Clinical and ocular motor analysis of congenital nystagmus in infancy

Botulinum Toxin A Injection in Horizontal Nystagmus: Effect on the Frequency of the Oscillation on a Pediatric Population

PURPOSE

To evaluate the effect of botulinum toxin A injection on the frequency of horizontal nystagmus in children.

METHODS

This was a non-randomized before-and-after clinical trial evaluating a cohort of children with horizontal nystagmus before and after treatment with botulinum toxin A. The toxin was injected under general anesthesia with spontaneous ventilation without intubation using the Mendonça forceps and the effect was evaluated by analyzing the frequency of the oscillation in Hertz (Hz) on video registrations before and after treatment.

RESULTS

The current study found a statistically significant difference on the frequency of the nystagmus in children before and after the injection of botulinum toxin A, with the mean frequency decreasing from 1.55 ± 0.94 Hz before treatment to 1.04 ± 0.87 Hz at 1 month post-injection (P < .001) and to 1.27 ± 0.87 Hz at 6 months post-injection (P = .002). When comparing the data 1 and 6 months post-injection, this study found a significant increase (P = .001) in the frequency of the nystagmus.

CONCLUSIONS

The injection of botulinum toxin A is effective in reducing the frequency of oscillations in children with horizontal nystagmus both 1 and 6 months after the procedure, and can be used as a first-line, less invasive treatment aiming to decrease the frequency of oscillation. [J Pediatr Ophthalmol Strabismus. 20XX;X(X):XXX-XXX.].

Nystagmus in the B6(CG)Tyr(c-2J)/J Albino Mouse: A Functional and RNA-Seq Analysis

Purpose

Infantile nystagmus syndrome (INS) is a gaze-holding disorder characterized by conjugate, uncontrolled eye oscillations that can result in significant visual acuity loss. INS is often associated with albinism, but the mechanism is unclear. Albino mice have nystagmus; however, a pigmented mouse with a tyr mutation making it phenotypically albino, the B6(CG)-Tyr(c-2J)/J (B6 albino), had not been tested. We tested optokinetic response (OKR) in B6 albino and control mice. RNA-Seq was performed on extraocular muscles (EOM), tibialis anterior (TA) muscle, abducens (CN6), and oculomotor (CN3) neurons to uncover molecular differences that may contribute to nystagmus.

Methods

OKR was measured using an ISCAN system. RNA was isolated from four tissues to identify differentially expressed genes and validated with qPCR and immunohistochemistry. Ingenuity pathway analyses identified top biological pathways.

Results

All B6 albino mice tested had nystagmus. Differential RNA expression analysis showed 383 genes differentially expressed in EOM, 70 in CN3, 20 in CN6, and 639 in the TA. Two genes were differentially expressed in all four tissues: wdfy1 and nnt. Differences were validated by qPCR and immunostaining.

Conclusions

The tyr mutation in B6 albino mice, genotypically pigmented and phenotypically albino, is sufficient to result in spontaneous nystagmus. The two genes with decreased expression in the B6 albino tissues examined, wdfy1 and nnt, have been implicated in mitochondrial dysfunction and stem cell maintenance in other systems. Their function in extraocular muscle is unknown. These studies suggest that this mouse model of nystagmus may allow molecular identification of candidate nystagmus-related genes.

A new gene mutation in a family with idiopathic infantile nystagmus

Idiopathic infantile nystagmus (IIN) is an inherited disease, which can occur through a number of different inheritance patterns (autosomal dominant, recessive, or X-linked). The most common of these is X-linked inheritance with incomplete penetrance and variable expressivity, and can also be dominant or recessive. To date, only two mutations have been described: the first, affecting the FPR143 gene, which is associated with ocular albinism type I, and located on chromosome Xp22, and the second, affecting the FRMD7 gene located on chromosome X26-q27. To date, a causative gene on locus Xp11.3p11.4 has not yet been identified. The most common cause of IIN is due to mutations in the FRMD7 gene, located on chromosome Xq26. We present a case of a new mutation found in three siblings from a family with FRMD7-related infantile nystagmus, whose parents are consanguineously related in the first degree. A complex mutation has occurred in this family, which, to date, has not been previously reported in the scientific literature. The complex mutation consists of the presence of three consecutive 1 bp deletions in exon 12 (c.1248delT; 1299del C; and 1312delT), causing a secondary deletion (c. 1340–2145 + 214del), and resulting in a truncated protein. We also present a 7-year-old patient from a different family, with periodic alternating nystagmus, having no mutation in the FRMD7 gene, which we assume may be an example of non-FRMD7-related IIN. This patient does not have a family history of nystagmus.

Surgical interventions for infantile nystagmus syndrome

BACKGROUND

Infantile nystagmus syndrome (INS) is a type of eye movement disorder that can negatively impact vision. Currently, INS cannot be cured, but its effects can potentially be treated pharmacologically, optically, or surgically. This review focuses on the surgical interventions for INS. Despite the range of surgical interventions available, and currently applied in practice for the management of INS, there is no clear consensus, and no accepted clinical guidelines regarding the relative efficacy and safety of the various treatment options. A better understanding of these surgical options, along with their associated side effects, will assist clinicians in evidence-based decision-making in relation to the management of INS.

OBJECTIVES

To assess the efficacy and safety of surgical interventions for INS.

SEARCH METHODS

We searched CENTRAL, MEDLINE Ovid, Embase Ovid, ISRCTN registry, ClinicalTrials.gov, and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) to 3 July 2020, with no language restrictions.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) studying the efficacy and safety of surgical options for treating INS.

DATA COLLECTION AND ANALYSIS

Our prespecified outcome measures were the change from baseline in: binocular best-corrected distance visual acuity; head posture; amplitude, frequency, intensity, and foveation period durations of the nystagmus waveform; visual recognition times; quality of life and self-reported outcome measures; incidence of adverse effects with a probable causal link to treatment; and permanent adverse effects after surgery. Two review authors independently screened titles and abstracts and full-text articles, extracted data from eligible RCTs, and judged the risk of bias using the Cochrane tool. We reached consensus on any disagreements by discussion. We summarised the overall certainty of the evidence using the GRADE approach.

