Nystagmus in childhood

Nystagmus in Clinical Practice: From Diagnosis to Treatment-A Comprehensive Review

Nystagmus, a common yet intricate ocular movement disorder, significantly contributes to visual morbidity in the paediatric and adult populations. Defined by involuntary, rhythmic, to-and-fro eye movements, this condition may manifest as an isolated anomaly or harbour more serious ocular or systemic pathologies. Its presence often provides vital diagnostic clues, emphasizing the importance of thorough evaluation to uncover potentially hidden underlying conditions. These mechanisms may range from dysfunction in the neural pathways to genetic mutations that affect ocular motor control. Nystagmus can profoundly affect visual acuity, spatial perception, and overall quality of life, leading to challenges in education, employment, and daily activities for the affected individuals. The diverse classifications of nystagmus, spanning congenital, acquired, and spontaneous forms, have distinct aetiologies, clinical features, and therapeutic considerations. For clinicians, a structured and systematic approach is essential for an accurate diagnosis and management. Advances in diagnostic modalities, including high-resolution imaging, electrodiagnostic studies, and eye tracking technologies, have enhanced our ability to delineate the underlying pathology. Similarly, therapeutic innovations such as pharmacological interventions, surgical techniques such as tenotomy, and even gene therapy and neurostimulation are opening new avenues for managing this disorder. A robust literature search was conducted using PubMed, MEDLINE, Cochrane, and EMBASE. The search strategy incorporated MeSH terms including "nystagmus", "classification", "diagnosis", and "treatment", and included both English and non-English articles up to December 2024. Studies were selected based on relevance to clinical features, pathophysiology, and recent advances in the field. This review offers a comprehensive exploration of the epidemiology, classification, clinical presentation, diagnostic strategies, and treatment of nystagmus. It also sheds light on recent advancements and emerging research, including the integration of artificial intelligence in clinical diagnostics. Ultimately, this review aims to serve as a practical clinical reference that enhances diagnostic accuracy and optimizes patient care within the ophthalmic and neuro-ophthalmic communities.

Nystagmus in infancy: causes, characteristics and main tools for diagnosis

BACKGROUND

Nystagmus in infancy may occur as part of an ocular condition, a neurological disorder or be idiopathic. The objective of our study was to evaluate the main causes for nystagmus in infants aged 0-1 year, the accompanying clinical characteristics and the effectiveness of different diagnostic tests used for reaching definite diagnosis.

METHODS

A retrospective study was conducted on medical records of infants who were seen at a tertiary hospital between 2016 and 2021. Clinical data were obtained including age at presentation, presence of strabismus, refractive errors, auxiliary tests performed to reach diagnosis, and initial versus final diagnosis.

RESULTS

This study included 147 infants. The most common ocular pathology causing nystagmus was albinism followed by inherited retinal diseases (IRDs). Main tests that helped reach diagnosis included clinical examination, genetic testing and electroretinogram (ERG). Vertical nystagmus was seen in 8/147 infants; among them 4 had an IRD as a final diagnosis. The most common associated clinical characteristics were high hypermetropia and strabismus.

CONCLUSIONS

The most common causes for nystagmus during the first year of age were albinism and IRDs. The most useful diagnostic tests to reach diagnosis were ERG together with genetic testing for IRDs and clinical ophthalmologic examination for albinism. IRDs play an important role as the cause for nystagmus in infants; this diagnosis can be often missed during the first months of life and a vertical nystagmus wave is commonly observed in this group. Nystagmus secondary to a neurologic condition is rare in this age group.

Clinical Spectrum and Molecular Characteristics of Inherited Ocular Diseases in a Cohort of Pediatric Patients With Infantile Nystagmus Syndrome

Purpose

Infantile nystagmus syndrome (INS), the most prevalent form of nystagmus in children, often indicates underlying ocular and neurological conditions. Genetic assessment plays a crucial role in clinical management, genetic counseling, and access to emerging gene-based therapies. This study aims to characterize the clinical and genetic landscape of inherited ocular diseases (IODs) in children with INS.

Methods

We retrospectively analyzed clinical and genetic data from 205 unrelated pediatric patients with INS enrolled in an IRB-approved nystagmus registry (2010-2024). All underwent next-generation sequencing (NGS) with targeted gene panels to detect pathogenic variants.

Results

The cohort comprised 117 males and 88 females (mean [SD] age, 8.85 [10.37] years). The most common INS-associated IODs included albinism (32%), Leber congenital amaurosis (LCA) (14%), and achromatopsia (14%). Genetic testing achieved a definitive diagnosis in 85 of 205 patients, yielding a molecular diagnostic rate of 41.5%. A total of 83 pathogenic and likely pathogenic variants were identified across 30 genes. The seven most frequently disease-causing genes-TYR, CNGB3, RPGR, GPR143, ABCA4, OCA2 and FRMD7-accounted for 65% of the genetically solved cases. Additionally, eight genes associated with LCA (AIPL1, CABP4, GUCY2D, IMPDH1, NMNAT1, RDH12, PRPH2, and RPGRIP1) contributed to 15% of these cases.

Conclusions

This study underscores the utility of NGS in diagnosing INS-associated IODs, providing essential insights for targeted interventions and identifying patients as candidates potentially eligible for ongoing gene-based therapy clinical trials.

Simplifying the Diagnosis of Pediatric Nystagmus with Fundus Photography

BACKGROUND/OBJECTIVES

To simplify diagnosing congenital and acquired nystagmus using fundus photographs.

METHODS

A retrospective study included patients with congenital or childhood-acquired nystagmus examined at a hospital-based ophthalmology clinic (September 2020-September 2023) with fundus photos taken. Exclusions were for incomplete data or low-quality images. Demographics, aetiology, orthoptic measurements, and ophthalmologic and neurological exams were reviewed. Two independent physicians graded fundus photos based on amplitude (distance between "ghost" images), the number of images visible, and the direction of nystagmus. Severity was rated on a 0-3 scale using qualitative and quantitative methods. Photographic findings were compared to clinical data, and statistical analysis used Mann-Whitney tests.

RESULTS

A total of 53 eyes from 29 patients (16 females, 13 males; mean age 12.5 years, range 3-65) were studied: 25 with binocular nystagmus and 3 with monocular nystagmus. Diagnoses included congenital (n = 15), latent-manifest (n = 3), neurologically associated (n = 2), and idiopathic (n = 9). Types observed were vertical (n = 5), horizontal (n = 23), rotatory (n = 10), and multidirectional (n = 15). Visual acuity ranged from 20/20 to no light perception. Fundus photos correlated with clinical diagnoses, aiding qualitative assessment of direction and amplitude and mitigating eye movement effects for clearer retinal detail visualization.

CONCLUSIONS

Fundus photography effectively captures nystagmus characteristics and retinal details, even in young children, despite continuous eye movements. Integrating fundus cameras into routine practice may enhance nystagmus diagnosis and management, improving patient outcomes.

Inter-Ocular Fixation Instability of Amblyopia: Relationship to Visual Acuity, Strabismus, Nystagmus, Stereopsis, Vergence, and Age

PURPOSE

Amblyopia damages visual sensory and ocular motor functions. One manifestation of the damage is abnormal fixational eye movements. Tiny fixation movements are normal; however, when these exceed a normal range, the behavior is labeled "fixation instability" (FI). Here we compare FI between normal and amblyopic subjects, and evaluate the relationship between FI and severity of amblyopia, strabismus angle, nystagmus, stereopsis, vergence, and subject age.

METHODS

Fixation eye movements were recorded using infrared video-oculography from 47 controls (15.3 ± 12.2 years of age) and 104 amblyopic subjects (13.3 ± 11.2 years of age) during binocular and monocular viewing. FI and vergence instability were quantified as the bivariate contour ellipse area (BCEA). We also calculated the ratio of FI between the 2 eyes: right eye/left eye for controls, amblyopic eye/fellow eye for amblyopes. Multiple regression analysis evaluated how FI related to a range of visuo-motor measures.

