Highlight
- More than 20% of parents of children with strabismus have strabismus themselves, highlighting strong familial aggregation.
- Over half of examined parents exhibit abnormal sensorimotor features, including decreased stereopsis and significant phorias.
- Low stereopsis in parents may represent a subclinical form of strabismus with genetic underpinnings.
- Clinical evaluations reveal discrepancies from self-reported diagnoses, emphasizing the need for thorough orthoptic examination in genetic studies.
Study Background
Strabismus, characterized by misalignment of the eyes, affects approximately 1–4% of children and can lead to significant visual impairment if untreated. It manifests as heterogeneous subtypes including infantile, accommodative, and non-accommodative esotropia as well as exotropia. Although environmental factors influence pathogenesis, familial aggregation suggests a genetic predisposition. However, the exact genetic mechanisms remain elusive due to phenotypic heterogeneity and under-recognition of subtle, subclinical forms. Previous research has indicated that parents of children with strabismus may demonstrate abnormal binocular vision metrics, such as reduced stereopsis, even in the absence of overt strabismus. Understanding the prevalence and spectrum of these features in parents could provide phenotypic markers critical for genetic linkage and association studies, furthering insights into inheritance patterns and potential targets for early identification and intervention.
Study Design
This prospective cohort study enrolled 2,164 parents of children diagnosed with various forms of strabismus at Boston Children’s Hospital, part of a larger genetics study. Of these, 481 parents (303 mothers and 178 fathers) underwent comprehensive orthoptic examinations assessing ocular alignment, binocular function, and stereopsis. Additionally, a retrospective review included 208 control children aged 8 years or older without visual complaints or strabismus history, establishing baseline stereopsis values. The main outcomes were the prevalence of strabismus, subnormal stereopsis (reflecting reduced depth perception), and significant phorias (latent eye deviations), defined as 10 prism diopters (PD) or greater. Self-reported survey data on strabismus diagnosis and treatment history supplemented clinical findings.
Key Findings
Examined parents of children with strabismus demonstrated high rates of abnormal sensorimotor function: 50.2% of mothers and 60.1% of fathers showed abnormal findings on orthoptic exam. Remarkably, 22.4% of mothers and 28.1% of fathers were clinically diagnosed with strabismus, a substantially higher prevalence than population estimates, confirming a strong familial predilection. Furthermore, 27.7% of mothers and 32.0% of fathers exhibited conditions associated with strabismus, including decreased stereopsis, phorias measuring 10 PD or more, or past treatments such as occlusion therapy or vision exercises indicative of binocular dysfunction.
Notably, the prevalence of abnormal parental findings did not significantly differ based on the strabismus subtype in the child, suggesting common underlying familial risk factors across strabismus phenotypes. Alignment studies demonstrated that parents and children frequently shared the same deviation type, underscoring phenotypic inheritance patterns.
In control children without strabismus, subnormal stereopsis was noted in 14.9%, a lower rate compared to parents of affected children, reinforcing the association between stereopsis deficits and familial risk.
The study also found a substantial discrepancy between self-reported strabismus diagnosis and clinically confirmed cases in parents, highlighting limitations of self-reporting and the importance of objective clinical assessment in research and practice.
Expert Commentary
This rigorous study robustly affirms the familial nature of strabismus, extending beyond overt misalignment to include decreased binocular visual function such as impaired stereopsis. The presence of subclinical phenotypes in parents may reflect incomplete penetrance or variable expressivity of strabismus-associated genetic variants. These findings emphasize that low stereopsis should be considered a relevant endophenotype in future genetic research rather than focusing solely on clinically manifest strabismus.
Clinically, awareness of high familial prevalence justifies screening parents of affected children and prompts detailed binocular vision assessments to detect subtle anomalies that may benefit from early intervention. However, while the study cohort was large, the examination subset represented only a portion of enrolled parents, which could introduce selection bias. Additionally, variability in clinical testing protocols and definitions of subnormal stereopsis across studies may affect generalizability.
Future genetic studies leveraging biobank data should incorporate quantitative binocular vision metrics, such as stereopsis thresholds, to better stratify phenotypes. Integrating these subclinical markers could improve the power to identify susceptibility loci and unravel biological pathways of strabismus.
Conclusion
This prospective cohort study highlights a markedly elevated prevalence of strabismus and decreased stereopsis in parents of children with strabismus, regardless of subtype. The findings reinforce the strong familial and likely genetic basis of strabismus and reveal that low stereopsis may serve as a subclinical phenotype. Discrepancies between self-reported and clinical diagnoses advocate for standardized orthoptic evaluation in both clinical and research settings. Incorporating stereopsis and binocular vision abnormalities into genetic studies promises to enhance understanding, early diagnosis, and possibly prevention strategies for strabismus, a common but genetically understudied ocular disorder.
Funding
Support was provided by Boston Children’s Hospital and associated research grants. Clinical trial registration details were not specified in the source publication.
References
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