MAIN RESULTS

We only identified one eligible RCT (N = 10 participants), undertaken in India. This trial randomised participants to receive either a large retro-equatorial recession of the horizontal rectus muscle of 9 mm on the medial rectus and 12 mm on the lateral rectus, or a simple tenotomy and resuturing of the four horizontal rectus muscles. We did not identify any RCTs comparing a surgical intervention for INS relative to no treatment. In the single eligible RCT, both eyes of each participant received the same intervention. The participants' age and gender were not reported, nor was information on whether participants were idiopathic or had sensory disorders. The study only included participants with null in primary position and did not explicitly exclude those with congenital periodic alternating nystagmus. The study did not report funding source(s) or author declaration of interests. The evaluation period was six months. We judged this study at low risk for sequence generation and other sources of bias, but at high risk of bias for performance and detection bias. The risk of bias was unclear for selection bias, attrition bias, and reporting bias. There is very uncertain evidence about the effect of the interventions on visual acuity and change in amplitude, frequency, and intensity of the nystagmus waveform. We were unable to calculate relative effects due to lack of data. None of the participants in either intervention group reported adverse effects at six-month follow-up (very low-certainty evidence). There was no quantitative data reported for quality of life, although the study reported an improvement in quality of life after surgery in both intervention groups (very low-certainty evidence). Change in head posture, foveation period durations of the nystagmus waveform, visual recognition times, and permanent adverse effects after surgery were not reported in the included study. We judged the certainty of the evidence, for both the primary and secondary efficacy outcomes, to be very low. Due to a lack of comprehensive reporting of adverse events, there was also very low-certainty of the safety profile of the evaluated surgical interventions in this population. As such, we are very uncertain about the relative efficacy and safety of these interventions for the surgical management of INS.

AUTHORS' CONCLUSIONS

This systematic review identified minimal high-quality evidence relating to the efficacy and safety of surgical interventions for INS. The limited availability of evidence must be considered by clinicians when treating INS, particularly given these procedures are irreversible and often performed on children. More high-quality RCTs are needed to better understand the efficacy and safety profile of surgical interventions for INS. This will assist clinicians, people with INS, and their parents or caregivers to make evidence-based treatment decisions.

Homozygous stop mutation in AHR causes autosomal recessive foveal hypoplasia and infantile nystagmus

Herein we present a consanguineous family with three children affected by foveal hypoplasia with infantile nystagmus, following an autosomal recessive mode of inheritance. The patients showed normal electroretinography responses, no signs of albinism, and no anterior segment or brain abnormalities. Upon whole exome sequencing, we identified a homozygous mutation (c.1861C>T;p.Q621*) in the aryl hydrocarbon receptor (AHR) gene that perfectly co-segregated with the disease in the larger family. AHR is a ligand-activated transcription factor that has been intensively studied in xenobiotic-induced toxicity. Further, it has been shown to play a physiological role under normal cellular conditions, such as in immunity, inflammatory response and neurogenesis. Notably, knockout of the Ahr gene in mouse impairs optic nerve myelin sheath formation and results in oculomotor deficits sharing many features with our patients: the eye movement disorder in Ahr-/- mice appears early in development and presents as conjugate horizontal pendular nystagmus. We therefore propose AHR to be a novel disease gene for a new, recessively inherited disorder in humans, characterized by infantile nystagmus and foveal hypoplasia.

Reading Performance and Compensatory Head Posture in Infantile Nystagmus after Null Zone Training

This study aimed to assess the visual function, reading performance, and compensatory head posture (CHP) in schoolchildren with infantile nystagmus. A total of 18 participants aged between 13 to 18 years old were divided into spectacle (n = 9) and null zone group (n = 9) based on their visual acuity. Visual acuity (LogMAR), contrast sensitivity (Pelli–Robson), reading time and rate (Tobii TX300), and CHP were measured pre and post null zone reading training. Participants in the null zone group received 10 sessions of training (5 weeks). Visual acuity and contrast sensitivity of participants in the spectacle and null zone groups were not significantly different pre and post training. Reading performance, i.e., reading time (z = −1.36; p = 0.173) and reading rate (z = −0.06; p = 0.953), of participants in the spectacle group was not significantly different after 5 weeks. Reading time (z = −2.55; p = 0.011) and reading rate (z = −2.07; p = 0.038 of participants in the null zone group showed significant improvement post training. After 5 weeks, CHP improved in six out of the nine participants (66.7%) of the null zone group and was unchanged in all participants in the spectacle group. Null zone reading training could benefit children with infantile nystagmus in improving reading performance and compensatory head posture.

Reliability and Validity of Gaze-Dependent Functional Vision Space: A Novel Metric Quantifying Visual Function in Infantile Nystagmus Syndrome

Purpose

This study presents test–retest reliability of optotype visual acuity (OVA) across 60° of horizontal gaze position in patients with infantile nystagmus syndrome (INS). Also, the validity of the metric gaze-dependent functional vision space (GDFVS) is shown in patients with INS.

Methods

In experiment 1, OVA was measured twice in seven horizontal gaze positions from 30° left to right in 10° steps in 20 subjects with INS and 14 without INS. Test–retest reliability was assessed using intraclass correlation coefficient (ICC) in each gaze. OVA area under the curve (AUC) was calculated with horizontal eye position on the x-axis, and logMAR visual acuity on the y-axis and then converted to GDFVS. In experiment 2, validity of GDFVS was determined over 40° horizontal gaze by applying the 95% limits of agreement from experiment 1 to pre- and post-treatment GDFVS values from 85 patients with INS.

Results

In experiment 1, test–retest reliability for OVA was high (ICC ≥ 0.88) as the difference in test–retest was on average less than 0.1 logMAR in each gaze position. In experiment 2, as a group, INS subjects had a significant increase (P < 0.001) in the size of their GDFVS that exceeded the 95% limits of agreement found during test–retest.

Conclusions

OVA is a reliable measure in INS patients across 60° of horizontal gaze position. GDFVS is a valid clinical method to be used to quantify OVA as a function of eye position in INS patients. This method captures the dynamic nature of OVA in INS patients and may be a valuable measure to quantify visual function patients with INS, particularly in quantifying change as part of clinical studies.