RESULTS

During binocular viewing, the FI of fellow and amblyopic eye, vergence instability, and inter-ocular FI ratios were least in anisometropic and most in mixed amblyopia (P < .05). Each correlated positively with the strabismus angle (P < .01). During monocular viewing, subjects with deeper amblyopia (P < .01) and larger strabismus angles (P < .05) had higher inter-ocular FI ratios. In all, 27% of anisometropic and >65% of strabismic/mixed amblyopes had nystagmus. Younger age and nystagmus increased FI and vergence instability (P < .05) but did not affect the inter-ocular FI ratios (P > .05).

CONCLUSIONS

Quantitative recording of perturbed eye movements in children reveal a major functional deficit linked to amblyopia. Imprecise fixation, measured as inter-ocular FI ratios, may be used as a robust marker for amblyopia and strabismus severity. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Infantile Nystagmus Syndrome-Associated Inherited Retinal Diseases: Perspectives from Gene Therapy Clinical Trials

Inherited retinal diseases (IRDs) are a clinically and genetically diverse group of progressive degenerative disorders that can result in severe visual impairment or complete blindness. Despite their predominantly monogenic inheritance patterns, the genetic complexity of over 300 identified disease-causing genes presents a significant challenge in correlating clinical phenotypes with genotypes. Achieving a molecular diagnosis is crucial for providing patients with definitive diagnostic clarity and facilitating access to emerging gene-based therapies and ongoing clinical trials. Recent advances in next-generation sequencing technologies have markedly enhanced our ability to identify genes and genetic defects leading to IRDs, thereby propelling the development of gene-based therapies. The clinical success of voretigene neparvovec (Luxturna), the first approved retinal gene therapy for RPE65-associated Leber congenital amaurosis (LCA), has spurred considerable research and development in gene-based therapies, highlighting the importance of reviewing the current status of gene therapy for IRDs, particularly those utilizing adeno-associated virus (AAV)-based therapies. As novel disease-causing mutations continue to be discovered and more targeted gene therapies are developed, integrating these treatment opportunities into the standard care for IRD patients becomes increasingly critical. This review provides an update on the diverse phenotypic-genotypic landscape of IRDs, with a specific focus on recent advances in the understanding of IRDs in children with infantile nystagmus syndrome (INS). We highlight the complexities of the genotypic-phenotypic landscape of INS-associated IRDs, including conditions such as achromatopsia, LCA, congenital stationary night blindness, and subtypes of retinitis pigmentosa. Additionally, we provide an updated overview of AAV-based gene therapies for these diseases and discuss the potential of gene-based therapies for underlying IRDs that lead to INS, offering a valuable resource for pediatric patients potentially eligible for ongoing clinical trials.

Visual Impairment in Women with Turner Syndrome-A 49-Year Literature Review

Aim: Among the severe organ complications occurring in patients with Turner syndrome (TS), ophthalmic dysmorphia and visual impairment are usually marginalized. There are only a few studies that take into account the prevalence of ophthalmic disorders in female patients with TS. Material and methods: Articles in PubMed, Scholar, and Website were reviewed, considering the prevalence of various ocular disorders in patients with X chromosome deficiency. Current standards for the management of patients with TS in the context of the prevalence of ophthalmic disorders were also analyzed. Results: Identification of visual impairment in people is important because it significantly impairs quality of life (QoL) along with other health problems. QoL affects cognitive and behavioral functioning and significantly increases self-esteem, acceptance of treatment, and, consequently, physical and mental health. Low self-esteem makes patients feel helpless and unable to plan their social development. Patients with TS are relatively more frequently diagnosed with various eye defects compared to the healthy population. Therefore, special attention should be paid to the early assessment of the visual system in people with TS to eliminate any factors that could potentially impair their QoL. Conclusions: Patients with TS should be referred to specialist ophthalmologists, pediatricians, or optometrists for preventive care or early treatment of visual impairment. The authors point out the need for comprehensive ophthalmological examinations as standard management in patients with TS.

ACR Appropriateness Criteria® Orbital Imaging and Vision Loss-Child

Orbital disorders in children consist of varied pathologies affecting the orbits, orbital contents, visual pathway, and innervation of the extraocular or intraocular muscles. The underlying etiology of these disorders may be traumatic or nontraumatic. Presumed location of the lesion along with the additional findings, such as eye pain, swelling, exophthalmos/enophthalmos, erythema, conjunctival vascular dilatation, intraocular pressure, etc, help in determining if imaging is needed, modality of choice, and extent of coverage (orbits and/or head). Occasionally, clinical signs and symptoms may be nonspecific, and, in these cases, diagnostic imaging studies play a key role in depicting the nature and extent of the injury or disease. In this document, various clinical scenarios are discussed by which a child may present with an orbital or vision abnormality. Imaging studies that might be most appropriate (based on the best available evidence or expert consensus) in these clinical scenarios are also discussed. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Modernizing the evaluation of infantile nystagmus: the role of handheld optical coherence tomography

BACKGROUND

Infantile nystagmus syndrome can be associated with an afferent problem (anterior or posterior segment) or constitute an isolated idiopathic disorder. With a normal ophthalmic examination, current guidelines recommend electroretinography (ERG) rather than magnetic resonance (MRI) for preliminary workup. Given the limited use of optical coherence tomography (OCT) in preverbal children, the purpose of this study was to evaluate the role of handheld OCT (HH-OCT) in the initial diagnostic evaluation of infantile nystagmus.

METHODS

In this cross-sectional case series, the medical records of all children with infantile nystagmus and HH-OCT imaging at the Duke Eye Center from August 2016 to July 2021 were retrospectively reviewed. Children with anterior segment disorders or obvious retina/optic nerve structural pathology, bilateral ophthalmoplegia, or Down syndrome were excluded. Two masked pediatric ophthalmologists graded HH-OCT images for optic nerve head and macular abnormalities. A neuro-ophthalmologist reviewed clinical findings of each patient's presenting visit and recommended appropriate testing (MRI vs ERG), initially without, and again with HH-OCT image review.

RESULTS

A total of 39 cases were included, with mean presenting age of 1.3 years. Final diagnoses included retinal or foveal abnormalities (7), optic nerve pathology (13), idiopathic (10), or unknown (9). HH-OCT findings included optic nerve hypoplasia (1), optic nerve elevation (3), persistence of the inner layers at the fovea (9), thin ganglion cell layer (8), ellipsoid zone abnormality (3), and thin choroid (1). HH-OCT findings altered initial clinical-only management in 16 cases (41%), including avoiding MRI (5) and ERG (10) testing.

CONCLUSIONS

Our results suggest that HH-OCT has the potential to augment and streamline the evaluation of infantile nystagmus.

Managing the apparently blind child presenting in the first year of life: A review

Severe vision impairment and blindness in childhood have a significant health burden on the child, family and society. This review article seeks to provide a structured framework for managing the apparently blind child presenting in the first year of life, starting from a comprehensive history and examination. Different investigation modalities and the increasingly important role of genetics will also be described, in addition to common causes of severe vision impairment. Crucially, a systematic approach to the blind infant is key to correct diagnoses and timely management. Incorrect diagnoses can be costly to all involved, however it is important to note that diagnoses can change with ongoing follow-up and investigations. Furthermore, the modern age of ophthalmology requires a multi-disciplinary approach and close collaboration with specialists including paediatricians, neurologists and geneticists, in addition to rehabilitation and low vision services, to ensure the best care for these vulnerable infants.

Differences of ocular oscillations and neuro-retinal structures in patients with nystagmus caused by GPR143 and FRMD7 gene variants

PURPOSE

Mutations of G protein-coupled receptor 143 (GPR143) and FERM domain containing 7 (FRMD7) may result in congenital nystagmus (CN) in the first 6 months of life. We aimed to compare the differences in ocular oscillations between patients with these two gene mutations as well as the functional and structural changes in their retinas and visual pathways.

METHODS

Medical records were retrospectively reviewed to identify patients of congenital nystagmus with confirmed mutations in either GPR143 or FMRD7 genes from January 2018 to May 2023. The parameters of the ocular oscillations were recorded using Eyelink 1000 Plus. The retinal structure and function were evaluated using optical coherence tomography and multi-focal electroretinography (mERG). The visual pathway and optical nerve projection were evaluated using visual evoked potentials. The next-generation sequencing technique was used to identify the pathogenic variations in the disease-causing genes for CN.

