Genetic basis of congenital strabismus

Genome-Wide Association Study with Three Control Cohorts of Japanese Patients with Esotropia and Exotropia of Comitant Strabismus and Idiopathic Superior Oblique Muscle Palsy

Esotropia and exotropia in the entity of comitant strabismus are multifactorial diseases with both genetic and environmental backgrounds. Idiopathic superior oblique muscle palsy, as the predominant entity of non-comitant (paralytic) strabismus, also has a genetic background, as evidenced by varying degrees of muscle hypoplasia. A genome-wide association study (GWAS) was conducted of 711 Japanese patients with esotropia (n= 253), exotropia (n = 356), and idiopathic superior oblique muscle palsy (n = 102). The genotypes of single nucleotide polymorphisms (SNPs) were determined by Infinium Asian Screening Array. Three control cohorts from the Japanese population were used: two cohorts from BioBank Japan (BBJ) and the Nagahama Cohort. BBJ (180K) was genotyped by a different array, Illumina Infinium OmniExpressExome or HumanOmniExpress, while BBJ (ASA) and the Nagahama Cohort were genotyped by the same Asian array. After quality control of SNPs and individuals, common SNPs between the case cohort and the control cohort were chosen in the condition of genotyping by different arrays, while all SNPs genotyped by the same array were used for SNP imputation. The SNPs imputed with R-square values ≥ 0.3 were used to compare the case cohort of each entity or the combined entity with the control cohort. In comparison with BBJ (180K), the esotropia group and the exotropia group showed CDCA7 and HLA-F, respectively, as candidate genes at a significant level of p < 5 × 10-8, while the idiopathic superior oblique muscle palsy group showed DAB1 as a candidate gene which is involved in neuronal migration. DAB1 was also detected as a candidate in comparison with BBJ (ASA) and the Nagahama Cohort at a weak level of significance of p < 1 × 10-6. In comparison with BBJ (180K), RARB (retinoic acid receptor-β) was detected as a candidate at a significant level of p < 5 × 10-8 in the combined group of esotropia, exotropia, and idiopathic superior oblique muscle palsy. In conclusion, a series of GWASs with three different control cohorts would be an effective method with which to search for candidate genes for multifactorial diseases such as strabismus.

Halil Pasha's legacy as a Turkish painter: Esotropia or pseudoesotropia in "Yaşlı Halayık"

Introduction: Esotropia is a form of strabismus, a condition characterized by the misalignment of the eyes. Specifically, esotropia refers to inward deviation of one or both eyes. It can manifest at different ages, ranging from infancy to adulthood, and can have varying degrees of severity. The false appearance of esotropia in the alignment of the visual axes is what defines pseudoesotropia. Halil Pasha was a Turkish painter known for his contributions to the art scene during the late 19th and early 20th centuries. His artistic talent, coupled with his influential position as a statesman, allowed him to leave a lasting impact on the cultural landscape of the Ottoman Empire. Methods: In the present study, artistic depictions of esotropia or pseudoesotropia in Halil Pasha's "Yaşlı Halayık" were evaluated. A comprehensive literature review on strabismus in medicine and art was conducted. Results: "Yaşlı Halayık", translated as "Old Servant Woman", is one of the iconic paintings of Turkish art. It reflects the social dynamics and lifestyle of the time, offering a glimpse into the lives of women serving in Ottoman households. When we examine this painting as a physician, the first thing we notice is the old woman's eyes. An eye misalignment in the left eye of the old servant woman is noticed. Discussion: In medical humanities, which are addressed in medical education, medicine and art intersect with different perspectives and understandings. Although the evaluation of medical scenes in artworks seems to have been first observed by an art historian, today physicians and medical students need to examine artworks more carefully and develop their observational skills. Iconodiagnosis is the medical analysis of artworks that looks for clinical signs suggestive of medical disorders and diseases. The application of iconodiagnosis in medical education is an alternative and stimulating way to exercise students' observation skills; not only the physical examination of the patient is important, but also the information obtained from their posture, clothing, general demeanour and even physical aids.

Ophthalmologic diagnoses in youths with autism spectrum disorder: Prevalence and clinical correlates

Autism spectrum disorder (ASD) is associated with a high prevalence of visual dysfunction. This study aimed to investigate the rates of amblyopia, refractive errors, and strabismus, as well as their clinical correlates in ASD. This population-based matched-cohort study used data from the Taiwan National Health Insurance Research Database. A total of 3,551 youths with ASD and 35,510 non-autistic control participants matched by age and sex were included. All the participants were followed-up until they were 18 years old. The prevalence of amblyopia, refractive errors, and strabismus was compared between the ASD and control groups. Effect modifiers, including sex, ASD subgroup, and co-diagnosis of intelligence disability, were examined. Compared to the control group, youths with ASD had a significantly increased risk of amblyopia (adjusted odds ratio [aOR] = 1.75), anisometropia (aOR = 1.66), astigmatism (aOR = 1.51), hypermetropia (aOR = 2.08), exotropia (aOR = 2.86), and esotropia (aOR = 2.63), but a comparable likelihood of myopia according to age. Males with ASD had a significantly lower likelihood of exotropia, but a higher likelihood of myopia than females with ASD. The autism subgroup had a higher OR for hypermetropia, but a lower OR for myopia than the other ASD subgroups. ASD youths with intelligence disabilities demonstrated significantly higher ORs for amblyopia, hypermetropia, and all types of strabismus and lower OR for myopia than those without intelligence disabilities. In conclusion, the rates of amblyopia, refractive errors, and strabismus were higher in youths with ASD. Ocular abnormalities in youths with ASD require a comprehensive assessment and management.