Beat-to-beat control of human optokinetic nystagmus slow phase durations

This study provides the first clear evidence that the generation of optokinetic nystagmus fast phases (FPs) is a decision process that is influenced by performance of a concurrent disjunctive reaction time task (DRT). Ten subjects performed an auditory DRT during constant velocity optokinetic stimulation. Eye movements were measured in three dimensions with a magnetic search coil. Slow phase (SP) durations were defined as the interval between FPs. There were three main findings. Firstly, human optokinetic nystagmus SP durations are consistent with a model of a Gaussian basic interval generator (a type of biological clock), such that FPs can be triggered randomly at the end of a clock cycle (mean duration: 200-250 ms). Kolmogorov-Smirnov tests could not reject the modeled cumulative distribution for any data trials. Secondly, the FP need not be triggered at the end of a clock cycle, so that individual SP durations represent single or multiple clock cycles. Thirdly, the probability of generating a FP at the end of each interval generator cycle decreases significantly during performance of a DRT. These findings indicate that the alternation between SPs and FPs of optokinetic nystagmus is not purely reflexive. Rather, the triggering of the next FP is postponed more frequently if a recently presented DRT trial is pending action when the timing cycle expires. Hence, optokinetic nystagmus FPs show dual-task interference in a manner usually attributed to voluntary movements, including saccades.

NEW & NOTEWORTHY

This study provides the first clear evidence that the generation of optokinetic nystagmus (OKN) fast phases is a decision process that is influenced by performance of a concurrent disjunctive reaction time task (DRT). The slow phase (SP) durations are consistent with a Gaussian basic interval generator and multiple interval SP durations occur more frequently in the presence of the DRT. Hence, OKN shows dual-task interference in a manner observed in voluntary movements, such as saccades.

Infantile nystagmus syndrome: clinical characteristics, current theories of pathogenesis, diagnosis, and management

Infantile nystagmus syndrome (INS) is an important clinical diagnosis because it is a common presenting sign of many ocular, neurologic, and systemic diseases. Although INS has been studied for more than a century, its diagnosis and treatment remains a challenge to clinicians because of its varied manifestations and multiple associations, and its pathogenesis continues to rouse considerable scientific debate. Fueled by these challenges, recent basic research and clinical investigations have provided new insights into INS. New genetic discoveries and technological advances in ocular imaging have refined our understanding of INS subtypes and offer new diagnostic possibilities. Unexpected surgical outcomes have led to new understanding of its pathogenesis based on novel hypothesized pathways of ocular motor control. Comparative studies on nonhuman visual systems have also informed models of the neural substrate of INS in humans. This review brings together the classic profile of this disorder with recent research to provide an update on the clinical features of INS, an overview of the current theories on how and why INS develops, and a practical approach to the diagnosis and management of INS.

Myectomy of the Extraocular Muscles Without Reattachment as a Surgical Treatment for Horizontal Nystagmus

PURPOSE

To report the comparative clinical findings for two nystagmus procedures in two consecutive case series: the Sinskey anterior extirpation procedure (SAEP) and a modification, myectomy without reattachment (MWR).

METHODS

Twenty consecutive patients underwent the SAEP and 19 underwent MWR. The SAEP is a snare-assisted unmeasured deep myectomy, whereas MWR is a measured myectomy at posterior Tenon's fascia. All patients underwent comprehensive ophthalmologic and orthoptic examination with infrared videonystagmography. Binocular best corrected visual acuity, nystagmus amplitude, alignment, and versions outcomes were measured.

RESULTS

The highest percentage of patients experiencing two or more lines of improvement in distance and near acuity was in the SAEP group, who were younger than 10 years and had no ocular comorbidity (100%). Distance and near acuity improved at least one line in 71% and 86% of patients in the SAEP group and 72% and 61% in the MWR group, respectively. In both groups, patients younger than 10 years had the best acuity gains. Average nystagmus amplitude was reduced 76.3% (SAEP) and 68% (MWR). Horizontal versions were more compromised in the SAEP group and one patient experienced intraoperative orbital bleeding. Patients requiring reoperation for strabismus numbered 5 of 20 (20%) in the SAEP and 3 of 19 (16%) in the MWR groups.

CONCLUSIONS

Similar to SAEP, the MWR procedure reduces nystagmus amplitudes and improves visual acuity but with less limitation of versions, risk of intraoperative bleeding, and risk of postoperative strabismus. Data suggest that early surgery (for patients younger than 10 years) can have a greater beneficial effect on postoperative visual acuity. [J Pediatr Ophthalmol Strabismus. 2016;53(3):156-166.].

The relationship between visual orienting responses and clinical characteristics in children attending special education for the visually impaired

We recently introduced a method based on quantification of orienting responses toward visual stimuli to assess the quality of visual information processing in children. In the present study, we examined the relationship between orienting responses and factors that are associated with visual processing impairments in current clinical practice. Response time and fixation quality to visual features such as form, contrast, motion, and color stimuli were assessed in 104 children from 1 to 12 years attending special education for the visually impaired. Using regression analysis, we investigated whether these parameters were affected by clinical characteristics of children. Response times significantly depended on stimulus type. Responses to high-contrast cartoons were significantly slower in children with a clinical diagnosis of cerebral visual impairment. Fixation quality was significantly affected by visual acuity and nystagmus. The results suggest that the quantitative measurement of orienting responses is strongly related to cerebral visual impairment in children.

Topical brinzolamide (Azopt) versus placebo in the treatment of infantile nystagmus syndrome (INS)

PURPOSE

To test the hypothesis that the topical carbonic anhydrase inhibitor brinzolamide (Azopt) has beneficial effects versus placebo on measures of nystagmus and visual acuity in adult subjects with infantile nystagmus syndrome (INS).

DESIGN

Prospective, cross-over, double masked clinical trial.

METHODS

SETTING

Single centre.

STUDY POPULATION

Five subjects ≥18 years old with typical INS and best-binocular visual acuity in their primary position null zone ETDRS 55 letters to 85 letters (20/200 to 20/50) and had no previous treatment for nystagmus.

INTERVENTION

In a randomised order, each subject received one drop of Azopt or placebo in both eyes three times a day separated by a washout period of at least a week followed by Azopt or placebo in both eyes three times a day; thus each subject got the drug and placebo, each acting as his or her own control.

OUTCOME MEASURES

The nystagmus acuity function and INS waveforms obtained from eye movement recordings, binocular optotype visual acuity, using the ETDRS protocol analysed individually and as a group before and after Azopt and placebo.