RESULTS

Twenty nystagmus patients of GPR143 and 21 patients of FMRD7 who had been confirmed by molecular testing between January 2018 and May 2023 were included. Foveal hypoplasia was detected only in patients with the GPR143 pathogenic variant. mERG examination showed a flat response topography in the GPR143 group compared to the FRMD7 group. VEP showed that bilateral amplitude inconsistency was detected only in the patients with GPR143 gene mutation. The amplitude and frequency of the ocular oscillations were not found to differ between patients with two different genetic mutations.

CONCLUSIONS

Although the etiology and molecular mechanisms are completely different between CN patients, they may have similar ocular oscillations. A careful clinical examination and electrophysiological test will be helpful in making a differential diagnosis. Our novel identified variants will further expand the spectrum of the GPR143 and FRMD7 variants.

A Novel Type of Autosomal Dominant Episodic Nystagmus Segregating with a Variant in the FRMD5 Gene

To describe the phenotype of a novel form of autosomal dominant episodic nystagmus and to identify the potential genetic aetiology. We identified several individuals in a large Swedish family affected by episodic nystagmus. In total, 39 family members from five generations were invited to participate in the study, of which 17 were included (12 affected and 5 unaffected). The phenotype of the nystagmus was described based on data collected from family members through questionnaires, interviews, clinical examinations and from video recordings of ongoing episodes of nystagmus. Whole genome sequencing (WGS) and further Sanger sequencing for segregation of the identified candidate variants was performed in eight participants (six affected and two unaffected). The 12 affected participants showed a phenotype with episodic nystagmus of early onset. A vertical jerk nystagmus with variable amplitude and frequency was characterized in the analysed video material. No other eye pathology or other disease that could explain the episodic nystagmus was identified among the family participants. Genetic analysis identified a missense variant (p.Ser375Phe) in the gene FRMD5, which segregated with the disease in the eight individuals analysed, from three generations. We describe a novel autosomal dominant form of early onset episodic nystagmus and suggest the FRMD5 gene as a strong candidate gene for this disorder.

Multifractal characterization of nystagmus eye movements

In this work, we investigate the multifractal properties of eye movement dynamics of children with infantile nystagmus, particularly the fluctuations of its velocity. The eye movements of three children and one adult with infantile nystagmus were evaluated in a simple task in comparison with 28 children with no ocular pathologies. Four indices emerge from the analysis: the classical Hurst exponent, the singularity strength corresponding to the maximum of the singularity spectrum, the asymmetry of the singularity spectrum, and the multifractal strength, each of which characterizes a particular aspect of eye movement dynamics. Our findings indicate that, when compared to children with no ocular pathologies, patients with infantile nystagmus present lower values of all indices. Except for the multifractal strength, the difference in the remaining indices is statistically significant. To test whether the characterization of patients with infantile nystagmus in terms of multifractality indices allows them to be distinguished from children without ocular pathologies, we performed an unsupervised clustering analysis and classified the subjects using supervised clustering techniques. The results indicate that these indices do, indeed, distinctively characterize the eye movements of patients with infantile nystagmus.

Infantile nystagmus syndrome: An observational, retrospective, multicenter study

SIGNIFICANCE

This multicenter study assessed clinical and psychological aspects of infantile nystagmus syndrome (INS) focusing on its management and nonsurgical treatment.

PURPOSE

This study aimed to assess clinical features, management, relationship life, and psychological impact in a group of patients with nystagmus onset in pediatric age.

METHODS

This observational study included patients diagnosed with INS referred to two Italian centers from January 1, 2017, to December 31, 2020. Ophthalmologic and orthoptic features and impact of visual function on quality of life, according to nystagmus-specific nystagmus quality of life questionnaire, were analyzed within the overall sample and in any of INS subgroups.

RESULTS

Forty-three patients were included; 65.1% of them had idiopathic INS (IINS), and 34.9% had INS associated with ocular diseases (INSOD). The median age was 15.4 years (interquartile range [IQR], 10.4 to 17.3 years), significantly different between groups (median, 15.8 years among those with IINS vs. 12.3 years among those with INSOD; p<0.001). In the INSOD subgroup, strabismus was significantly more prevalent (93.3 vs. 57.1%; p=0.017). Binocular distance best-corrected visual acuity in primary position was significantly higher in the IINS subsample (p<0.001). Such behavior was further confirmed at anomalous head position evaluation (p<0.001). At near best-corrected visual acuity assessment, differences between groups were more remarkable in primary position (p<0.001) than in anomalous head position. Contrast sensitivity showed significantly higher values in the IINS subgroup (p<0.001). The nystagmus quality of life questionnaire disclosed a significantly lower score in IINS as compared with INSOD (median total score, 90.5 [IQR, 84 to 97] vs. 94 [IQR, 83.0 to 96.5]; p<0.001).

CONCLUSIONS

The IINS group showed significantly better ophthalmologic and orthoptic outcomes than the INSOD group. The psychological and quality-of-life impact was instead significantly greater in the IINS group. To the best of our knowledge, this is the first multicenter study investigating the clinical features of IIN and comparing the two main subgroups, IINS and INSOD.

Nystagmus in children with primary brain tumours in Denmark between 2007 and 2017

BACKGROUND

The aim of the study was to evaluate the prevalence, clinical characteristics, and diagnostic importance of nystagmus in children with brain tumours.

METHODS

A nation-wide retrospective review of all children diagnosed with a brain tumour between January the 1st, 2007 and December 31st, 2017, in Denmark. Data is based on information from the Danish Childhood Cancer Registry, hospital records from paediatric- and ophthalmological departments, and records from private ophthalmologists.

RESULTS

Nystagmus was observed in 13.7% (60/437) of children with a brain tumour. In 50/60 children (83.3%) nystagmus was an incidental finding at the clinical examination and only in 10/60 children (16,7%) were nystagmus noticed by patient/caregivers prior to the clinical examination. In 38/60 children nystagmus was observed before the brain tumour diagnosis, most often (16/38, 42%) the same day as the diagnosis was made. In 22/60 children nystagmus was found after the brain tumour diagnosis (prior to any treatment) with a median of four days (range 0-47) after the brain tumour diagnosis. Nystagmus was most commonly binocular (56/60, 93.3%) and gaze-evoked (43/60, 71.7%). The median number of additional symptoms and/or clinical findings was five (range 0-11).

CONCLUSION

Nystagmus is frequent in children with brain tumours and is typically accompanied by other symptoms and clinical signs. However, nystagmus is often first recognized by the ophthalmologist late in the time course. Therefore, raising awareness of the importance of looking for nystagmus in children with unspecific neurological symptoms might contribute to increased suspicion of brain tumour and thereby faster diagnosis.

Visual function in children with Joubert syndrome

AIM

To describe visual function in children with Joubert syndrome and to investigate its possible association with diagnostic and developmental aspects.

METHOD

This retrospective cross-sectional work included 59 patients (33 male; mean age 9 years 2 months, standard deviation 6 years 3 months, range 4 months to 23 years) diagnosed with Joubert syndrome from January 2002 to December 2020. Data about clinical (neurological, neuro-ophthalmological, developmental/cognitive) and diagnostic (e.g. genetic testing, neuroimaging, systemic involvement) evaluations were collected in a data set during a review of medical records. Clinical and diagnostic variables were described in terms of raw counts and percentages. A χ2 test was conducted to investigate their association with neuropsychological skills.

RESULTS

Ocular motor apraxia was highly represented in our cohort (75%), with a high prevalence of refractive defects and retinal abnormalities. Developmental delay/intellectual disability was frequent (in 69.5% of the sample), associated with retinal dystrophy (p = 0.047) and reduced visual acuity both for near (p = 0.014) and for far distances (p = 0.017).

INTERPRETATION

On the basis of the relevance of oculomotor and perceptual alterations and their impact on overall and cognitive impairment, we encourage early and multidisciplinary assessment and follow-up of visual function in children with Joubert syndrome. This would help in planning a personalized rehabilitation to sustain functional vision. Further studies will be important to explore the link between biological aspects and global functioning in children with Joubert syndrome.

WHAT THIS PAPER ADDS

Perceptual deficits and oculomotor impairments frequently coexist in Joubert syndrome. Retinal dysfunction may be present despite the absence of funduscopic abnormalities. Both perceptual and oculomotor impairments negatively affect cognitive development in Joubert syndrome.