Candidate Genes in Testing Strategies for Linkage Analysis and Bioinformatic Sorting of Whole Genome Sequencing Data in Three Small Japanese Families with Idiopathic Superior Oblique Muscle Palsy

Idiopathic superior oblique muscle palsy is a major type of paralytic, non-comitant strabismus and presents vertical and cyclo-torsional deviation of one eye against the other eye, with a large vertical fusion range and abnormal head posture such as head tilt. Genetic background is considered to play a role in its development, as patients with idiopathic superior oblique muscle palsy have varying degrees of muscle hypoplasia and, rarely, the complete absence of the muscle, that is, aplasia. In this study, whole genome sequencing was performed, and single nucleotide variations and short insertions/deletions (SNVs/InDels) were annotated in two patients each in three small families (six patients in total) with idiopathic superior oblique muscle palsy, in addition to three normal individuals in one family. At first, linkage analysis was carried out in the three families and SNVs/InDels in chromosomal loci with negative LOD scores were excluded. Next, SNVs/InDels shared by the six patients, but not by the three normal individuals, were chosen. SNVs/InDels were further narrowed down by choosing low-frequency (<1%) or non-registered SNVs/InDels in four databases for the Japanese population, and then by choosing SNVs/InDels with functional influence, leading to one candidate gene, SSTR5-AS1 in chromosome 16. The six patients were heterozygous for 13-nucleotide deletion in SSTR5-AS1, except for one homozygous patient, while the three normal individuals were wild type. Targeted polymerase chain reaction (PCR) and direct sequencing of PCR products confirmed the 13-nucleotide deletion in SSTR5-AS1. In the face of newly-registered SSTR5-AS1 13-nucleotide deletion at a higher frequency in a latest released database for the Japanese population, the skipping of low-frequency and non-registration sorting still resulted in only 13 candidate genes including SSTR5-AS1 as common variants. The skipping of linkage analysis also led to the same set of 13 candidate genes. Different testing strategies that consisted of linkage analysis and simple unintentional bioinformatics could reach candidate genes in three small families with idiopathic superior oblique muscle palsy.

Profile of infantile strabismus at a tertiary eye care center in India

Purpose

To study the profile, risk factors, and management outcomes of infantile strabismus at a tertiary eye care center.

Methods

We prospectively analyzed the data of infants (children less than 1 year of age) who presented at our institute from August 2018 to December 2019. We excluded infants who did not complete a minimum follow-up of 6 months. Detailed meticulous history based on a set of standardized questionnaires was obtained and a comprehensive ophthalmological examination of the child was performed. Data were collected regarding refractive error (astigmatism; myopia; hyperopia; anisometropia [<1.0 DS or >1.0 DS]; astigmatism [<1.0 DS or >1.0 DS]) and the type of strabismus.

Results

During this period, we saw 4,773 infants, out of which 123 infants were diagnosed to have infantile-onset strabismus (hospital prevalence of 2.6%). Boys and girls were equally affected. Sixty-two patients had esotropia, 37 had exotropia, 2 had hypotropia, and 22 had pseudo strabismus. Prematurity, hypermetropia, and anisometropia had increased odds of developing esotropia, whereas delivery by cesarean section, delayed cry at birth, infantile seizures, parental consanguinity, delayed development of milestones, and myopia had increased odds of developing exotropia. Twenty-nine patients underwent a surgical correction. The mean deviation at the first visit was 42.59 ± 15.40 PD and 8.25 ± 12.70 PD at the last visit. For all patients who underwent a squint surgery, the change in ocular deviation was clinically and statistically significant (P-value <0.0001, paired t-test).

Conclusion

The hospital prevalence of infantile strabismus in our cohort was found to be 2.6%. Our study suggests that esotropia is two-fold more common in our cohort as compared to exotropia. Further, our study highlights risk factors for the development of strabismus in infancy, which must be kept in mind and awareness must be created among pediatricians. Surgical correction should be considered early during the infantile period, because it may lead to promote the development of good binocular vision.

Subclinical markers of strabismus in children 5-18 years of age

PURPOSE

To report the prevalence of subclinical markers of strabismus from a community-based screening of children.

METHODS

A family history and ophthalmic examination (including six markers of strabismus: oblique muscle dysfunction, stereopsis <60 arcsec, monofixation, nasal-temporal pursuit asymmetry, dissociated strabismus, and anisometropia) were obtained from consecutive children, aged 5-18 years, in the local school system and the pediatric outpatient clinic of Mayo Clinic, Rochester, Minnesota.

RESULTS

A total of 1,000 children (498 males [49.8%]) were examined at a mean age of 10.6 years (range, 5-18.98). Of the 1,000, 57 (5.7%) had strabismus, and 130 (13%) had some form of phoria. Of the 943 children without strabismus, 103 (10.9%) had one or more of the six subclinical markers, including 43 (4.5%) with inferior oblique dysfunction, 37 (3.9%) with anisometropia, 34 (3.6%) with subnormal stereopsis, 6 (0.6%) with nasal-temporal pursuit asymmetry, 3 (0.3%) with monofixation, and none with dissociated strabismus. A subclinical marker of strabismus occurred in 20 (12.7%) of the 157 nontropic subjects who had a family history of either strabismus, amblyopia, or both and in 83 (10.6%) of the 786 nontropic children without a family history.

CONCLUSIONS

In this community-based screening of children, subclinical disorders of binocular vision occurred in 10%-13% of children without strabismus, of which inferior oblique muscle dysfunction, anisometropia, and subnormal stereopsis were most prevalent. Identifying these disorders among strabismic families may be useful in elucidating the genetic puzzle of childhood strabismus.

Childhood Onset Strabismus: A Neurotrophic Factor Hypothesis

Strabismus is a genetically heterogeneous disorder with complex molecular and neurophysiological causes. Evidence in the literature suggests a strong role for motor innervation in the etiology of strabismus, which connects central neural processes to the peripheral extraocular muscles. Current treatments of strabismus through surgery show that an inherent sensorimotor plasticity in the ocular motor system decreases the effectiveness of treatment, often driving eye alignment back toward its misaligned pre-surgical state by altering extraocular muscle tonus. There is recent interest in capitalizing on existing biological processes in extraocular muscles to overcome these compensatory mechanisms. Neurotrophins are trophic factors that regulate survival and development in neurons and muscle, including extraocular muscles. Local administration of neurotrophins to extraocular muscles partially reversed strabismus in an animal model of strabismus. The hypothesis is that sustained release of neurotrophins gives more time for the ocular motor system to adapt to a slow change in alignment in the desired direction. The effect of neurotrophins on extraocular muscles is complex, as different neurotrophic factors have diverse effects on extraocular muscle contraction profiles, patterns of innervation, and density of extraocular muscle precursor cells. Neurotrophic factors show promise as a therapeutic option for strabismus, which may help to improve treatment outcomes and offset devastating amblyopia and psychosocial effects of disease in strabismus patients.