RESULTS

Versus placebo and baseline measures, topical Azopt significantly improved; INS waveform characteristics in the primary position null zone, group mean values of the nystagmus acuity function across gaze (p<0.01) and group mean ETDRS binocular letter visual acuity (p<0.05). There was a predictable decrease in intraocular pressure (IOP) without any systemic or ocular adverse events.

CONCLUSIONS

Although a prospective large-scale clinical trial is needed to prove effectiveness, an eye-drop-based therapy for INS may emerge as a viable addition to optical, surgical, behavioural and systemic drug therapies for INS.

TRIAL REGISTRATION NUMBER

NCT01312402.

Nystagmus in childhood

Nystagmus is an involuntary rhythmic oscillation of the eyes, which leads to reduced visual acuity due to the excessive motion of images on the retina. Nystagmus can be grouped into infantile nystagmus (IN), which usually appears in the first 3-6 months of life, and acquired nystagmus (AN), which appears later. IN can be idiopathic or associated to albinism, retinal disease, low vision, or visual deprivation in early life, for example due to congenital cataracts, optic nerve hypoplasia, and retinal dystrophies, or it can be part of neurological syndromes and neurologic diseases. It is important to differentiate between infantile and acquired nystagmus. This can be achieved by considering not only the time of onset of the nystagmus, but also the waveform characteristics of the nystagmus. Neurological disease should be suspected when the nystagmus is asymmetrical or unilateral. Electrophysiology, laboratory tests, neurological, and imaging work-up may be necessary, in order to exclude any underlying ocular or systemic pathology in a child with nystagmus. Furthermore, the recent introduction of hand-held spectral domain optical coherence tomography (HH SD-OCT) provides detailed assessment of foveal structure in several pediatric eye conditions associated with nystagmus and it can been used to determine the underlying cause of infantile nystagmus. Additionally, the development of novel methods to record eye movements can help to obtain more detailed information and assist the diagnosis. Recent advances in the field of genetics have identified the FRMD7 gene as the major cause of hereditary X-linked nystagmus, which will possibly guide research towards gene therapy in the future. Treatment options for nystagmus involve pharmacological and surgical interventions. Clinically proven pharmacological treatments for nystagmus, such as gabapentin and memantine, are now beginning to emerge. In cases of obvious head posture, eye muscle surgery can be performed to shift the null zone of the nystagmus into the primary position, and also to alleviate neck problems that can arise due to an abnormal head posture.

Long-term results of four horizontal rectus muscle recession in nystagmus treatment

PURPOSE

To report the long-term results of four horizontal rectus muscle recessions that were performed for infantile nystagmus syndrome treatment.

METHODS

In this case series, patients with infantile nystagmus syndrome who had four horizontal muscle recessions previously were recruited and ophthalmological examination and electronystagmography recordings were performed. Objectively, amplitude and frequency of nystagmus were measured from the recordings and the intensity was calculated. Visual acuity, stereopsis, and alignment were evaluated and compared with the preoperative and postoperative values.

RESULTS

The records of the 12 patients who had four horizontal rectus muscle recession surgery were evaluated and six patients (5 male, 1 female) who had regular follow-ups were included in this study. Mean follow-up was 14.17 ± 0.41 years (minimum 14 years, maximum 15 years) and mean age of patients at the last visit was 22 years (20-28 years). On subjective evaluation, two-thirds (4/6) of the patients were satisfied with the surgical results and had the impression that after surgery, nystagmus decreased in intensity and head posture improved. On objective evaluation, visual acuity was found to be the same, however, stereopsis improved (preoperatively and postoperatively median stereopsis was 600 sec arc vs 200 sec arc final). The decrease in nystagmus amplitude and frequency was still maintained.

CONCLUSIONS

Nystagmus surgery on four horizontal rectus muscles has positive effects on binocular function and nystagmus parameters in the long-term follow-up. As we could not treat the primary pathology, the visual acuity was about the same but the decrease in nystagmus amplitude and frequency was still maintained with better stereopsis, and patient satisfaction.

Infantile and acquired nystagmus in childhood

Nystagmus is an involuntary, periodic eye movement caused by a slow drift of fixation which is followed by a fast refixation saccade (jerk nystagmus) or a slow movement back to fixation (pendular nystagmus). In childhood most cases are benign forms of nystagmus: idiopathic infantile, ocular or latent nystagmus. They arise at the age of 3 months, without oscillopsia and show the absence of the physiologic opto-kinetic nystagmus. A full ophthalmologic evaluation is all that is needed in most cases: albinism, macular or optic nerve hypoplasia and congenital retinal dystrophies are the most common forms of ocular nystagmus. Idiopathic infantile nystagmus can be hereditary, the most common and best analyzed form being a mutation of the FRMD7 gene on chromosome Xq26.2. The mutation shows a mild genotype-phenotype correlation. In all female carriers the opto-kinetic nystagmus is absent and half had mild nystagmus. Latent nystagmus is part of the infantile esotropia syndrome and shows the unique feature of change of direction when the fixing eye changes: it is always beating to the side of the fixing eye. There is no cure for infantile nystagmus but therapeutic options include magnifying visual aids or eye muscle surgery at the age of 6-8 y in patients with head turn. Less than 20% of childhood nystagmus are acquired and need further neurological and imaging work-up. Alarming signs and symptoms are: onset after the age of 4 months, oscillopsia, dissociated (asymmetric) nystagmus, preserved opto-kinetic nystagmus, afferent pupillary defect, papilloedema and neurological symptoms like vertigo and nausea. The most common cause is due to pathology of the anterior optic pathway (e.g. optic nerve gliomas). It shows the same clinical feature of dissociated nystagmus as spasmus nutans but has a higher frequency as in INO. Other forms of acquired nystagmus are due to brainstem, cerebellar or metabolic diseases.

[Use of botulinum toxin in a patient with pendular congenital nystagmus]

CASE REPORT

We report the case of a 5 month-old male diagnosed with congenital nystagmus and oculocutaneous albinism. The initial examination showed pendular horizontal nystagmus with high amplitude and without blocking position or foveal fixation periods. A 2.5 IU injection of botulinum toxin was administered in the horizontal rectus muscles of both eyes in two sessions separated by 6 weeks. This led to a decrease in amplitude of nystagmus and early development of binocular visual acuity of 4.8cycles/cm.