Truncated FRMD7 proteins in congenital Nystagmus: novel frameshift mutations and proteasomal pathway implications

Idiopathic congenital nystagmus (ICN) manifests as involuntary and periodic eye movements. To identify the genetic defect associated with X-linked ICN, Whole Exome Sequencing (WES) was conducted in two affected families. We identified two frameshift mutations in FRMD7, c.1492dupT/p.(Y498Lfs*15) and c.1616delG/p.(R539Kfs*2). Plasmids harboring the mutated genes and qPCR analysis revealed mRNA stability, evading degradation via the NMD pathway, and corroborated truncated protein production via Western-blot analysis. Notably, both truncated proteins were degraded through the proteasomal (ubiquitination) pathway, suggesting potential therapeutic avenues targeting this pathway for similar mutations. Moreover, we conducted a comprehensive analysis, summarizing 140 mutations within the FRMD7 gene. Our findings highlight the FERM and FA structural domains as mutation-prone regions. Interestingly, exons 9 and 12 are the most mutated regions, but 90% (28/31) mutations in exon 9 are missense while 84% (21/25) mutations in exon 12 are frameshift. A predominant occurrence of shift code mutations was observed in exons 11 and 12, possibly associated with the localization of premature termination codons (PTCs), leading to the generation of deleterious truncated proteins. Additionally, our conjecture suggests that the loss of FRMD7 protein function might not solely drive pathology; rather, the emergence of aberrant protein function could be pivotal in nystagmus etiology. We propose a dependence of FRMD7 protein normal function primarily on its anterior domain. Future investigations are warranted to validate this hypothesis.

Eyetracking-enhanced VEP for nystagmus

Visual evoked potentials (VEPs) are an important prognostic indicator of visual ability in patients with nystagmus. However, VEP testing requires stable fixation, which is impossible with nystagmus. Fixation instability reduces VEP amplitude, and VEP reliability is therefore low in this important patient group. We investigated whether VEP amplitude can be increased using an eye tracker by triggering acquisition only during slow periods of the waveform. Data were collected from 10 individuals with early-onset nystagmus. VEP was obtained under continuous (standard) acquisition, or triggered during periods of low eye velocity, as detected by an eye tracker. VEP amplitude was compared using Bonferroni corrected paired samples t-tests. VEP amplitude is significantly increased when triggered during low eye velocity (95% CI 1.42-6.83 µV, t(15) = 3.25, p = 0.0053). This study provides proof-of-concept that VEP amplitude (and therefore prognostic reliability) can be increased in patients with early onset nystagmus by connecting an eye tracker and triggering acquisition during periods of lower eye velocity.

Demographic and Clinical Characteristics of 600 Children With Nystagmus

PURPOSE

To characterize a large, international cohort of children with nystagmus.

METHODS

Data were collected from a single-center, prospectively developed database on patients with nystagmus. Outcome variables for this study included: (1) demographic characteristics, (2) nystagmus type, (3) clinical characteristics, (4) associated ophthalmic conditions, (5) associated non-ophthalmic conditions, (6) special testing findings, and (7) treatments.

RESULTS

Six hundred patients from 38 states and 30 countries were included. Age ranged from birth to younger than 18 years (mean: 15.2 years), 58% were female, 55% were race other than White, 75% had infantile nystagmus syndrome, 17% had neurologically significant nystagmus, 7% had fusion maldevelopment nystagmus syndrome, 64% had strabismus, 56% had an anomalous head posture, 94% had a significant refractive error, 64% had an associated ophthalmic abnormality (excluding ametropia), and 45% had an associated systemic condition. Special testing showed abnormalities in 67% and 95% had treatment directed at their nystagmus.

CONCLUSIONS

The most common diagnosis in this cohort is neurologically non-significant infantile nystagmus syndrome. Eye movement recordings provide a path toward accurate diagnosis and classification. There was a high prevalence of underlying ocular and/or systemic conditions requiring ophthalmic special testing as part of a diagnostic routine. Clinical treatments are available to most patients. [J Pediatr Ophthalmol Strabismus. 2023;60(6):406-410.].

The long-term outcomes of the Anderson-Kestenbaum procedure

Introduction

Nystagmus is an involuntary, conjugated, rhythmic movement of the eye that can be idiopathic or secondary to ocular or neurologic pathologies. Patients with nystagmus often have a position of gaze in which their symptoms are dampened or absent, referred to as the "null zone." The Anderson-Kestenbaum procedure is a bilateral recess-resect procedure of the four horizontal rectus muscles which aims to bring the null position into the primary gaze. This study aims to further elucidate long-term outcomes and factors associated with optimal postoperative outcomes.

Methods

Patients with a diagnosis of nystagmus and a surgical code for strabismus between June 1990 and August 2017 were considered for inclusion in the study. Patients were included if they had undergone the Anderson-Kestenbaum procedure and had follow-up lasting at least 24 months post-operatively. Data collected included demographic information, characteristics of the nystagmus, underlying etiology of nystagmus, and pre-and post-operative measurements.

Results

25 patients were included. At their last recorded follow-up, 44% of patients achieved an optimal surgical outcome -an abnormal head position of 10 degrees or less. 88% of patients showed an overall improvement in their head posture at the last follow-up. The absence of an abnormal head position at the visit closest to 24 months post-operatively was found to be significantly associated with the lack of a significant head position at the last follow-up visit. Optimal surgical outcomes were not significantly associated with the underlying diagnosis, the direction of the abnormal head position, or the type of nystagmus.

Discussion

The relatively long follow-up of this cohort allows this study to further elucidate the long-term outcomes of the Anderson-Kestenbaum procedure. Overall, our results suggest that although improvement in head position post-operatively is likely, it is still expected that many patients will have a residual abnormal head position after the procedure. The results of this study are helpful in counseling patients, especially knowing that if they do not have a significant head position at 24 months follow-up, they are unlikely to develop one. However, due to the small sample size, larger cohorts and more standardized follow-up may provide further insight into the procedure's outcomes.

Novel mutations of the X-linked genes associated with early-onset high myopia in five Chinese families

PURPOSE

To report novel pathogenic variants of X-linked genes in five Chinese families with early-onset high myopia (eoHM) by using whole-exome sequencing and analyzing the phenotypic features.

METHODS

5 probands with X-linked recessive related eoHM were collected in Ningxia Eye Hospital from January 2021 to June 2022. The probands and their family members received comprehensive ophthalmic examinations,and DNA was abstracted from patients and family members. Whole-exome sequencing was performed on probands to screen the causative variants, and all suspected pathogenic variants were determined by Sanger sequencing and co-segregation analysis was performed on available family members. The pathogenicity of novel variants was predicted using silico analysis and evaluated according to ACMG guidelines. RT-qPCR was used to detect differences in the relative mRNAs expression of candidate gene in mRNAs available with the proband and family members in the pedigree 2. The relationship between genetic variants and clinical features was analyzed.

RESULTS

All probands were male, and all pedigrees conformed to an X-linked recessive inheritance pattern. They were diagnosed with high myopia at their first visits between 4 and 7 years old. Spherical equivalent ranged between - 6.00D and - 11.00D.The five novel hemizygous variants were found in the probands, containing frameshift deletion variant c.797_801del (p.Val266Alafs*75) of OPN1LW gene in the pedigree 1, nonsense variant c.513G > A (p.Trp171Ter)of RP2 gene in the pedigree 2, missense variant c.98G > T (p.Cys33Phe) of GPR143 gene in the pedigree 3, frameshift deletion variant c.1876_1877del (p.Met626Valfs*22) of FRMD7 gene in the pedigree 4 and inframe deletion variant c.670_ 675del (p.Glu192_ Glu193del) of HMGB3 gene in the pedigree 5. All variants were classified as pathogenic or likely pathogenic by the interpretation principles of HGMD sequence variants and ACMG guidelines. In family 2, RT-qPCR showed that the mRNA expression of RP2 gene was lower in the proband than in other normal family members, indicating that such variant caused an effect on gene function at the mRNA expression level. Further clinical examination showed that pedigrees 1, 2, 3, and 4 were diagnosed as X-linked recessive hereditary eye disease with early-onset high myopia, including quiescent cone dysfunction, retinitis pigmentosa, ocular albinism, and idiopathic congenital nystagmus respectively. The pedigree 5 had eoHM in the right eye and ptosis in both eyes.

