'Congenital' nystagmus may hide various ophthalmic diagnoses

Infantile nystagmus without overt eye abnormality: Early features and neuro-ophthalmological diagnosis

AIM

To analyse the neuro-ophthalmological data of children referred for further work-up of infantile nystagmus where ophthalmological evaluation had not achieved a diagnosis.

METHOD

We retrospectively reviewed medical records of patients presenting with infantile nystagmus at our institution between 2007 and 2019. Inclusion criteria were onset before 6 months of age, availability of complete ophthalmic examination, visual electrophysiological tests, and neurological examination. Children with a previous definite ophthalmological diagnosis at onset and those with uncertain nystagmus onset age were not recruited.

RESULTS

Out of 142 infants (mean age at nystagmus onset 3.6 mo, SD 1.7, range 0-6 mo; 56 females, 86 males), 23% had neurological nystagmus, 7% mixed neurological and sensory nystagmus, 48% sensory defect, and 22% idiopathic infantile nystagmus. The neurological diagnoses were inborn errors of metabolism, white matter genetic disorders, and brain malformations. The prevalent diagnosis in the sensory defect subgroup was retinal dystrophy.

INTERPRETATION

Infantile nystagmus without diagnostic ocular findings may be due to neurological, retinal, and optic nerve disorders or be a benign idiopathic condition. In infants with and without neurological abnormalities, the search for a sensory defect should include visual electrophysiology performed early in the diagnostic pathway.

WHAT THIS PAPER ADDS

Infantile nystagmus without diagnostic ophthalmological signs has an underlying neurological cause in 30% of cases. Neurological diagnoses include congenital brain malformations, and metabolic and genetic disorders. Sensory defects are part of systemic neurological disorders in 23% of infants. Electrophysiology is useful when ophthalmological examination is uninformative.

Normal and abnormal foveal development

Normal foveal development begins in utero at midgestation with centrifugal displacement of inner retinal layers (IRLs) from the location of the incipient fovea. The outer retinal changes such as increase in cone cell bodies, cone elongation and packing mainly occur after birth and continue until 13 years of age. The maturity of the fovea can be assessed invivo using optical coherence tomography, which in normal development would show a well-developed foveal pit, extrusion of IRLs, thickened outer nuclear layer and long outer segments. Developmental abnormalities of various degrees can result in foveal hypoplasia (FH). This is a characteristic feature for example in albinism, aniridia, prematurity, foveal hypoplasia with optic nerve decussation defects with or without anterior segment dysgenesis without albinism (FHONDA) and optic nerve hypoplasia. In achromatopsia, there is disruption of the outer retinal layers with atypical FH. Similarly, in retinal dystrophies, there is abnormal lamination of the IRLs sometimes with persistent IRLs. Morphology of FH provides clues to diagnoses, and grading correlates to visual acuity. The outer segment thickness is a surrogate marker for cone density and in foveal hypoplasia this correlates strongly with visual acuity. In preverbal children grading FH can help predict future visual acuity.

Prevalence and causes of infantile nystagmus in a large population-based Danish cohort

PURPOSE

The aim of this study was to provide a population-based estimate on the prevalence of infantile nystagmus and to describe the causes in the Capital Region of Denmark.

METHODS

Review of medical records of children with infantile nystagmus born in the period 1 January 2010 through 31 December 2017 and living in the Capital Region of Denmark. We used birth registry data from Statistics Denmark and the National Danish Birth Registry to calculate the prevalence of nystagmus in children born at term and prematurely.

RESULTS

A total of 103 patients (52 males/51 females) with infantile nystagmus were included. The overall prevalence of infantile nystagmus was 6.1 per 10 000 live births. It was higher in premature children (28.4/10 000 live births) than children born at term (4.4/10 000), p < 0.0001, and highest in children born extremely preterm, (97.3/10 000). The most common cause of infantile nystagmus was ocular disease (44%) followed by idiopathic nystagmus (32%), neurological disorders and genetic syndromes (20%) and prematurity without retinopathy of prematurity as the only cause (4%).

CONCLUSIONS

In this study, we provide the prevalence of infantile nystagmus based on national medical records in which all residents are accounted for. Our findings show a prevalence of 6.1 per 10 000 live births but six times higher among children born preterm than born at term. Ocular disease was the leading cause of infantile nystagmus with albinism and ocular malformations as the most frequent. In 1/3 of patients, no cause could be identified.

Nystagmus and optical coherence tomography findings in CNGB3-associated achromatopsia

PURPOSE

To describe the nystagmus characteristics of subjects with molecularly confirmed CNGB3-associated achromatopsia and report the spectral domain optical coherence tomography (SD-OCT) findings in these individuals.

METHODS

Adults and children with CNGB3-achromatopsia underwent visual acuity testing, ocular motility assessments, video nystagmography, and SD-OCT imaging. Qualitative assessment of foveal structure was performed by grading SD-OCT images into one of five categories.

RESULTS

A total of 18 subjects (11 adults) were included. The majority demonstrated a phoria, with manifest strabismus present in only 3 subjects. The predominant nystagmus waveform within the cohort was pure pendular. Nine individuals demonstrated a mixture of waveforms. Nystagmus frequencies were 4-8 cycles/second, with no notable differences in eye movements between adults and children. SD-OCT imaging revealed a continuous ellipsoid zone (EZ) at the fovea in 2 subjects (grade 1) and EZ disruption (grade 2) in the remaining 16. Retinal structure characteristics were symmetrical in both eyes in each subject.