Non-classical 1p36 deletion in a patient with Duane retraction syndrome: case report and literature review

Background

Monosomy of 1p36 is considered the most common terminal microdeletion syndrome. It is characterized by intellectual disability, growth retardation, seizures, congenital anomalies, and distinctive facial features that are absent when the deletion is proximal, beyond the 1p36.32 region. In patients with proximal deletions, little is known about the associated phenotype, since only a few cases have been reported in the literature. Ocular manifestations in patients with classical 1p36 monosomy are frequent and include strabismus, myopia, hypermetropia, and nystagmus. However, as of today only one patient with 1p36 deletion and Duane retraction syndrome (DRS) has been reported.

Case presentation

We describe a patient with intellectual disability, facial dysmorphism, and bilateral Duane retraction syndrome (DRS) type 1. Array CGH showed a 7.2 Mb de novo deletion from 1p36.31 to 1p36.21.

Discussion

Our patient displayed DRS, which is not part of the classical phenotype and is not a common clinical feature in 1p36 deletion syndrome; we hypothesized that this could be associated with the overlapping deletion between the distal and proximal 1p36 regions. DRS is one of the Congenital Cranial Dysinnervation Disorders, and a genetic basis for the syndrome has been extensively reported. The HES3 gene is located at 1p36.31 and could be associated with oculomotor alterations, including DRS, since this gene is involved in the development of the 3rd cranial nerve and the 6th cranial nerve’s nucleus. We propose that oculomotor anomalies, including DRS, could be related to proximal 1p36 deletion, warranting a detailed ophthalmologic evaluation of these patients.

Strabismus in Children With Intellectual Disability: Part of a Broader Motor Control Phenotype?

PURPOSE

Intellectual disability (ID) results from a heterogeneous group of disorders and affects 1% to 2% of children. ID frequently occurs in association with other clinical features such as seizures or malformations. We suspected that strabismus might also be unusually frequent in this population and that it might be associated with ID groups affecting motor control.

METHODS

We reviewed phenotypic descriptors, extracted from medical records, for a heterogeneous series of 222 probands with ID who had been enrolled in a study of clinical application of exome sequencing. We estimated the frequency of strabismus and other common clinical features and explored statistical associations between them. Data from Population Data British Columbia and Online Mendelian Inheritance in Man were also examined for confirmation of our observations.

RESULTS

Strabismus had a higher prevalence among probands with ID than in the general population (odds ratio = 5.46). Moreover, probands with both ID and strabismus were more likely to have problems affecting motor control than those with ID and no strabismus (odds ratio = 2.84). Hypotonia was one of the most common motor control subgroups affecting the ID probands, and a frequent co-occurrence of strabismus and hypotonia was also observed (odds ratio = 2.51) and supported by related gene literature review. There was no evidence for associations between strabismus and other frequent clinical features.

CONCLUSION

Strabismus is a frequent feature in individuals with ID. The frequent co-occurrence of strabismus and motor control phenotypes, in particular hypotonia, suggests that a common cerebellar mechanism or pathway may underlie these phenotypes.

Strabismus in Bronzino's paintings: a hallmark of a realistic painter?

The present article analyses eleven paintings of Bronzino, one of the major painters of the late Italian Mannerism, in which the sitters are portrayed with deviating eyes. The reasons why Bronzino may have included a truant eye in his subjects are herein discussed. We consider the 'wandering' eye as a hallmark of Bronzino's style. The inclusion of strabismus may be part of the Mannerism tendency of using exaggerated hallmarks but pursuing at the same time an increasing realism that was typical of the 15th and 16th century movements.

Birth Anomalies in Monozygotic and Dizygotic Twins: Results From the California Twin Registry

Background

Inherited factors and maternal behaviors are thought to play an important role in the etiology of several congenital malformations. Twin studies can offer additional evidence regarding the contribution of genetic and lifestyle factors to common birth anomalies, but few large-scale studies have been reported.

Methods

We included data from twins (20,803 pairs) from the population-based California Twin Program. We compared concordance in monozygotic (MZ) to dizygotic (DZ) twins for the following birth anomalies: clubfoot, oral cleft, spina bifida, muscular dystrophy, deafness, cerebral palsy, strabismus, and congenital heart defects. Each birth anomaly was also examined for the associations with birth characteristics (birthweight and birth order) and parental exposures (age, smoking, and parental education).

Results

The overall prevalence of any selected birth anomaly in California twins was 38 per 1,000 persons, with a slightly decreasing trend from 1957–1982. For pairwise concordance in 6,752 MZ and 7,326 like-sex DZ twin pairs, high MZ:DZ concordance ratios were observed for clubfoot (CR 5.91; P = 0.043) and strabismus (CR 2.52; P = 0.001). Among the total 20,803 pairs, parental smoking was significantly associated with risk of spina bifida (OR 3.48; 95% CI, 1.48–8.18) and strabismus (OR 1.61; 95% CI, 1.28–2.03). A significant quadratic trend of increasing risk for clubfoot, spina bifida, and strabismus was found when examining whether father smoked, mother smoked, or both parents smoked relative to non-smoking parents (P = 0.029, 0.026, and 0.0005, respectively).

Conclusions

Our results provide evidence for a multifactorial etiology underlying selected birth anomalies. Further research is needed to understand the biological mechanisms.

Amblyopia: New molecular/pharmacological and environmental approaches

Emerging technologies are now giving us unprecedented access to manipulate brain circuits, shedding new light on treatments for amblyopia. This research is identifying key circuit elements that control brain plasticity and highlight potential therapeutic targets to promote rewiring in the visual system during and beyond early life. Here, we explore how such recent advancements may guide future pharmacological, genetic, and behavioral approaches to treat amblyopia. We will discuss how animal research, which allows us to probe and tap into the underlying circuit and synaptic mechanisms, should best be used to guide therapeutic strategies. Uncovering cellular and molecular pathways that can be safely targeted to promote recovery may pave the way for effective new amblyopia treatments across the lifespan.

Ophthalmoplegia and Congenital Cranial Dysinnervation Disorders

Some forms of ophthalmoplegia are congenital and fall into the category of Congenital Cranial Dysinnervation Disorders (CCDDs). These disorders arise from a primary defect of cranial nucleus/nerve development or guidance. Many have substantial limitations of ocular motility with or without other associated features. The type and degree of ophthalmoplegia can be similar between CCDD subtypes as well as with non-congenital forms of ophthalmoplegia. Therefore diagnostic confirmation often requires neuro-imaging and/or genetic investigations. The clinician should consider this category in cases of ophthalmoplegia that are congenital and nonprogressive in nature.