CONCLUSION

In this paper,we are the first to report five novel hemizygous variants in OPN1LW, RP2, GPR143, FRMD7, HMGB3 genes are associated with eoHM. Our study extends the genotypic spectrums for eoHM and better assists ophthalmologists in assessing, diagnosing, and conducting genetic screening for eoHM.

Visual Function and Neuropsychological Profiling of Idiopathic Infantile Nystagmus

Though considered a benign condition, idiopathic infantile nystagmus (IIN) may be associated with decreased visual acuity and oculo-motor abnormalities, resulting in developmental delays and poor academic performance. Nevertheless, the specific visual function profile of IIN and its possible impact on neuropsychological development have been poorly investigated. To fill this gap, we retrospectively collected the clinical data of 60 children presenting with IIN over a 10-year period (43 male; mean age of 7 years, range of 2 months-17 years, 9 months). The majority of the subjects in our cohort presented with reduced visual acuity for far distances and normal visual acuity for near distances, associated with oculo-motor abnormalities. The overall scores of cognitive and visual-cognitive tests were in the normal range, but revealed peculiar cognitive and visual-cognitive profiles, defined by specific frailties in processing speed and visual-motor integration. The same neuropsychological profiles characterize many neurodevelopmental disorders and may express a transnosographic vulnerability of the dorsal stream. As the first study to explore the neuropsychologic competencies in children with IIN, our study unveils the presence of subclinical frailties that need to be addressed to sustain academic and social inclusion.

A retinal origin of nystagmus-a perspective

Congenital nystagmus is a condition where the eyes of patients oscillate, mostly horizontally, with a frequency of between 2 and 10 Hz. Historically, nystagmus is believed to be caused by a maladaptation of the oculomotor system and is thus considered a disease of the brain stem. However, we have recently shown that congenital nystagmus associated with congenital stationary night blindness is caused by synchronously oscillating retinal ganglion cells. In this perspective article, we discuss how some details of nystagmus can be accounted for by the retinal mechanism we propose.

Grasping behavior does not recover after sight restoration from congenital blindness

We investigated whether early visual input is essential for establishing the ability to use predictions in the control of actions and for perception. To successfully interact with objects, it is necessary to pre-program bodily actions such as grasping movements (feedforward control). Feedforward control requires a model for making predictions, which is typically shaped by previous sensory experience and interaction with the environment.¹ Vision is the most crucial sense for establishing such predictions.^2,3 We typically rely on visual estimations of the to-be-grasped object's size and weight in order to scale grip force and hand aperture accordingly.^4,5,6 Size-weight expectations play a role also for perception, as evident in the size-weight illusion (SWI), in which the smaller of two equal-weight objects is misjudged to be heavier.^7,8 Here, we investigated predictions for action and perception by testing the development of feedforward controlled grasping and of the SWI in young individuals surgically treated for congenital cataracts several years after birth. Surprisingly, what typically developing individuals do easily within the first years of life, namely to adeptly grasp new objects based on visually predicted properties, cataract-treated individuals did not learn after years of visual experience. Contrary, the SWI exhibited significant development. Even though the two tasks differ in substantial ways, these results may suggest a potential dissociation in using visual experience to make predictions about an object's features for perception or action. What seems a very simple task-picking up small objects-is in truth a highly complex computation that necessitates early structured visual input to develop.

X-linked FRMD7 gene mutation in idiopathic congenital nystagmus and its role in eye movement: A case report and literature review

Background

Idiopathic congenital nystagmus (ICN) is an inherited disorder characterized by uncontrollable binocular conjugating oscillation. X-linked idiopathic congenital nystagmus is one of the most prevalent types of ICN. Elucidation of the genetic mechanisms involved in ICN will enhance our understanding of its molecular etiology.

Case presentation

We report a girl with uncontrollable binocular oscillation and anomalous head posture, then presented a novel heterozygous missense variant (c.686G>T) within the mutation-rich region of the FERM domain containing 7 (FRMD7) gene in her family member. The girl received occlusion therapy and surgical operation which balanced her binocular vision and corrected the anomalous head posture.

Conclusions

This is the first report on a mutation (c.686G>T) caused the substitution of Arg (R) with Leu (L) at position 229 (p.R229L) of the FRMD7 protein in a patient with ICN.

Micro chromosomal deletions at the NYS7 locus and autosomal dominant nystagmus

Nystagmus is an ocular condition characterized by bilateral involuntary ocular oscillation which can severely affect vision. When not associated with other ocular or systemic diseases, it is referred to as idiopathic or congenital motor nystagmus (CMN). Genome-wide linkage studies have previously identified several loci associated with CMN, however the genes responsible for some of these loci have yet to be identified. We have examined a large, five-generation family with autosomal dominant CMN. Our purpose was to characterize the clinical manifestations and reveal the molecular basis of the disease in this family. In addition to full ophthalmic examination and imaging, molecular analysis included copy number variation analysis, linkage studies, and Sanger sequencing. Expression analyses of candidate genes was done by real-time PCR. Of the 68 family members, 27 subjects in five-generations had CMN, in line with an autosomal dominant inheritance pattern. Molecular analysis was performed on 27 members, 15 of them affected by CMN. Copy number variation analysis using array comparative genomic hybridization (aCGH) revealed a novel deletion located on 1q32 (NYS7) among affected individuals. Linkage analysis using polymorphic markers demonstrated full segregation with a heterozygous haplotype in all affected patients, with a LOD score of >5. Sanger sequencing of affected subjects revealed a novel deletion of 732,526 bp in the linkage interval. No protein-coding genes exist within the deleted region; however, the deletion disrupts topologically associated domains encompassing the gene NR5A2 and the non-protein coding MIR181A. Both are strongly associated with other genes expressed in the retina such as PROX1, which in turn is also associated with genes related to nystagmus such as PAX6. We therefore hypothesized that the deletion might affect NR5A2 and MIR181A expression, causing CMN. Expression analysis by real-time PCR showed significantly lower expression of NR5A2, and significantly higher expression of PROX1 among patients compared with controls. To conclude, among a large five-generation family with autosomal dominant CMN, a large deletion in the interval of NYS7 was linked with the disease. No protein-coding genes exist inside the deleted region, and so the exact mechanism in which CMN is caused is uncertain. Based on topological association and expression analyses we suggest a possible mechanism for the pathogenesis.

[Nystagmus in Children - a Survey]

Nystagmus describes an involuntary, periodic movement of one or both eyes. About 1/600 children and adolescents have nystagmus, most of them idiopathic infantile nystagmus (IIN), also called "congenital nystagmus", which can be caused by mutations in the FRMD7 gene. Other frequent forms of nystagmus are latent nystagmus, which is usually associated with infantile strabismus, and nystagmus associated with albinism. Sometimes difficult to distinguish in young infants is a sensory nystagmus, where a defect in the visual system reduces vision and causes nystagmus. Causes include retinal dystrophies, congenital stationary night blindness and structural ocular defects including optic nerve hypoplasia or dense bilateral congenital cataracts. Unilateral nystagmus can be the sign of an anterior visual pathway lesion. Seesaw nystagmus may be associated with suprasellar and mesodiencephalic lesions and - rarely - with retinal dystrophies.The ophthalmology plays a key role in identifying the form of nystagmus. Children with new onset nystagmus, with spasmus nutans, with vertical or unilateral nystagmus and those with seesaw nystagmus require neurologic evaluation including imaging of the brain.The treatment of nystagmus depends on the underlying cause. Even minor refractive errors should be corrected, contact lenses offer advantages over glasses.Gabapentin and memantine, possibly also carbonic anhydrase inhibitors, are effective in treating IIN, nystagmus in albinism and sensory nystagmus. Nevertheless, pharmacologic treatment of nystagmus is rarely used in children; the reasons are the limited effects on vision, the need for lifelong therapy, and potential side effects. Eye muscle surgery (Anderson procedure, Kestenbaum procedure) can correct a nystagmus-related anomalous head posture. The concept of "artifical divergence" of Cüppers may help to decrease nystagmus intensity in patients whose nystagmus dampens with convergence. The four-muscle-tenotomy, which involves disinsertion and reinsertion of the horizontal muscles at the original insertion of both eyes, has a proven but limited positive effect on visual acuity.