CONCLUSIONS

In our study cohort, nystagmus in CNGB3-associated achromatopsia had distinctive features, and the majority of subjects had retinal abnormalities at the fovea on SD-OCT. Early use of SD-OCT in the clinical work-up may eliminate the need for more invasive investigations, such as neuro-imaging.

An automated segmentation approach to calibrating infantile nystagmus waveforms

Infantile nystagmus (IN) describes a regular, repetitive movement of the eyes. A characteristic feature of each cycle of the IN eye movement waveform is a period in which the eyes are moving at minimal velocity. This so-called “foveation” period has long been considered the basis for the best vision in individuals with IN. In recent years, the technology for measuring eye movements has improved considerably, but there remains the challenge of calibrating the direction of gaze in tracking systems when the eyes are continuously moving. Identifying portions of the nystagmus waveform suitable for calibration typically involves time-consuming manual selection of the foveation periods from the eye trace. Without an accurate calibration, the exact parameters of the waveform cannot be determined. In this study, we present an automated method for segmenting IN waveforms with the purpose of determining the foveation positions to be used for calibration of an eye tracker. On average, the “point of regard” was found to be within 0.21° of that determined by hand-marking by an expert observer. This method enables rapid clinical quantification of waveforms and the possibility of gaze-contingent research paradigms being performed with this patient group.

Identification of a novel idiopathic congenital nystagmus‑causing missense mutation, p.G296C, in the FRMD7 gene

Exploring the genetic basis for idiopathic congenital nystagmus is critical for improving our understanding of its molecular pathogenesis. In the present study, direct sequencing using gene specific primers was performed in order to identify the causative mutations in two brothers from a Chinese family who had been diagnosed with idiopathic congenital nystagmus. A comprehensive ophthalmological examination, including eye movement recordings, fundus examination, and retinal optical coherence tomography imaging was also conducted, to characterize the disease phenotype. The results revealed that the two brothers exhibited clear signs of nystagmus without any other ocular anomalies. Direct sequencing revealed a G to T transition (c.886G>T) in exon 9 of the four‑point‑one, ezrin, radixin, moesin domain‑containing 7 (FRMD7) gene, which resulted in a conservative substitution of glycine to cysteine at codon 296 (p.G296C), leading to idiopathic congenital nystagmus in the two affected brothers. c.886G>T is a novel idiopathic congenital nystagmus‑inducing mutation in the FRMD7 gene. This finding expands the spectrum of known gene mutations in idiopathic congenital nystagmus, and may be useful for faster gene diagnosis, prenatal testing, the development of potential gene therapies, and for improving the understanding of the molecular pathogenesis of idiopathic congenital nystagmus.

The clinical evaluation of infantile nystagmus: What to do first and why

INTRODUCTION

Infantile nystagmus has many causes, some life threatening. We determined the most common diagnoses in order to develop a testing algorithm.

METHODS

Retrospective chart review. Exclusion criteria were no nystagmus, acquired after 6 months, or lack of examination.

DATA COLLECTED

pediatric eye examination findings, ancillary testing, order of testing, referral, and final diagnoses. Final diagnosis was defined as meeting published clinical criteria and/or confirmed by diagnostic testing. Patients with a diagnosis not meeting the definition were "unknown." Patients with incomplete testing were "incomplete." Patients with multiple plausible etiologies were "multifactorial." Patients with negative complete workup were "motor."

RESULTS

A total of 284 charts were identified; 202 met inclusion criteria. The three most common causes were Albinism (19%), Leber Congenital Amaurosis (LCA; 14%), and Non-LCA retinal dystrophy (13%). Anatomic retinal disorders comprised 10%, motor another 10%. The most common first test was MRI (74/202) with a diagnostic yield of 16%. For 28 MRI-first patients, nystagmus alone was the indication; for 46 MRI-first patients other neurologic signs were present. 0/28 nystagmus-only patients had a diagnostic MRI while 14/46 (30%) with neurologic signs did. The yield of ERG as first test was 56%, OCT 55%, and molecular genetic testing 47%. Overall, 90% of patients had an etiology identified.

CONCLUSION

The most common causes of infantile nystagmus were retinal disorders (56%), however the most common first test was brain MRI. For patients without other neurologic stigmata complete pediatric eye examination, ERG, OCT, and molecular genetic testing had a higher yield than MRI scan. If MRI is not diagnostic, a complete ophthalmologic workup should be pursued.

Nystagmus in pediatric patients: interventions and patient-focused perspectives

Nystagmus refers to involuntary, typically conjugate, often rhythmic oscillations of the eyes. The most common cause of nystagmus in children is infantile nystagmus syndrome (INS). INS presents within the first few months of life and is sometimes accompanied by an ocular condition associated with sensory impairment. Because this condition affects a person throughout life, it is important to understand the options available to manage it. This review focuses on the underlying nystagmus etiology, psychosocial and functional effects of nystagmus, as well as current principles of management, including optical, pharmacological, surgical, and rehabilitative options. Currently, the neural mechanisms underlying INS are not fully understood. Treatment options are designed to increase foveation duration or correct anomalous head postures; however, evidence is limited to mainly pre- and post-study designs with few objective comparisons of treatment strategies. Management of INS should be individualized. The decision on which treatment is best suited for a particular patient lies with the patient and his/her physician.