CONCLUSION

Faced with diagnosis of horizontal nystagmus in the early stages of development, and in order to avoid periods of foveal fixation, the use of botulinum toxin leads to a temporary reduction in its amplitude and an improvement in visual acuity with low complication rates. Given the possibility of spontaneous improvement described in these patients, studies are needed with longer follow-up to establish the advantage of long term treatment.

Intracranial pathology in young children with apparently isolated nystagmus

PURPOSE

To assess the incidence of intracranial pathology in young children who had brain magnetic resonance imaging (MRI) to investigate apparently isolated nystagmus noted within the first few years of life.

METHODS

Retrospective institutional review of such children (up to 5 years old).

RESULTS

Twenty-six patients (17 boys, 9 girls) were identified. Nystagmus was clinically bilateral in 22 (85%) and unilateral in 4 (15%). Seventeen cases (65%) were described as horizontal pendular nystagmus, 5 (19%) as horizontal jerk nystagmus, 2 (8%) as vertical pendular nystagmus, and 1 each as downbeat nystagmus and torsional nystagmus (8%). Three of the 26 patients (12%) had significant MRI findings and all three had temporal optic nerve head pallor noted during clinical examination. Nystagmus was horizontal pendular in two patients and rotary in the third.

CONCLUSION

The optic nerve head should be carefully assessed for signs of pallor in young children with nystagmus and, if present, brain MRI should be performed. Otherwise, isolated early childhood nystagmus is unlikely to be associated with intracranial pathology. Clinical description of nystagmus did not predict intracranial pathology in this cohort.

Comparison of infantile nystagmus syndrome in achiasmatic zebrafish and humans

Infantile nystagmus syndrome (INS; formerly called congenital nystagmus) is an ocular motor disorder characterized by several typical nystagmus waveforms. To date, restrictions inherent to human research and the absence of a handy animal model have impeded efforts to identify the underlying mechanism of INS. Displaying INS-like spontaneous eye oscillations, achiasmatic zebrafish belladonna (bel) mutants may provide new insights into the mystery of INS. In this study, we demonstrate that these spontaneous eye oscillations match the diagnostic waveforms of INS. As a result, zebrafish bel mutants can be used as an animal model for the study of INS. In zebrafish bel mutants, visual pathway abnormalities may contribute to the spontaneous nystagmus via an inverted signal to the pretectal area. We hypothesized that human INS may also be linked to visual pathway abnormalities (possibly underdiagnosed in INS patients) in a similar way.

Nystagmus and saccadic intrusions

We review current concepts of nystagmus and saccadic oscillations, applying a pathophysiological approach. We begin by discussing how nystagmus may arise when the mechanisms that normally hold gaze steady are impaired. We then describe the clinical and laboratory evaluation of patients with ocular oscillations. Next, we systematically review the features of nystagmus arising from peripheral and central vestibular disorders, nystagmus due to an abnormal gaze-holding mechanism (neural integrator), and nystagmus occurring when vision is compromised. We then discuss forms of nystagmus for which the pathogenesis is not well understood, including acquired pendular nystagmus and congenital forms of nystagmus. We then summarize the spectrum of saccadic disorders that disrupt steady gaze, from intrusions to flutter and opsoclonus. Finally, we review current treatment options for nystagmus and saccadic oscillations, including drugs, surgery, and optical methods. Examples of each type of nystagmus are provided in the form of figures.

Eye muscle surgery for infantile nystagmus syndrome in the first two years of life

Purpose:

To report visual and elctrophysioloigcal effects of eye muscle surgery in young patients with infantile nystagmus syndrome (INS).

Methods:

Prospective, interventional case cohort of 19 patients aged under 24 months who were operated on for combinations of strabismus, an anomalous head posture, and nystagmus. All patients were followed at least nine months. Outcome measures, part of an institutionally approved study, included Teller acuity, head position, strabismic deviation, and eye movement recordings, from which waveform types and a nystagmus optimal foveation fraction (NOFF). Computerized parametric and nonparametric statistical analysis of data were perfomed using standard software on both individual and group data.

Results:

Age averaged 17.7 months (13.1-month follow-up). Thirteen (68%) patients had associated optic nerve or retinal disease. 42% had amblyopia, 68% had refractive errors. Group means in binocular Teller acuity (P < 0.05), strabismic deviation (P < 0.05), head posture (P < 0.001), and the NOFF measures (P < 0.01) from eye movement recordings improved in all patients. There was a change in null zone waveforms to more favorable jerk types. There were no reoperations or surgical complications.

Conclusions:

Surgery on the extraocular muscles in patients aged less than two years with INS results in improvements in multiple aspects of ocular motor and visual function.

Nystagmus in infancy and childhood

Involuntary occular oscillations in infancy and childhood can be understood, diagnosed, classified and treated as a result of modern electrophysiology and neuroanatomical knowledge.

Infantile aperiodic alternating nystagmus

BACKGROUND

This study identifies the clinical and ocular motility characteristics of the periodic and aperiodic forms of infantile alternating nystagmus (IAPAN) and establishes the range of electrophysiological and clinical characteristics while providing clues to its presence and pathophysiology.

METHODS

Seventy-eight patients with ocular oscillations consistent with IAPAN were reported. Outcome variables were: age, follow-up in months, vision, strabismus, other eye and systemic abnormalities, head position, periodicity, cycle and null period duration, foveation time, waveforms, and cycle symmetry.

RESULTS

Age range was 1 to 67 years, 50% had pure periodic and aperiodic forms, 46% had albinism, 26% had binocular acuity of 20/40 or greater, 72% had strabismus, 35% had amblyopia, 31% had other eye disease, 14% had systemic disease, 87% had an anomalous head posture, and 65% had binocular directional asymmetry. The periodic cycle averaged 224 seconds and the aperiodic cycle ranged from 2 to more than 300 seconds. One in three patients with strabismus and nystagmus periodicity had a static head posture.

CONCLUSION

Fifteen percent of the infantile nystagmus syndrome population had either the periodic or aperiodic form. A changing null period is often clinically missed because of long or irregular cycles, decreased acuity, associated strabismus, and either a nonexistent or inconsistent head posture. The changing null period is easier to recognize using eye movement recordings or if the non-preferred eye is occluded and the preferred eye is examined with the head straight and gaze in primary position for at least 5 to 7 minutes. The recognition of this variant has profound treatment implications.

