymmetrical binocular smooth pursuit, binocular optokinetic nystagmus and vestibulo-ocular reflex. Electrophysiological testing showed markedly asymmetrical occipital flash and pattern visual evoked potentials. Both investigations suggested a posterior right-hemispheric problem, which was confirmed with cranial ultrasound. This case study illustrates the usefulness of non-invasive techniques in neuro-ophthalmological investigations of young children.