Expression of schizophrenia biomarkers in extraocular muscles from patients with strabismus: an explanation for the link between exotropia and schizophrenia?

Recent studies have implicated exotropia as a risk factor for schizophrenia. We determined whether schizophrenia biomarkers have abnormal levels of expression in extraocular muscles from patients with strabismus and explored whether differences in gene expression between medial and lateral rectus muscles may explain the specific association of schizophrenia with exotropia but not esotropia. Samples from horizontal extraocular muscles were obtained during strabismus surgery and compared with age- and muscle type-matched normal muscles from organ donors. We used PCR arrays to identify differences in gene expression among 417 signaling molecules. We then focused on established schizophrenia-related growth factors, cytokines, and regulators of the extracellular matrix. Among 36 genes with significantly altered gene expression in dysfunctional horizontal rectus muscles, over one third were schizophrenia-related: CTGF, CXCR4, IL1B, IL10RA, MIF, MMP2, NPY1R, NRG1, NTRK2, SERPINA3, TIMP1, TIMP2, and TNF (adjusted p value ≤ 0.016667). By PCR array, expression of three of these genes was significantly different in medial rectus muscles, while eleven were significantly altered in lateral rectus muscles. Comparing baseline levels between muscle types, three schizophrenia-related genes (NPY1R, NTRK2, TIMP2) had lower levels of expression in medial rectus muscles. Despite the surprisingly large number of schizophrenia-related genes with altered gene expression levels in dysfunctional muscles, the lack of specificity for medial rectus muscles undermines a model of shared, region-specific gene expression abnormalities between exotropia and schizophrenia, but rather suggests consideration of the alternative model: that exotropia-induced aberrant early visual experiences may enable and/or contribute as a causative factor to the development of schizophrenia.

Genetic testing for inherited eye misalignment

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of genetic testing for Inherited eye misalignment (IEM). Forms of IEM associated with variations in the SALL4, CHN1, TUBB3 and KIF21A genes have autosomal dominant inheritance, whereas those associated with variations in the ROBO3, PHOX2A, HOXA1 and HOXB1 genes have autosomal recessive inheritance. The prevalence of MS is currently unknown. Diagnosis is based on clinical findings, family history, visual acuity testing and fundus examination. The genetic test is useful for confirming diagnosis, and for differential diagnosis, couple risk assessment and access to clinical trials.

MGST2 and WNT2 are candidate genes for comitant strabismus susceptibility in Japanese patients

BACKGROUND/AIM

Strabismus is a common condition with misalignment between two eyes that may lead to decrease of visual acuity, lack of binocularity, and diplopia. It is caused by heterogeneous environmental and genetic risk factors. Our previous research has identified new chromosomal susceptibility loci in 4q28.3 and 7q31.2 regions for comitant strabismus in Japanese families. We conducted a verification study by linkage analysis to narrow the chromosomal loci down to a single gene.

METHODS

From Japanese and U.S. databases, 24 rsSNPs and 233 rsSNPs were chosen from the 4q28.3 and 7q31.2 region, respectively, and were typed in 108 affected subjects and 96 unaffected subjects of 58 families with primary and non-syndromic comitant strabismus. Three major analytical methods were used: transmission disequilibrium test (TDT), TDT allowing for errors (TDTae), and linkage analysis under dominant and recessive inheritance.

RESULTS

The SNPs with significant P values in TDT and TDTae were located solely at the gene, microsomal glutathione S-transferase 2 (MGST2), on chromosome 4q28.3 locus. In contrast, significant SNPs were dispersed in a few genes, containing wingless-type MMTV integration site family member 2 (WNT2), on chromosome 7q31.2 locus. The distribution of significant SNPs on the 7q31.2 locus showed that only the ST7 to WNT2 region in the same big haplotype block contained significant SNPs for all three methods of linkage analysis.

CONCLUSIONS

This study suggests that MGST2 and WNT2 are potential candidates for comitant strabismus in Japanese population.

Clinical characteristics of sibling patients with comitant strabismus

AIM

To investigate the clinical characteristics of sibling patients with comitant strabismus.

METHODS

Sibling patients who were diagnosed with comitant strabismus from January 2005 to December 2014 were retrospectively reviewed. Factors including age, sex, types of strabismus, refractive errors, angle of deviation, and coexistence of other strabismus were analyzed.

RESULTS

A total of 62 patients (31 pairs of siblings) were included. Of these, 26 pairs had intermittent exotropia, 3 had accommodative esotropia, and 2 had infantile esotropia. There were no pairs with different subtypes of strabismus. The age at first visit was 3.7±2.6y and the mean follow-up period was 30.5±24.1mo. In siblings with intermittent exotropia, there was no difference in age of onset, age at operation, or refractive errors between the first and second-born children. The 20 (77%) pairs of siblings with exotropia showed more than 80% concordance of maximum angle of deviation during follow-up. In the 9 pairs in which both siblings had an operation, the final angle of deviation after the operation was 8.2±8.1 prism diopters (PD) in first-born children and 8.6±6.5 PD in second-born children.

CONCLUSION

The subtypes of strabismus are the same in all pairs of siblings and clinical characteristics of strabismus are similar between the first and second-born children. This similarity could be an indicator for the diagnosis of second-born children. Further prospective study including a larger number of sibling patients is needed.

Altered Protein Composition and Gene Expression in Strabismic Human Extraocular Muscles and Tendons

Purpose

To determine whether structural protein composition and expression of key regulatory genes are altered in strabismic human extraocular muscles.

Methods

Samples from strabismic horizontal extraocular muscles were obtained during strabismus surgery and compared with normal muscles from organ donors. We used proteomics, standard and customized PCR arrays, and microarrays to identify changes in major structural proteins and changes in gene expression. We focused on muscle and connective tissue and its control by enzymes, growth factors, and cytokines.

