Shruti Senthilkumar
Introduction
Down syndrome (DS), caused by full or partial trisomy 21, is the most common chromosomal disorder in the UK, with an estimated incidence of 1 in 1,000 live births (1). Beyond its cognitive and systemic phenotype, DS confers an increased burden of ophthalmologic morbidity.
Epidemiology
DS is associated with an increased risk of ocular anomalies compared to the general population. A recent UK systematic review and meta-analysis (2) synthesising 54 studies (n > 5,000 individuals) reported prevalence estimates that refractive errors are the most prevalent ophthalmological condition, affecting approximately 70% of individuals with DS in pooled estimates, with hyperopia, astigmatism, and anisometropia reported at rates substantially exceeding those in age-matched controls. Strabismus has a pooled prevalence of 31%.
Other manifestations include nystagmus (~13%), lens opacities (including congenital and age-related cataracts, ~14%), and keratoconus (~9%), although the reported frequency of keratoconus varies widely by study methodology, age, and ethnicity.
Additional features described in observational studies include nasolacrimal duct obstruction, blepharitis, glaucoma, and iris abnormalities such as Brushfield spots. (3) Overall, ophthalmic findings have been noted in over 80% of paediatric and adolescent cohorts. (3)
Epidemiological patterns also suggest that the prevalence and severity of certain conditions (e.g., cataracts and corneal abnormalities) tend to increase with age and may correlate with the degree of intellectual disability (2,4), highlighting the importance of early and regular ophthalmological screening and intervention in this population
Refractive Errors
Refractive errors affect up to 70% of the population with DS (5,8). Hyperopia predominates in childhood, while myopia may develop later, often accompanied by significant astigmatism. Failure of normal emmetropisation contributes to persistent ametropia, increasing the risk of amblyopia and impaired visual function. Early detection through cycloplegic refraction is crucial, and timely corrective lenses can mitigate developmental and functional visual deficits. Longitudinal ophthalmic monitoring is recommended due to dynamic refractive changes with age.
Strabismus and Binocular Vision
Strabismus occurs in 20–60% of children (9), with esotropia more common than exotropia. Impaired ocular alignment often coexists with refractive errors, exacerbating amblyopia risk. Binocular vision deficits, including reduced stereopsis and abnormal vergence, are frequent and may persist despite corrective measures. Management encompasses both surgical and non-surgical approaches, including strabismus surgery and prism correction, and should be guided by regular orthoptic assessment, particularly in early childhood.
Nystagmus
Nystagmus, both manifest and latent, occurs in approximately 10–13% of individuals with DS (10). Involuntary oscillatory eye movements arise from disrupted ocular motor control and delayed neurodevelopment, reflecting impaired central coordination and atypical maturation of the gaze-stabilising neural circuits. Management focuses on correcting underlying refractive errors, optimizing binocular function, and in select cases, surgical interventions to reduce abnormal ocular oscillations.
Corneal Abnormalities
Individuals with Down syndrome demonstrate intrinsic corneal stromal abnormalities, including reduced central corneal thickness, altered collagen organization, and steepened corneal curvature (6,11). These structural changes predispose to keratoconus, which occurs at rates up to 10 times higher than in the general population. Other anterior segment anomalies, such as epiblepharon and eyelid malposition, contribute to ocular surface irritation. (12) Early detection with corneal topography and pachymetry is essential for monitoring keratoconus progression and initiating interventions, such as rigid contact lenses or corneal cross-linking, to preserve vision.
Anterior Segment Abnormalities
Anterior segment anomalies in DS include Brushfield spots and congenital or early-onset cataracts. Cataracts occur at higher rates than in the general population, potentially resulting from impaired lens epithelial cell differentiation and oxidative stress. (7)
Posterior Segment Abnormalities
Posterior segment manifestations include optic nerve head anomalies, retinal vascular patterning irregularities, and foveal structural differences (13,14). They can contribute to reduced visual acuity and impaired contrast sensitivity. Evaluation should include dilated fundus examination, spectral-domain OCT, and widefield retinal imaging, particularly in older children and adults, to document anomalies and monitor for progressive changes or secondary pathology.
Eyelid and Adnexal Disorders
Eyelid and adnexal abnormalities, including epicanthal folds, blepharitis, ptosis, epiblepharon, and nasolacrimal duct obstruction, are prevalent in DS. (3) Epicanthal folds and upward slanting palpebral fissures are characteristic features. Epiblepharon may cause corneal irritation and recurrent keratitis. Nasolacrimal duct obstruction, occurring in up to 35% of children, can lead to chronic epiphora and recurrent infection. (15) Early recognition allows conservative or surgical management to prevent ocular surface compromise.
Glaucoma
Although rare, congenital and secondary glaucoma have been reported in DS (2,16). Structural angle anomalies or lens-induced glaucoma may occur, particularly in the presence of congenital cataract. Assessment should include applanation tonometry, gonioscopy, and anterior segment evaluation. Lifelong surveillance is recommended, with prompt medical or surgical intervention to preserve optic nerve integrity.
Conclusion
Visual impairment in Down syndrome arises from the cumulative effects of refractive errors, strabismus, cataracts, keratoconus, and other ocular anomalies. Reduced visual acuity can impact development, learning, mobility, and daily functioning. Early identification and correction of amblyogenic factors, surgical intervention for cataract or strabismus, and rehabilitation with visual aids are essential. Multidisciplinary care, involving ophthalmology, optometry, orthoptists, and educational support, optimises developmental outcomes. Given the dynamic nature of ocular pathology in DS, lifelong monitoring is imperative.
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