Nystagmus bei Kindern – eine Übersicht

Nystagmus ist definiert als unwillkürliche, periodische Bewegung, bei der eines oder beide Augen vom Fixationspunkt wegdriften (sog. Drift). Auf die Drift, die langsame Phase, folgt entweder eine schnelle, refixierende Bewegung (sog. Refixationssakkade oder schnelle Phase) oder eine langsamere Bewegung zur Wiederaufnahme der Fixation. In dieser Übersichtsarbeit sollen die wichtigsten Formen von Nystagmus bei Kindern erörtert werden, für eine Übersicht bei Erwachsenen sei auf 1 verwiesen.

A dynamical method to objectively assess infantile nystagmus based on eye tracking. A pilot study

PURPOSE

The purpose of this research is to propose a new method for the easy, inexpensive and objective quantification of nystagmus using eye-tracking records collected during a simple reading task that could be implantable in clinical practice to assess patients with nystagmus.

METHODS

This is a prospective, observational pilot study. Eye movements of 4 nystagmus patients and 9 healthy children during a reading task (a paragraph with 82 words) on a 15'' monitor were collected and compared. Data are time series indicating the gaze position on the screen. Two quantifiers were proposed: IndS (based on the speed of movements) and IndF (based on the variation of the gaze trajectory).

RESULTS

The indices proposed reflect differences in the behavior of eye movements between the two groups. Nystagmus patients present higher values of IndS - indicating smaller number of slow movements (16% of movements with speeds <0.33 1/s for nystagmus and 85% for the control group, with p = 0.01) - and higher values of IndF - indicating higher gaze fluctuation (p = 0.01). Differences were not related with reading speed as show the mean and standard deviation: the nystagmus group required 115±45 s to complete the task and the control group 151±85 s; p = 0.73.

CONCLUSIONS

The proposed indices provide a new method that allows an objective assessment of nystagmus, with potential use in clinical and research practice to improve the follow-up of patients by monitoring the nystagmus over time or treatment.

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.

Congenital Stationary Night Blindness: Clinical and Genetic Features

Congenital stationary night blindness (CSNB) is an inherited retinal disease (IRD) that causes night blindness in childhood with heterogeneous genetic, electrophysical, and clinical characteristics. The development of sequencing technologies and gene therapy have increased the ease and urgency of diagnosing IRDs. This study describes seven Taiwanese patients from six unrelated families examined at a tertiary referral center, diagnosed with CSNB, and confirmed by genetic testing. Complete ophthalmic exams included best corrected visual acuity, retinal imaging, and an electroretinogram. The effects of identified novel variants were predicted using clinical details, protein prediction tools, and conservation scores. One patient had an autosomal dominant CSNB with a RHO variant; five patients had complete CSNB with variants in GRM6, TRPM1, and NYX; and one patient had incomplete CSNB with variants in CACNA1F. The patients had Riggs and Schubert-Bornschein types of CSNB with autosomal dominant, autosomal recessive, and X-linked inheritance patterns. This is the first report of CSNB patients in Taiwan with confirmed genetic testing, providing novel perspectives on molecular etiology and genotype-phenotype correlation of CSNB. Particularly, variants in TRPM1, NYX, and CACNA1F in our patient cohort have not previously been described, although their clinical significance needs further study. Additional study is needed for the genotype-phenotype correlation of different mutations causing CSNB. In addition to genetic etiology, the future of gene therapy for CSNB patients is reviewed and discussed.

Amblyopia and fixation eye movements

Amblyopia is a neurodevelopmental disorder caused by abnormal visual experience in early life that affects 3-5% of the population. Amblyopia results in a host of monocular and binocular visual afferent function deficits including reduced visual acuity, contrast sensitivity, depth perception, interocular suppression, and efferent function abnormalities such as unstable and inaccurate fixation. Conventional treatments such as patching therapy and newer dichoptic treatments are not always successful as 30-40% of patients experience recurrence/regression of amblyopia. There are numerous review articles focused on visual afferent function deficits and treatment modalities and outcomes in amblyopia. Recently, the advent of high spatial and temporal resolution eye trackers has spurred studies on fixation eye movements (FEMs) in healthy controls and neurologic and ophthalmic disorders. In this focused review, we will summarize studies evaluating FEM abnormalities in amblyopia. We will first describe the common devices and techniques used to quantify fixation abnormalities, and then highlight the importance of systematically evaluating the eye movements under different viewing conditions and describe the parameters crucial in assessing FEM abnormalities in amblyopia. We will summarize the evidence suggesting that FEM abnormalities are not limited to the amblyopic eye only but also affects the fellow eye and that FEM abnormalities can serve as biomarkers to predict the impact of amblyopia on visual functions. Beyond diagnosis, we will discuss the treatment and prognostic implications of the evaluation of FEM abnormalities in clinical practice.

Correction of horizontal and torsional compensatory head posture in infantile nystagmus syndrome using horizontal rectus muscle recession and resection with vertical transposition

Infantile nystagmus syndrome (INS) is often characterized by an identifiable null zone. When the null zone is not in the straight-ahead gaze, a compensatory head posture (CHP) is adopted by the patient to achieve best possible vision. Various surgical procedures have been recommended to correct a CHP which is clinically predominant in one dimension of yaw (lateral rotation), pitch (anterior or posterior flexion/extension) or roll (lateral flexion). However, the presence of a complex CHP which is clinically evident in more than one dimension, warrants either a combination of multiple techniques or a stepwise approach. We report the case of a 26-year-old male with INS with an eccentric null and a multi-dimensional complex CHP of 30º left face turn, 20º right head tilt and 10º chin depression. The patient was managed by all four horizontal rectus muscle recession and resection with full tendon vertical transposition to address the face turn and head tilt. He underwent lateral rectus muscle (LR) recession with upward transposition and medial rectus muscle (MR) resection with downward transposition in the right eye. MR recession with upward transposition and LR resection with downward transposition were performed in the left eye. Postoperatively. the head posture improved significantly for both distance and near viewing. The chin depression also reduced after the procedure. He developed transient diplopia due to a small vertical deviation after the surgery, which was managed by prisms and fusional exercises. Thus, horizontal rectus muscle recession and resection combined with vertical transposition may be helpful to simultaneously improve the head tilt associated with the face turn, obviating the need for vertical rectus muscle or oblique muscle surgery.

The Developmental Eye Movement Test Does Not Detect Oculomotor Problems: Evidence from Children with Nystagmus

SIGNIFICANCE

The Developmental Eye Movement (DEM) test, a test purported to assess oculomotor skills, does not detect eye movement disorder in nystagmus syndromes. The test should not be used for the clinical evaluation of oculomotor disorders.

PURPOSE

The DEM test ratio compares a horizontal number naming subtest with a vertical one to identify oculomotor problems independent of a child's visual-verbal naming skills. Here, we tested the construct validity of this method by comparing scores of children with and without pathologic nystagmus. Such a nystagmus disturbs normal fixation and saccadic behavior because of the presence of involuntary rhythmic oscillations of the eyes. Therefore, if the ratio is indeed a comprehensive measure of oculomotor problems, children with nystagmus should show an increased ratio score.

METHODS

The DEM test performances of normally sighted children (n = 94), children with ocular visual impairments (VI o ; n = 33), and children with cerebral visual impairment (n = 30) were analyzed using linear regression. Part of the children with VI o and cerebral visual impairment had either fusion maldevelopment nystagmus syndrome (n = 8) or infantile nystagmus syndrome (n = 20), whereas the others showed no pathologic nystagmus.

RESULTS

The times needed for the horizontal and vertical subtests were significantly different between children with normal vision, VI o , and cerebral visual impairment ( P < .001). However, the presence of nystagmus did not add significantly to the horizontal and vertical times ( P > .20), nor did it have an effect on the ratio ( P > .10).

CONCLUSIONS

The DEM test ratio is not sensitive to fixation and saccade abnormalities associated with nystagmus, indicating that it does not have general construct validity to detect true eye movement disorders. Although not suitable for the evaluation of oculomotor disorders, the subtests do have clinical relevance in the diagnosis of cerebral visual impairment.