Results

Strabismic muscles showed downregulation of myosins, tropomyosins, troponins, and titin. Expression of collagens and regulators of collagen synthesis and degradation, the collagenase matrix metalloproteinase (MMP)2 and its inhibitors, tissue inhibitor of metalloproteinase (TIMP)1 and TIMP2, was upregulated, along with tumor necrosis factor (TNF), TNF receptors, and connective tissue growth factor (CTGF), as well as proteoglycans. Growth factors controlling extracellular matrix (ECM) were also upregulated. Among 410 signaling genes examined by PCR arrays, molecules with downregulation in the strabismic phenotype included GDNF, NRG1, and PAX7; CTGF, CXCR4, NPY1R, TNF, NTRK1, and NTRK2 were upregulated. Signaling molecules known to control extraocular muscle plasticity were predominantly expressed in the tendon rather than the muscle component. The two horizontal muscles, medial and lateral rectus, displayed similar changes in protein and gene expression, and no obvious effect of age.

Conclusions

Quantification of proteins and gene expression showed significant differences in the composition of extraocular muscles of strabismic patients with respect to important motor proteins, elements of the ECM, and connective tissue. Therefore, our study supports the emerging view that the molecular composition of strabismic muscles is substantially altered.

Clinical-Radiologic Correlation of Extraocular Eye Movement Disorders: Seeing beneath the Surface

Extraocular eye movement disorders are relatively common and may be a significant source of discomfort and morbidity for patients. The presence of restricted eye movement can be detected clinically with quick, easily performed, noninvasive maneuvers that assess medial, lateral, upward, and downward gaze. However, detecting the presence of ocular dysmotility may not be sufficient to pinpoint the exact cause of eye restriction. Imaging plays an important role in excluding, in some cases, and detecting, in others, a specific cause responsible for the clinical presentation. However, the radiologist should be aware that the imaging findings in many of these conditions when taken in isolation from the clinical history and symptoms are often nonspecific. Normal eye movements are directly controlled by the ocular motor cranial nerves (CN III, IV, and VI) in coordination with indirect input or sensory stimuli derived from other cranial nerves. Specific causes of ocular dysmotility can be localized to the cranial nerve nuclei in the brainstem, the cranial nerve pathways in the peripheral nervous system, and the extraocular muscles in the orbit, with disease at any of these sites manifesting clinically as an eye movement disorder. A thorough understanding of central nervous system anatomy, cranial nerve pathways, and orbital anatomy, as well as familiarity with patterns of eye movement restriction, are necessary for accurate detection of radiologic abnormalities that support a diagnostic source of the suspected extraocular movement disorder. ^©RSNA, 2016.

Origins of strabismus and loss of binocular vision

Strabismus is a frequent ocular disorder that develops early in life in humans. As a general rule, it is characterized by a misalignment of the visual axes which most often appears during the critical period of visual development. However other characteristics of strabismus may vary greatly among subjects, for example, being convergent or divergent, horizontal or vertical, with variable angles of deviation. Binocular vision may also vary greatly. Our main goal here is to develop the idea that such “polymorphy” reflects a wide variety in the possible origins of strabismus. We propose that strabismus must be considered as possibly resulting from abnormal genetic and/or acquired factors, anatomical and/or functional abnormalities, in the sensory and/or the motor systems, both peripherally and/or in the brain itself. We shall particularly develop the possible “central” origins of strabismus. Indeed, we are convinced that it is time now to open this “black box” in order to move forward. All of this will be developed on the basis of both presently available data in literature (including most recent data) and our own experience. Both data in biology and medicine will be referred to. Our conclusions will hopefully help ophthalmologists to better understand strabismus and to develop new therapeutic strategies in the future. Presently, physicians eliminate or limit the negative effects of such pathology both on the development of the visual system and visual perception through the use of optical correction and, in some cases, extraocular muscle surgery. To better circumscribe the problem of the origins of strabismus, including at a cerebral level, may improve its management, in particular with respect to binocular vision, through innovating tools by treating the pathology at the source.

Strabismus genetics across a spectrum of eye misalignment disorders

Eye misalignment, called strabismus, is amongst the most common phenotypes observed, occurring in up to 5% of individuals in a studied population. While misalignment is frequently observed in rare complex syndromes, the majority of strabismus cases are non-syndromic. Over the past decade, genes and pathways associated with syndromic forms of strabismus have emerged, but the genes contributing to non-syndromic strabismus remain elusive. Genetic testing for strabismus risk may allow for earlier diagnosis and treatment, as well as decreased frequency of surgery. We review human and model organism literature describing non-syndromic strabismus, including family, twin, linkage, and gene expression studies. Recent advances in the genetics of Duane retraction syndrome are considered, as relatives of those impacted show elevated familial rates of non-syndromic strabismus. As whole genome sequencing efforts are advancing for the discovery of the elusive strabismus genes, this overview is intended to support the interpretation of the new findings.

A genome scan conducted in a multigenerational pedigree with convergent strabismus supports a complex genetic determinism

A genome-wide linkage scan was conducted in a Northern-European multigenerational pedigree with nine of 40 related members affected with concomitant strabismus. Twenty-seven members of the pedigree including all affected individuals were genotyped using a SNP array interrogating > 300,000 common SNPs. We conducted parametric and non-parametric linkage analyses assuming segregation of an autosomal dominant mutation, yet allowing for incomplete penetrance and phenocopies. We detected two chromosome regions with near-suggestive evidence for linkage, respectively on chromosomes 8 and 18. The chromosome 8 linkage implied a penetrance of 0.80 and a rate of phenocopy of 0.11, while the chromosome 18 linkage implied a penetrance of 0.64 and a rate of phenocopy of 0. Our analysis excludes a simple genetic determinism of strabismus in this pedigree.

Binocular summation and other forms of non-dominant eye contribution in individuals with strabismic amblyopia during habitual viewing

BACKGROUND

Adults with amblyopia ('lazy eye'), long-standing strabismus (ocular misalignment) or both typically do not experience visual symptoms because the signal from weaker eye is given less weight than the signal from its fellow. Here we examine the contribution of the weaker eye of individuals with strabismus and amblyopia with both eyes open and with the deviating eye in its anomalous motor position.