Phenotypical characteristics of idiopathic infantile nystagmus with and without mutations in FRMD7

Idiopathic infantile nystagmus (IIN) consists of involuntary oscillations of the eyes. The familial form is most commonly X-linked. We recently found mutations in a novel gene FRMD7 (Xq26.2), which provided an opportunity to investigate a genetically defined and homogeneous group of patients with nystagmus. We compared clinical features and eye movement recordings of 90 subjects with mutation in the gene (FRMD7 group) to 48 subjects without mutations but with clinical IIN (non-FRMD7 group). Fifty-eight female obligate carriers of the mutation were also investigated. The median visual acuity (VA) was 0.2 logMAR (Snellen equivalent 6/9) in both groups and most patients had good stereopsis. The prevalence of strabismus was also similar (FRMD7: 7.8%, non-FRMD7: 10%). The presence of anomalous head posture (AHP) was significantly higher in the non-FRMD7 group (P < 0.0001). The amplitude of nystagmus was more strongly dependent on the direction of gaze in the FRMD7 group being lower at primary position (P < 0.0001), compared to non-FRMD7 group (P = 0.83). Pendular nystagmus waveforms were also more frequent in the FRMD7 group (P = 0.003). Fifty-three percent of the obligate female carriers of an FRMD7 mutation were clinically affected. The VA's in affected females were slightly better compared to affected males (P = 0.014). Subnormal optokinetic responses were found in a subgroup of obligate unaffected carriers, which may be interpreted as a sub-clinical manifestation. FRMD7 is a major cause of X-linked IIN. Most clinical and eye movement characteristics were similar in the FRMD7 group and non-FRMD7 group with most patients having good VA and stereopsis and low incidence of strabismus. Fewer patients in the FRMD7 group had AHPs, their amplitude of nystagmus being lower in primary position. Our findings are helpful in the clinical identification of IIN and genetic counselling of nystagmus patients.

Compensatory head posture and neck problems: is there an association? A cohort study of nystagmus patients

PURPOSE

The aims of this study were twofold: to investigate if a compensatory head posture due to nystagmus causes long-term neck problems or adversely effects quality of life and to survey ophthalmologists on their opinions and management of these patients.

METHODS

A case-controlled study was carried out to assess the range of neck movements in patients with compensatory head posture due to congenital nystagmus. Exclusion criteria included known neck problems, vertebrobasilar insufficiency, and age less than 16 years. Neck movements were assessed using an inclinometer. Quality of life and disability was assessed using the American Academy of Orthopaedic Surgeons' Cervical Spine Questionnaire. One hundred and fifty consultant ophthalmologists throughout the United Kingdom were surveyed via a postal questionnaire.

RESULTS

The range of motion in these patients (n=20) was limited when compared to matched controls especially for lateral flexion (P=0.001) and extension (P=0.003). However, despite limited movement, patients did not perceive a disability and there was no adverse effect on quality of life. In all 55% of ophthalmologists believed compensatory head posture due to nystagmus leads to long-term neck problems. About 46% had personal experience of patients with long-term neck problems due to nystagmus. Eighty-four per cent were influenced in their decision to operate by the presence of a head posture.

CONCLUSIONS

Significant restriction in neck movements exists in nystagmus patients with compensatory head posture, although this does not appear to adversely affect quality of life.

Clinical and electrophysiological effects of extraocular muscle surgery on patients with Infantile Nystagmus Syndrome (INS)

The purpose of this report is to summarize clinical and electrophysiological effects of extraocular muscle surgery in patients with INS. Our hypothesis is that surgery on the extraocular muscles of patients with INS changes their nystagmus resulting in improved vision and visual functions. All patients had all four virgin horizontal recti operated on, either for strabismus alone, nystagmus alone, for a head posture due to an eccentric null zone alone or for a head posture due to an eccentric null zone plus strabismus. All patients have been followed for at least 12 months. Subjective outcome measures include the pre- and post-operative binocular best optically corrected null zone acuity (NZA) in 75 patients and gaze dependent acuity (GDA) in 12 patients. Objective outcome measure included null zone width (NZW) in 75 patients. The results are summarized as follows: NZA increased .1 LogMar or greater in 75% with those patients <or=8 years significantly better. Subjective GDA and NZW measured from eye movement recordings showed persistent, significant increases. This report adds to the evidence that surgery on the extraocular muscles in patients with INS has independent neurological and visual results, from simply reposition the head, eye(s) or visual axis.

Effects of extraocular muscle surgery on 15 patients with oculo-cutaneous albinism (OCA) and infantile nystagmus syndrome (INS)

PURPOSE

The purpose of this report is to characterize the clinical and electrophysiological effects of extraocular muscle surgery in 15 patients with oculo-cutaneous albinism (OCA) and infantile nystagmus syndrome (INS). Our hypothesis is that surgery on the extraocular muscles of patients with OCA and INS changes their nystagmus and their visual function.

DESIGN

Interventional, prospective, cohort, noncomparative case series.

METHODS

All 15 patients had surgery on all four virgin horizontal recti; three for strabismus alone, three for nystagmus alone, five for an eccentric gaze null zone alone, and four for an eccentric gaze null zone plus strabismus. All patients have been followed for at least six months. All 15 patients had the subjective outcome measure of pre- and postoperative binocular best optically corrected acuity (BBOCA). Objective outcome measures included anomalous head posture (AHP) in nine patients, eye movement recording measures of expanded nystagmus acuity function (NAFX) in 10 patients, null zone position (NUZP) and null zone width (NUZW) in 10 patients, and foveation time (FOV) in nine patients.

RESULTS

The results are summarized as follows; BBOCA increased 0.1 LogMar or greater in 14 of 15 patients. In those operated on for an AHP with or without associated strabismus the AHP improved significantly (P < .01 for all). The NAFX, NUZP, NUZW, and FOV measured from eye movement recordings showed persistent, significant increases in all patients (P < .01 for all).

CONCLUSIONS

This report adds to the evidence that surgery on the extraocular muscles in patients with INS has independent neurologic and visual results.

Infantile-onset nystagmus

PURPOSE OF REVIEW

Recent studies on the various forms of infantile-onset nystagmus have advanced our understanding of these disorders. The previously described waveforms of infantile nystagmus syndrome (congenital nystagmus) may be identified in infants less than 7 months of age, including the more mature forms; the visual status of these patients may be directly correlated with their mean foveation times.