Investigating Determinants and Evaluating Deep Learning Training Approaches for Visual Acuity in Foveal Hypoplasia

Purpose

To describe the relationships between foveal structure and visual function in a cohort of individuals with foveal hypoplasia (FH) and to estimate FH grade and visual acuity using a deep learning classifier.

Design

Retrospective cohort study and experimental study.

Participants

A total of 201 patients with FH were evaluated at the National Eye Institute from 2004 to 2018.

Methods

Structural components of foveal OCT scans and corresponding clinical data were analyzed to assess their contributions to visual acuity. To automate FH scoring and visual acuity correlations, we evaluated the following 3 inputs for training a neural network predictor: (1) OCT scans, (2) OCT scans and metadata, and (3) real OCT scans and fake OCT scans created from a generative adversarial network.

Main Outcome Measures

The relationships between visual acuity outcomes and determinants, such as foveal morphology, nystagmus, and refractive error.

Results

The mean subject age was 24.4 years (range, 1–73 years; standard deviation = 18.25 years) at the time of OCT imaging. The mean best-corrected visual acuity (n = 398 eyes) was equivalent to a logarithm of the minimal angle of resolution (LogMAR) value of 0.75 (Snellen 20/115). Spherical equivalent refractive error (SER) ranged from −20.25 diopters (D) to +13.63 D with a median of +0.50 D. The presence of nystagmus and a high-LogMAR value showed a statistically significant relationship (P < 0.0001). The participants whose SER values were farther from plano demonstrated higher LogMAR values (n = 382 eyes). The proportion of patients with nystagmus increased with a higher FH grade. Variability in SER with grade 4 (range, −20.25 D to +13.00 D) compared with grade 1 (range, −8.88 D to +8.50 D) was statistically significant (P < 0.0001). Our neural network predictors reliably estimated the FH grading and visual acuity (correlation to true value > 0.85 and > 0.70, respectively) for a test cohort of 37 individuals (98 OCT scans). Training the predictor on real OCT scans with metadata and fake OCT scans improved the accuracy over the model trained on real OCT scans alone.

Conclusions

Nystagmus and foveal anatomy impact visual outcomes in patients with FH, and computational algorithms reliably estimate FH grading and visual acuity.

Prospective study of pediatric patients presenting with idiopathic infantile nystagmus-Management and molecular diagnostics

Idiopathic infantile nystagmus (IIN) is an inherited disorder occurring in the first 6 months of life, with no underlying retinal or neurological etiologies and is predominantly caused by mutations in the FRMD7 gene. IIN poses a diagnostic challenge as underlying pre-symptomatic "multisystem" disorders varying from benign to life-threatening should first be ruled out before nystagmus can be labeled as idiopathic. A multidisciplinary approach including multimodal ocular investigations and next-generation sequencing with whole-genome sequencing (WGS) or targeted gene panel testing is required to delineate the exact etiology. We report the clinical and genetic outcomes of 22 patients, from 22 unrelated families of diverse ethnicities, with IIN seen in the ocular genetics service at Moorfields Eye Hospital NHS Foundation Trust between 2016 and 2022. Thirty-six percent (8/22) received a confirmed molecular diagnosis with eight mutations identified in two genes (seven in FRMD7 including one novel variant c.706_707del; p. [Lys236Alafs*66], and one in GPR143). This study expands the mutational spectrum of IIN and highlights the significant role of an integrated care pathway and broader panel testing in excluding underlying pathologies.

Correlations of FRMD7 gene mutations with ocular oscillations

Mutations in the FERM domain containing 7 (FRMD7) gene have been proven to be responsible for infantile nystagmus (IN). The purpose of this study is to investigate FRMD7 gene mutations in patients with IN, and to evaluate the nystagmus intensity among patients with and without FRMD7 mutations. The affected males were subdivided into three groups according to whether or not having FRMD7 mutations and the types of mutations. Fifty-two mutations were detected in FRMD7 in 56 pedigrees and 34 sporadic patients with IN, including 28 novel and 24 previous reported mutations. The novel identified mutations further expand the spectrum of FRMD7 mutations. The parameters of nystagmus intensity and the patients’ best corrected visual acuity were not statistically different among the patients with and without identified FRMD7 mutations, and also not different among patients with different mutant types. The FERM-C domain, whose amino acids are encoded by exons 7, 8 and 9, could be the harbor region for most mutations. Loss-of-function is suggested to be the common molecular mechanism for the X-linked infantile nystagmus.

Pseudonystagmus in trochlear nerve palsy

We present the case report of a patient who presented with intermittent diplopia and left hypertropia associated with an apparent left superior oblique palsy. After dissociation with cover testing, he showed conjugate rhythmic vertical eye movements present in all gazes, thought to represent rapid rhythmically alternating fixation. The vertical rhythmic movement resolved after strabismus surgery.

CRB1-associated retinal dystrophy presenting as self-resolving opsoclonus and posterior uveitis

Purpose

To describe the unusual case of inflammatory CRB1-associated retinal dystrophy that initially presented with self-resolving opsoclonus.

Observations

We report the case of a now 2-year-old female who developed opsoclonus without myoclonus at the age of 4 months. An extensive workup for neuroblastoma and other systemic diseases was unremarkable, and all unusual eye movements self-resolved at age 10 months. Twenty-one months after initial presentation, she began having reduced visual behaviors, and comprehensive ophthalmic exam at that time revealed recurrent saccadic intrusions as well as severe, chronic retinal inflammation and dystrophic changes. An extensive infectious and inflammatory workup was negative. Genetic sequencing revealed two variants in CRB1: a heterozygous missense mutation and a heterozygous novel deletion involving exon 12. The patient was treated with monthly infliximab and methylprednisolone infusions with improvement in her optic disc and macular capillary leakage. The patient's 8-month-old sister also harbored the same variants in CRB1 and had early signs of retinal dystrophy and peripheral vascular leakage on exam.

Conclusion

Saccadic intrusions may be the first sign of a retinal dystrophy, and infants and children with this presentation should undergo a complete eye exam. We further highlight the link between CRB1-associated retinal dystrophy and inflammation, and how systemic steroids and tumor necrosis factor alpha (TNF-α) inhibitors may be effective therapies. Finally, we report a novel deletion in CRB1 that is likely highly penetrant.

Ophthalmological Manifestations of Oculocutaneous and Ocular Albinism: Current Perspectives

Albinism describes a heterogeneous group of genetically determined disorders characterized by disrupted synthesis of melanin and a range of developmental ocular abnormalities. The main ocular features common to both oculocutaneous albinism (OCA), and ocular albinism (OA) include reduced visual acuity, refractive errors, foveal hypoplasia, congenital nystagmus, iris and fundus hypopigmentation and visual pathway misrouting, but clinical signs vary and there is phenotypic overlap with other pathologies. This study reviews the prevalence, genetics and ocular manifestations of OCA and OA, including abnormal development of the optic chiasm. The role of visual electrophysiology in the detection of chiasmal dysfunction and visual pathway misrouting is emphasized, highlighting how age-associated changes in visual evoked potential (VEP) test results must be considered to enable accurate diagnosis, and illustrated further by the inclusion of novel VEP data in genetically confirmed cases. Differential diagnosis is considered in the context of suspected retinal and other disorders, including rare syndromes that may masquerade as albinism.

Abnormal Retinal Vessel Architecture in Albinism and Idiopathic Infantile Nystagmus

Purpose

Infantile nystagmus syndrome (INS) causes altered visual development and can be associated with abnormal retinal structure, to which vascular development of the retina is closely related. Abnormal retinal vasculature has previously been noted in albinism but not idiopathic infantile nystagmus. We compared the number and diameter of retinal vessels in participants with albinism (PWA) and idiopathic infantile nystagmus (PWIIN) with controls.

Methods

Fundus photography data from 24 PWA, 10 PWIIN, and 34 controls was analyzed using Automated Retinal Image Analyzer (ARIA) software on a field of analysis centered on the optic disc, the annulus of which extended between 4.2 mm and 8.4 mm in diameter.