METHODOLOGY/RESULTS

The task consisted of a blue-on-yellow detection task along a horizontal line across the central 50 degrees of the visual field. We compare the results obtained in ten individuals with strabismic amblyopia with ten visual normals. At each field location in each participant, we examined how the sensitivity exhibited under binocular conditions compared with sensitivity from four predictions, (i) a model of binocular summation, (ii) the average of the monocular sensitivities, (iii) dominant-eye sensitivity or (iv) non-dominant-eye sensitivity. The proportion of field locations for which the binocular summation model provided the best description of binocular sensitivity was similar in normals (50.6%) and amblyopes (48.2%). Average monocular sensitivity matched binocular sensitivity in 14.1% of amblyopes' field locations compared to 8.8% of normals'. Dominant-eye sensitivity explained sensitivity at 27.1% of field locations in amblyopes but 21.2% in normals. Non-dominant-eye sensitivity explained sensitivity at 10.6% of field locations in amblyopes but 19.4% in normals. Binocular summation provided the best description of the sensitivity profile in 6/10 amblyopes compared to 7/10 of normals. In three amblyopes, dominant-eye sensitivity most closely reflected binocular sensitivity (compared to two normals) and in the remaining amblyope, binocular sensitivity approximated to an average of the monocular sensitivities.

CONCLUSIONS

Our results suggest a strong positive contribution in habitual viewing from the non-dominant eye in strabismic amblyopes. This is consistent with evidence from other sources that binocular mechanisms are frequently intact in strabismic and amblyopic individuals.

Comitant strabismus: Perspectives, present and future

Comitant strabismus is a common condition affecting infants, children and adults. Its impact on the affected patient may be severe resulting in visual loss, lack of binocularity, diplopia, social stigma and multiple corrective surgeries within the affected individual's lifespan. It is therefore important that this prevalent disorder should be better understood. We review the current understanding of the demographics and what is known of the etiology, risk factors and genetics of strabismus. We stress the importance of careful clinical assessment in classifying strabismus, and the common pitfalls in the measurement and pre-operative sensory work-up of the strabismic patient. The fact strabismus is comitant does not indicate it is benign: acute onset of comitant esotropia may be a presenting sign of pontine or cerebellar tumor. Lastly, we review the impact of genetics on our understanding of strabismus. While the causes of many types of congenital incomitant strabismus have been elucidated through careful observation and genetic screening, the genetics of comitant strabismus are more complex and multifactorial. Only through careful study and recruitment of large groups of affected individuals and families can we start to answer the question: why is this group of patients pre-disposed to develop strabismus. Doing so will help identify patients at risk, to spare them from the significant morbidity associated with this common disorder.

The screening of visual impairment among preschool children in an urban population in Malaysia; the Kuching pediatric eye study: a cross sectional study

BACKGROUND

To screen for visual impairment in Malaysian preschool children.

METHODS

Visual screening was conducted in 400 preschool children aged 4 to 6 years. The screening involved two basic procedures; the distant visual acuity test using the Sheridan Gardiner chart and the depth perception test using the Langs stereoacuity test. Criteria for referral were a visual acuity of 6/12 or less in the better eye or a fail in the depth perception test.

RESULTS

The prevalence of visual impairment was 5% (95% confidence interval [CI] = 3.3, 7.6). Of the 400 preschool children screened, 20 of them failed the distant visual acuity test or the stereopsis test. Refractive errors were the most common cause of visual impairment (95%, 95% CI = 76.2, 98.8); myopic astigmatism was the commonest type of refractive error (63.2%, 95% CI = 40.8, 80.9).

CONCLUSION

The study is a small but important step in the effort to understand the problem of visual impairment among our preschool children. Our study showed that it is feasible to measure distant visual acuity and stereopsis in this age group.

Strabismus following implantable anterior intraocular lens surgery

Strabismus in adults is increasing and has recently become an important focus of attention due to the development of refractive surgery techniques. In this case, permanent strabismus developed in a woman with previous high myopia after implantable anterior intraocular lens surgery. An ophthalmologic examination revealed the presence of a lens which was placed slightly downward in relation to the center of visual axis in the anterior chambers and up-drawn pupils in both eyes. The prismatic effect due to lens decentration may be the main cause of strabismus. Therefore, we suggest precise intraocular lens insertion and placement technique during surgery as well as careful ophthalmologic assessment including cover/uncover tests in all candidates for refractive surgery and full ocular motility evaluation if there is any doubt about binocular issues.

Eye movement control and its disorders

We review the supranuclear control centers and pathways leading to individual cranial nerve nuclei in the brainstem. We discuss horizontal and vertical gaze and their abnormalities, and review the cranial nerves which subserve eye movements, III, IV, VI, including their clinical testing. We highlight the sites at which these nerves are clinically affected, which often result in characteristic associated features with neurological localizing value. Differential diagnoses of cranial nerve palsies including Duane and Möbius syndromes are also described. Lastly, we discuss the nature of childhood neuromuscular junction disorders such as myasthenia gravis, as well as disorders of the muscle itself (chronic progressive external ophthalmoplegia (CPEO), thyroid orbitopathy).

How to deal with diplopia

Diplopia is a frequent neuro-ophthalmologic symptom with diverse etiologies. This article describes elementary diagnostic tests and frequent causes of diplopia. Monocular diplopia persists when the other eye is closed and usually disappears when the patient looks through a pinhole. It is usually caused by errors in the optical media of the eye and has to be differentiated from spectacle-induced side effect and non-organic disorders. A sign of non-organic etiology is absence of change in image position when the head is tilted. Binocular diplopia disappears regardless of which eye is closed. Binocular diplopia occurs when the images of both eyes cannot be fused. The most frequent direct cause of diplopia is acquired strabismus. Knowledge of several specific types of strabismus enables efficient patient management. Congenital and decompensating strabismus like accommodative esotropia, pathophoria, strabismus surso- and deorsoadductorius, retraction syndrome, Brown's syndrome and esotropia in high myopia only need ophthalmologic treatment. Orbital injury, orbital tumor, ocular myositis, Graves orbitopathy and vascular disease usually require multidisciplinary management. Neurogenic paresis, superior oblique myokymia, ocular neuromyotonia, myasthenia, chronic progressive external ophthalmoplegia (CPEO), internuclear ophthalmoplegia (INO) and skew deviation require specific neurologic examination. Treatment of diplopia includes treatment of the fundamental disorder, monocular occlusion, prisms and strabismus surgery.