RECENT FINDINGS

Refractive errors in patients with infantile nystagmus syndrome do not follow the expected trend toward emmetropization during infancy and early childhood. A study on the torsional component of nystagmus present in most patients with infantile nystagmus syndrome found it to be generated centrally and not by peripheral or mechanical dynamics. Two psychophysical studies on patients with infantile nystagmus syndrome revealed significant differences compared with control subjects. Two different animal models imply that lack of normal visual motion during a critical period of development in infancy leads to infantile nystagmus syndrome. An electron microscopic study of the enthesis site-where the extraocular muscle tendon inserts onto the sclera-in normal individuals versus patients with infantile nystagmus syndrome revealed significant abnormalities in the latter. Significant demographic and socioeconomic differences were reported between patients with infantile nystagmus syndrome and those with spasmus nutans.

SUMMARY

New evidence supports a role for sympathomimetic modulation of infantile nystagmus syndrome. Novel surgical treatments for infantile nystagmus syndrome are also discussed.

Relationships between visual acuity and anomalous head posture in patients with congenital nystagmus

PURPOSE

To determine whether patients with congenital nystagmus and an anomalous head posture have better binocular visual acuity than such patients without an anomalous head posture.

PATIENTS AND METHODS

This was an observational case series of prospectively collected data for 125 patients with clinical and oculographically confirmed congenital nystagmus. Clinical data were tabulated using computer software. Statistical analyses compared binocular visual acuity with and without the presence of a clinically evident anomalous head posture and visual acuity with and without associated sensory disease.

RESULTS

The mean visual acuity was 20/42 (log of the minimal angle of resolution [MAR], 0.32) in patients with an anomalous head posture and 20/83 (logMAR, 0.62) in patients with no anomalous head posture (P < .001). Among patients with disease of the sensory system, those with an anomalous head posture had a mean visual acuity of 20/55 (logMAR, 0.44) and those without an anomalous head posture had a mean visual acuity of 20/108 (logMAR, 0.73; P < .001).

CONCLUSIONS

Visual acuity was found to be significantly better in patients with congenital nystagmus who had an anomalous head posture versus those without such a head posture. Our findings indicate that the presence of an anomalous head posture in a patient with congenital nystagmus correlates with good vision and thus may be considered a positive prognostic sign in a preverbal child.

Motor and sensory characteristics of infantile nystagmus

BACKGROUND/AIMS

Past studies have explored some of the associations between particular motor and sensory characteristics and specific categories of non-neurological infantile nystagmus. The purpose of this case study is to extend this body of work significantly by describing the trends and associations found in a database of 224 subjects who have undergone extensive clinical and psychophysical evaluations.

METHODS

The records of 224 subjects with infantile nystagmus were examined, where 62% were idiopaths, 28% albinos, and 10% exhibited ocular anomalies. Recorded variables included age, mode of inheritance, birth history, nystagmus presentation, direction of the nystagmus, waveform types, spatial and temporal null zones, head postures and nodding, convergence, foveation, ocular alignment, refractive error, visual acuity, stereoacuity, and oscillopsia.

RESULTS

The age distribution of the 224 patients was between 1 month and 71 years, with the mean age and mode being 23 (SD 16) years and 16-20 years respectively. By far the most common pattern of inheritance was found to be autosomal dominant (n = 40), with the nystagmus being observed by the age of 6 months in 87% of the sample (n = 128). 139 (62%) of the 224 subjects were classified as idiopaths, 63 (28%) as albinos, and 22 (10%) exhibited ocular anomalies. Conjugate uniplanar horizontal oscillations were found in 174 (77.7%) of the sample. 32 (14.3%) had a torsional component to their nystagmus. 182 (81.2%) were classed as congenital nystagmus (CN), 32 (14.3%) as manifest latent nystagmus (MLN), and 10 (4.5%) as a CN/MLN hybrid. Neither CN nor MLN waveforms were related to any of the three subject groups (idiopaths, albinos, and ocular anomalies) MLN was found in idiopaths and albinos, but most frequently in the ocular anomaly group. The most common oscillation was a horizontal jerk with extended foveation (n = 49; 27%). The amplitudes and frequencies of the nystagmus ranged between 0.3-15.7 degrees and 0.5-8 Hz, respectively. Periodic alternating nystagmus is commonly found in albinos. Albino subjects did not show a statistically significantly higher nystagmus intensity when compared with the idiopaths (p>0.01). 105 of 143 subjects (73%) had spatial nulls within plus or minus 10 degrees of the primary position although 98 subjects (69%) employed a compensatory head posture. Subjects with spatial null zones at or beyond plus or minus 20 degrees always adopted constant head postures. Head nodding was found in 38 subjects (27% of the sample). Horizontal tropias were very common (133 out of 213; 62.4%) and all but one of the 32 subjects with MLN exhibited a squint. Adult visual acuity is strongly related to the duration and accuracy of the foveation period. Visual acuity and stereoacuity were significantly better (p<0.01) in the idiopaths compared to the albino and ocular anomaly groups. 66 subjects out of a sample of 168 (39%) indicated that they had experienced oscillopsia at some time.

CONCLUSIONS

There are strong ocular motor and sensory patterns and associations that can help define an infantile nystagmus. These include the nystagmus being bilateral, conjugate, horizontal uniplanar, and having an accelerating slow phase (that is, CN). Decelerating slow phases (that is, MLN) are frequently associated with strabismus and early form deprivation. Waveform shape (CN or MLN) is not pathognomonic of any of the three subject groups (idiopaths, albinos, or ocular anomalies). There is no one single stand alone ocular motor characteristic that can differentiate a benign form of infantile nystagmus (CN, MLN) from a neurological one. Rather, the clinician must consider a host of clinical features.

Evaluation of vestibular function in young children

Together, these tests provide a full evaluation of vestibular function in infants and small children. If attention is paid to creating the appropriate testing environment, and interpretation of the tests takes into account the unique properties of the responses of infants and young children, this testing can provide a useful adjunct to audiometric evaluation in young children.

Clinical and ocular motor analysis of the infantile nystagmus syndrome in the first 6 months of life

BACKGROUND/AIMS

The infantile nystagmus syndrome (INS) usually begins in infancy and may or may not be associated with visual sensory system abnormalities. Little is known about its specific waveforms in the first 6 months of life or their relation to the developing visual system. This study identifies the clinical and ocular motility characteristics of the INS and establishes the range of waveforms present in the first 6 months of life.