Results

Compared with controls, the mean number of arterial branches was reduced by 24% in PWA (15.5 vs. 20.3, P < 0.001), and venous branches were reduced in both PWA (29%; 12.9 vs. 18.2, P < 0.001) and PWIIN (17%; 15.1 vs. 18.2, P = 0.024). PWA demonstrated 7% thinner "primary" (before branching) arteries (mean diameter: 75.39 µm vs. 80.88 µm, P = 0.043), and 13% thicker (after branching) "secondary" veins (66.72 µm vs. 59.01 µm in controls, P = 0.009).

Conclusions

PWA and PWIIN demonstrated reduced retinal vessel counts and arterial diameters compared with controls. These changes in the superficial retinal vascular network may be secondary to underdevelopment of the neuronal network, which guides vascular development and is also known to be disrupted in INS.

[Method of surgical treatment of patients with oculocutaneous albinism using artificial iris]

Oculocutaneous albinism is a group of autosomal recessive disorders that directly affect the hypopigmentation of the skin, hair, and eyes. According to the World Health Organization, albinism occurs in 1 out of 20 000 people in Europe and North America. Congenital changes in the organ of vision in albinism lead to a significant decrease in the visual functions of patients, worsening their quality of life.

PURPOSE

To study the results of surgical treatment with implantation of an artificial iris as a diaphragm element in patients with albinism.

MATERIAL AND METHODS

This article was based on the examination and treatment of 2 patients suffering from oculocutaneous albinism, which is characterized by hypopigmentation of the iris and retinal pigment epithelium of the retina, foveolar hypoplasia, low visual acuity, nystagmus, strabismus and excruciating photophobia. The patients were implanted an artificial iris in both eyes with fixation in the capsular bag in the first patient, and in the ciliary sulcus in the second.

RESULTS

In both patients, complaints of photophobia and optical phenomena have ceased. Visual acuity increased to 0.2 and remained without regression throughout the entire period of observation. Intraocular pressure and hydrodynamic parameters also remained stable throughout the observation period. The artificial irises were observed by ultrabiomicroscopy to remain in a stable position both when it was implanted in the capsule bag, and when it was seamlessly fixed in the ciliary sulcus.

CONCLUSION

The surgical interventions relieved patients from glare, at the same time improving visual acuity without correction, as well as achieving a pronounced cosmetic effect and visual rehabilitation. Artificial irises have proven to be a safe and effective way to treat patients with oculocutaneous albinism.

Eye movements elevate crowding in idiopathic infantile nystagmus syndrome

Idiopathic infantile nystagmus syndrome is a disorder characterised by involuntary eye movements, which leads to decreased acuity and visual function. One such function is visual crowding – a process whereby objects that are easily recognised in isolation become impaired by nearby flankers. Crowding typically occurs in the peripheral visual field, although elevations in foveal vision have been reported in congenital nystagmus, similar to those found with amblyopia. Here, we examine whether elevated foveal crowding with nystagmus is driven by similar mechanisms to those of amblyopia – long-term neural changes associated with a sensory deficit – or by the momentary displacement of the stimulus through nystagmus eye movements. A Landolt-C orientation identification task was used to measure threshold gap sizes with and without either horizontally or vertically placed Landolt-C flankers. We assume that a sensory deficit should give equivalent crowding in these two dimensions, whereas an origin in eye movements should give stronger crowding with horizontal flankers given the predominantly horizontal eye movements of nystagmus. We observe elevations in nystagmic crowding that are above crowding in typical vision but below that of amblyopia. Consistent with an origin in eye movements, elevations were stronger with horizontal than vertical flankers in nystagmus, but not in typical or amblyopic vision. We further demonstrate the same horizontal elongation in typical vision with stimulus movement that simulates nystagmus. Consequently, we propose that the origin of nystagmic crowding lies in the eye movements, either through image smear of the target and flanker elements or through relocation of the stimulus into the peripheral retina.

Development of multisensory integration following prolonged early-onset visual deprivation

Adult humans make effortless use of multisensory signals and typically integrate them in an optimal fashion.¹ This remarkable ability takes many years for normally sighted children to develop.^2,3 Would individuals born blind or with extremely low vision still be able to develop multisensory integration later in life when surgically treated for sight restoration? Late acquisition of such capability would be a vivid example of the brain's ability to retain high levels of plasticity. We studied the development of multisensory integration in individuals suffering from congenital dense bilateral cataract, surgically treated years after birth. We assessed cataract-treated individuals' reliance on their restored visual abilities when estimating the size of an object simultaneously explored by touch. Within weeks to months after surgery, when combining information from vision and touch, they developed a multisensory weighting behavior similar to matched typically sighted controls. Next, we tested whether cataract-treated individuals benefited from integrating vision with touch by increasing the precision of size estimates, as it occurs when integrating signals in a statistically optimal fashion.¹ For participants retested multiple times, such a benefit developed within months after surgery to levels of precision indistinguishable from optimal behavior. To summarize, the development of multisensory integration does not merely depend on age, but requires extensive multisensory experience with the world, rendered possible by the improved post-surgical visual acuity. We conclude that early exposure to multisensory signals is not essential for the development of multisensory integration, which can still be acquired even after many years of visual deprivation.

Genotype-Phenotype of Isolated Foveal Hypoplasia in a Large Cohort: Minor Iris Changes as an Indicator of PAX6 Involvement

Purpose

Foveal hypoplasia (FVH) is defined as the lack of fovea with a relatively preserved neuroretina, occurring either as an isolated FVH (IFVH) condition or associated with other diseases. This study aimed to systemically molecularly characterize IFVH.

Methods

Genetic defects in 33 families with IFVH were analyzed by exome sequencing. Variants in three genes (PAX6, SLC38A8, and AHR) were selected and evaluated with multistep bioinformatic tools.

Results

Mutations in the three genes were identified in 69.7% (23/33) of families with IFVH and infantile nystagmus, including 18 families with PAX6 mutations, 5 with SLC38A8 mutations, but none with AHR mutations. Clinical data from 32 patients in the 23 families showed FVH, infantile nystagmus, and full iris. Careful follow-up visits revealed subtle changes in iris in 9 of 14 patients with PAX6 variants. The PAX6 variants of the 18 families (15 missense and one stop-loss) were mostly located in the C-terminal region of the paired box domain. Variants in AHR, SLC38A8, and PAX6 contributed to IFVH in one (2%), 25 (45%), and 30 (53%) families with identified genetic defects (23 families in this study and 33 reported previously), respectively.

Conclusions

PAX6 and SLC38A8 mutations are the main cause of IFVH based on our data and a systematic review. IFVH-associated PAX6 variants are mostly missense with a specific location, indicating a specific correlation of these variants with IFVH but not with typical aniridia. Full iris with subtle structural abnormalities is more common in patients with PAX6-associated IFVH, suggesting a potential diagnostic indicator.

Reporting on Australian childhood visual impairment: the first 10 years

BACKGROUND

Visual impairment is rare but has significant impact on the neurobehavioural development and quality of life of children. This paper presents the key findings from the Australian Childhood Vision Impairment Register, which commenced in 2008 to report on children diagnosed with permanent visual impairment.

SUBJECTS/METHODS

Families consent to completing a data form related to their child and for contact with the child's ophthalmologist. Ophthalmologists complete and return a comprehensive data form on the child's primary and secondary ocular diagnoses, associated disabilities and health conditions, visual acuity and visual fields. Data is stored on a secure database and anonymised data is available to researchers and for planning purposes.

RESULTS

Nine-hundred four children and their families provided informed consent for participation, with 57% males and 43% females. Most children spoke English in their home. Eighty-three percent of children were born full term, with a birth weight of >2500 g (81%). Children were commonly suspected to have visual impairment by a parent, with 68% of families receiving a diagnosis of visual impairment by their child's first birthday. The most common primary diagnoses were retinal dystrophy (17%), CVI (15%) and Albinism (11%). A secondary diagnosis of infantile nystagmus occurred in 33% of children. Additional disabilities and/or developmental delay were reported for 44% of children. Corrected binocular visual acuity was reported for 75% of children, with moderate visual impairment being most common.

CONCLUSIONS

These findings contribute to knowledge of rare diseases affecting the eye and visual pathway and represent Australian childhood visual impairment.