Heritability of strabismus: genetic influence is specific to eso-deviation and independent of refractive error

Strabismus represents a complex oculomotor disorder characterized by the deviation of one or both eyes and poor vision. A more sophisticated understanding of the genetic liability of strabismus is required to guide searches for associated molecular variants. In this classical twin study of 1,462 twin pairs, we examined the relative influence of genes and environment in comitant strabismus, and the degree to which these influences can be explained by factors in common with refractive error. Participants were examined for the presence of latent ('phoria') and manifest ('tropia') strabismus using cover-uncover and alternate cover tests. Two phenotypes were distinguished: eso-deviation (esophoria and esotropia) and exo-deviation (exophoria and exotropia). Structural equation modeling was subsequently employed to partition the observed phenotypic variation in the twin data into specific variance components. The prevalence of eso-deviation and exo-deviation was 8.6% and 20.7%, respectively. For eso-deviation, the polychoric correlation was significantly greater in monozygotic (MZ) (r = 0.65) compared to dizygotic (DZ) twin pairs (r = 0.33), suggesting a genetic role (p = .003). There was no significant difference in polychoric correlation between MZ (r = 0.55) and DZ twin pairs (r = 0.53) for exo-deviation (p = .86), implying that genetic factors do not play a significant role in the etiology of exo-deviation. The heritability of an eso-deviation was 0.64 (95% CI 0.50-0.75). The additive genetic correlation for eso-deviation and refractive error was 0.13 and the bivariate heritability (i.e., shared variance) was less than 1%, suggesting negligible shared genetic effect. This study documents a substantial heritability of 64% for eso-deviation, yet no corresponding heritability for exo-deviation, suggesting that the genetic contribution to strabismus may be specific to eso-deviation. Future studies are now needed to identify the genes associated with eso-deviation and unravel their mechanisms of action.

Phenotype-phenotype and genotype-phenotype correlations in patients with idiopathic superior oblique muscle palsy

Idiopathic superior oblique muscle palsy presents, as quantitative phenotypes, vertical deviation and cyclodeviation in eye alignment on clinical testing, and superior oblique muscle hypoplasia on imaging. We determined ARIX and PHOX2B polymorphisms as genotypes, and analyzed phenotype-phenotype and genotype-phenotype correlations in 37 patients with idiopathic superior oblique muscle palsy. Vertical deviations were measured at upright position of the head and head tilt for 30° to either side, and angles of objective excyclodeviations were determined by image analysis on fundus photographs. Cross-sectional areas of the superior oblique muscle near the eye globe-optic nerve junction were measured by image analysis on coronal sections of magnetic resonance imaging to calculate the paretic-side/normal-side ratios. Among the phenotypes, the increase in vertical deviations elicited by head tilt to the paretic side, the decrease in vertical deviations elicited by head tilt to the normal side and the difference of angles of objective excyclodeviations between the paretic side and normal side were significantly correlated inversely with the paretic-side/normal-side ratios of the cross-sectional areas of the muscle (r=-0.43 with P=0.0084, r=-0.34 with P=0.038, and r=-0.43 with P=0.009, respectively, n=37, Pearson's correlation test). Fifteen patients with ARIX and/or PHOX2B polymorphisms had significantly greater paretic-side/normal-side ratios of the muscle compared with 20 patients without the polymorphisms (P=0.017, n=35, Mann-Whitney U-test). The patients with ARIX and/or PHOX2B polymorphisms had less hypoplastic superior oblique muscles.

Congenital esotropia and the risk of mental illness by early adulthood

OBJECTIVE

The purpose of this study is to investigate whether children with congenital esotropia (CET) are more likely than controls to develop mental illness by early adulthood.

DESIGN

Retrospective, population-based cohort.

PARTICIPANTS

Children (aged <19 years) diagnosed with CET while residing in Olmsted County, Minnesota, from January 1, 1965, to December 31, 1994, and their 1-to-1 non-strabismic birth- and gender-matched controls.

METHODS

The medical records of patients with esotropia and their controls were retrospectively reviewed for the subsequent development of psychiatric disease.

MAIN OUTCOME MEASURES

The development of mental illness and associated comorbidities among patients with CET and their controls.

RESULTS

A mental health disorder was diagnosed in 42 (33%) of the 127 patients with CET followed to a mean age of 20.4 years compared with 16% of controls (P = 0.002). Congenital esotropia increased the odds of developing a psychiatric illness 2.6 times (confidence interval, 1.5-4.8) compared with controls. The number of mental health diagnoses (P = 0.019) and the use of psychotropic medications (P = 0.015) were significantly more common among esotropic patients compared with non-strabismic controls.

CONCLUSIONS

Congenital esotropia, similar to those with intermittent exotropia or convergence insufficiency, increases the odds of developing mental illness by early adulthood 2.6 times compared with controls. The cause of this association does not seem to be associated with premature birth.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Congenital innervation dysgenesis syndrome (CID)/congenital cranial dysinnervation disorders (CCDDs)

Congenital loss of innervation to the extra-ocular muscles (EOMs) can have a profound effect on the target muscle. This has been well recognised in Duane's retraction syndrome. However, it has been less emphasised in other congenital oculo-motor disorders. Such congenital ocular motor defects have been expanded to include DRS, congenital fibrosis of EOMs, monocular elevation defect, Möbius syndrome, as well as several other non-ocular muscles supplied by cranial nerves such as facial muscles. Such loss of innervation to motor muscles can be unified as a defined clinical entity, which can be labelled as congenital innervation dysgenesis syndrome or CID for short. CID may also affect other muscles supplied by nerves other than the cranial nerves and may be sensory as well as motor.

The impact of pediatric vision disorders in adulthood

In addition to refractive errors such as myopia and astigmatism, ocular disorders that occur in infants, toddlers, and children may present lifelong problems for the child. Conditions such as strabismus, amblyopia, and retinopathy of prematurity may require adaptations in adulthood. In addition, vision disorders that occur in childhood may manifest as problems well into adulthood. When visual impairment is present, there may be further effects on overall health, self-perception, educational attainment, job choices, and a number of other social factors.

Germline Mosaicism for KIF21A Mutation (p.R954L) Mimicking Recessive Inheritance for Congenital Fibrosis of the Extraocular Muscles

OBJECTIVE

To document the genotype for familial congenital fibrosis of the extraocular muscles (CFEOM) with apparent autosomal recessive inheritance.