METHODS

27 infants with involuntary ocular oscillations typical of INS are included in this analysis. They were evaluated both clinically and with motility recordings. Eye movement analysis was performed off line from computer analysis of digitised data. Variables analysed included age, sex, vision, ocular abnormalities, head position, and null zone, neutral zone characteristics, symmetry, conjugacy, waveforms, frequencies, and foveation times.

RESULTS

Ages ranged from 3 to 6.5 months (average 4.9 months). 15 patients (56%) had abnormal vision for age, nine (33%) had strabismus, five (19%) had an anomalous head posture, 13 (48%) had oculographic null and neutral positions, nine (33%) had binocular asymmetry, and only two showed consistent dysconjugacy. Average binocular frequency was 3.3 Hz, monocular frequency 6.6 Hz. Average foveation periods were longer and more "jerk" wave forms were observed in those patients with normal vision.

CONCLUSIONS

Common clinical characteristics and eye movement waveforms of INS begin in the first few months of infancy and waveform analysis at this time may help with both diagnosis and visual status.

Onset of oscillopsia after visual maturation in patients with congenital nystagmus

PURPOSE

To describe the clinical and oculographic characteristics of a cohort of five patients with congenital nystagmus (CN) and late-onset oscillopsia caused by a coincidental decline in other visual and/or ocular motor functions.

DESIGN

Retrospective, observational, case series.

PARTICIPANTS

Five visually mature patients with CN and recent-onset oscillopsia were evaluated clinically and with motility recordings.

INTERVENTION

Eye movement analysis was performed off-line by computer analysis of digitized data. Nystagmus was analyzed for null-zone characteristics, waveforms, frequency, amplitudes, and slow-phase drift velocity during foveation. Surgical and medical treatment of associated ocular conditions in four of five patients.

MAIN OUTCOME MEASURES

Presence of symptomatic oscillopsia and average time during foveation periods of slow-phase drift velocity less than 10 degrees /second.

RESULTS

One of the five patients had associated rod-cone dystrophy, and another had recurrence of childhood head posturing with return of an eccentric null zone. The remaining three patients had decompensated strabismus associated with their oscillopsia. All five patients complained of oscillopsia in primary position that was relieved in the four who received treatment. Treatment included prismatic correction in one patient and surgery in three. Recordings in primary position after treatment showed increased duration during foveation periods of slow-phase drift velocity less than 10 degrees /second and an overall decreased intensity (amplitude/frequency) of the nystagmus.

CONCLUSIONS

Symptomatic oscillopsia in patients with CN is unusual. This visually disturbing symptom can be precipitated by new or changing associated visual sensory conditions (e.g., decompensating strabismus, retinal degeneration). If the associated conditions can be treated, then accompanying oscillopsia may be relieved.

Nystagmus

Advances in understanding the organization of the ocular motor system, including its anatomy and pharmacology, have provided new insights into the pathogenesis of various forms of nystagmus. The discoveries of fibromuscular pulleys that govern the pulling directions of the extraocular muscles has provided a new conceptual framework to account for the different axes of rotation of vestibular and other types of movements that may contribute to nystagmus. Theoretical and experimental evidence has suggested that acquired pendular nystagmus, which is commonly due to multiple sclerosis, arises from the neural network that normally guarantees steady gaze by integrating premotor signals. Pharmacologic inactivation studies have implicated both gamma-aminobutyric acid (GABA) and glutamate as important transmitters in the neural integrator and suggested new drug therapies. New electro-optic devices may eventually prove to be effective treatment for the visual symptoms cause by acquired nystagmus. The demonstration of proprioceptive mechanisms in the distal extraocular muscles has provided a rationale for new operative treatments for congenital nystagmus.

Examination and refractive management of patients with nystagmus

Patients with nystagmus present unique challenges to the ophthalmologist. These patients can be difficult to examine and refract. Treatment options to improve vision or reduce disturbing visual symptoms are limited, which is disappointing to the patient and frustrating to the clinician. This paper will provide the clinician with one method of clinically organizing nystagmus, describe the patients who may benefit from optical treatments, and discuss the methodology used in their implementation. Techniques that will be discussed include patient examination and objective and subjective refraction. Optical treatments discussed include spectacles, prisms, contact lenses, and retinal image stabilization.

Nystagmus

This report reviews the recent contributions to the field of pathologic nystagmus. The classification and nomenclature of nystagmus with onset in infancy is controversial. Because there are differences in nystagmus forms between patients with idiopathic nystagmus and those with nystagmus associated with afferent sensory defects, a distinction between these two nystagmus types is proposed. The distinctions are also helpful for clinicians, because these separate entities imply different diagnostic evaluations and visual prognosis. Recent studies have confirmed that periodic alternating nystagmus is detected more easily if the patient is evaluated for a longer time period and occurs more commonly than previously thought. Psychophysical investigations indicate that extraretinal signals play an important role in suppression of oscillopsia in infantile nystagmus. Genetic analysis recently has allowed identification of genes of X-linked idiopathic nystagmus and achromatopsia.

Electroretinography is necessary for spasmus nutans diagnosis

The purpose of the present study was to determine whether that which clinically appeared to be spasmus nutans could actually represent retinal sensory deficits diagnosable by electroretinography. Eight patients clinically thought to have spasmus nutans underwent electroretinography according to international standards. Five had normal electroretinograms and represented cases of true spasmus nutans. Three patients had abnormal electroretinograms, indicating that they did not have spasmus nutans. The clinical findings used to diagnose spasmus nutans can be simulated by retinal dystrophies. A normal electroretinogram is needed to confirm the diagnosis of spasmus nutans.

Eye-movement recordings in the evaluation of ophthalmologic and neurologic disorders

This review focuses on the use of quantitative eye-movement recordings in the diagnosis of ophthalmologic and neurologic disorders and in the investigation of the pathophysiologic mechanisms of and possible treatments for these disorders. Recently developed methods for measuring eye movements about all three axes of rotation (horizontal, vertical, and torsion) are emphasized. These techniques are providing important insights into the basic physiology of eye-movement control and into the mechanisms of ocular motor disturbances in which torsion plays a significant role.