DESIGN

Interventional family study.

PARTICIPANTS

Two affected siblings, 3 asymptomatic siblings, and their 2 asymptomatic parents.

METHODS

Ophthalmologic examination and candidate gene analysis (KIF21A and PHOX2A from venous blood samples) of the 2 affected siblings and their parents; confirmatory testing for 3 available asymptomatic siblings.

MAIN OUTCOME MEASURES

Significant clinical observations and results of gene testing.

RESULTS

The 2 affected siblings had large-angle exotropia, moderate bilateral hypotropia, moderate bilateral ptosis, sluggish pupils, and almost complete ophthalmoloplegia with some abnormal synkinesis. The asymptomatic parents were not related and had unremarkable ophthalmic examinations. Four other siblings were normal by history; 3 underwent venous blood sampling for confirmatory testing. Candidate gene testing of PHOX2A, the gene for recessive CFEOM (CFEOM2), did not reveal mutation in the 2 patients or their parents. Sequencing of KIF21A, the gene for dominant CFEOM (CFEOM1), revealed heterozygous p.R954L in both affected individuals but in not in their parents or 3 asymptomatic siblings, consistent with parental germline mosaicism. Haplotype analysis suggested paternal inheritance but was not conclusive.

CONCLUSIONS

Parental germline mosaicism can mimic recessive inheritance in CFEOM and likely is underrecognized. Ophthalmologists should be aware of this phenomenon when counseling parents of children with apparent recessive (or de novo) hereditary eye disease. Unlike other reported KIF21A mutations that cause CFEOM1, the p.R954L variant seems to be associated with abnormal pupils.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Genetic and environmental contributions to strabismus and phoria: evidence from twins

The causes of manifest (strabismus) and latent (phoria) misalignment of the visual axes are incompletely understood. We calculated genetic and environmental contributions to strabismus based upon a critical review and quantitative meta-analysis of previous strabismus twin studies (n=3418 twin pairs) and calculated contributions to phoria based upon a new twin study (n=307 twin pairs). Our results suggest that genetic liability is necessary to develop strabismus, whereas environmental factors are sufficient to cause most phorias. The different etiologies implied by this work suggest that strabismus and phoria should be carefully distinguished in epidemiological work.

Transcriptional and functional differences in stem cell populations isolated from extraocular and limb muscles

The extraocular muscles (EOMs) are a distinct muscle group that displays an array of unique contractile, structural, and regenerative properties. They also have differential sensitivity to certain diseases and are enigmatically spared in Duchenne muscular dystrophy (DMD). The EOMs are so distinct from other skeletal muscles that the term "allotype" has been coined to highlight EOM group-specific properties. We hypothesized that increased and distinct stem cells may underlie the continual myogenesis noted in EOM. The side population (SP) stem cells were isolated and studied. EOMs had 15x higher SP cell content compared with limb muscles. Expression profiling revealed 348 transcripts that define the EOM-SP transcriptome. Over 92% of transcripts were SP specific, because they were absent in previous whole muscle microarray studies. Cultured EOM-SP cells revealed superior in vitro proliferative capacity. Finally, assays of the committed progenitors or satellite cells performed on myofibers isolated from EOM and limb muscles independently validated the increased proliferative capacity of these muscles. We suggest a model in which unique EOM stem cells contribute to the continual myogenesis noted in EOM and consistent with a role for their sparing in DMD. We believe the greater numbers of stem cells, their unique transcriptome, the greater proliferative capacity of EOM stem cells, and the greater number of satellite cells also offer clues for novel cell-based therapeutic strategies.

Genetic isolates in ophthalmic diseases

In recent years, noteworthy gains have been made in unravelling the genetic contribution to some complex ocular diseases, principally age-related macular degeneration. Yet, a relatively poor understanding of the genetic aetiology for many other heritable blinding diseases, such as glaucoma, keratoconus and myopia, remains. Genetic isolates, populations with varying degrees of geographical or cultural seclusion, provide an effective means for investigating the molecular mechanisms involved in human diseases. This is particularly true for rare diseases in which founded alleles can be rapidly driven to a high frequency due to restriction of gene flow in the population. Recent success in complex gene mapping has resulted from the widened linkage disequilibrium (LD) in the genome of genetically isolated populations. An improved understanding of the predisposing genetic risk factors allows for enhanced screening modalities and paves the foundations for the translation of genomic technology into the clinic. This review focuses on the role population isolates have had in the investigation of genes underlying complex eye diseases and discusses their likely usefulness given the expansion of large-scale case-control association studies.

Mental illness in young adults who had strabismus as children

OBJECTIVE

We investigated the prevalence and types of psychiatric disorders diagnosed by early adulthood among patients who had common forms of strabismus as children.

METHODS

The medical records of children (<19 years) who were diagnosed as having esotropia (N = 266) or exotropia (N = 141) while residents of Olmsted County, Minnesota, between January 1, 1985, and December 31, 1994, were reviewed retrospectively for psychiatric disease diagnoses. Each case subject was compared with a randomly selected, individually birth- and gender-matched, control subject from the same population.

RESULTS

A mental health disorder was diagnosed for 168 (41.3%) of the 407 patients with a history of childhood strabismus, who were monitored to a mean age of 17.4 years, compared with 125 control subjects (30.7%). Children with exotropia were 3.1 times more likely to develop a psychiatric disorder than were control subjects when monitored to a mean age of 20.3 years. Children with esotropia were no more likely to develop mental illness than were control subjects when monitored for similar periods. Patients with intermittent exotropia also were significantly more likely to have greater numbers of mental health disorders, mental health emergency department visits, and mental health hospitalizations and to have suicidal or homicidal ideation.

CONCLUSIONS

Children diagnosed as having strabismus in this population, especially those with exotropia, were at increased risk for developing mental illness by early adulthood. Patients with intermittent exotropia seemed to be particularly prone to developing significant psychiatric diseases by the third decade of life.

[Congenital cranial dysinnervation disorders]

Congenital cranial dysinnervation disorders (CCDDs) are responsible for 1-2% of infant strabismus cases. Insufficient innervation and misinnervation of aberrant nerve fibres lead to motility restrictions and synkinesis. We present the most common CCDDs and explain their pathogenesis and the resulting clinical features. Furthermore, we emphasize essential diagnostic steps and treatment aspects.