Towards seeing clearly: the contribution of atypical optical structures to refractive error and accommodative function in Down syndrome

Abstract

Introduction:
Accommodation refers to the eye’s ability to focus on objects located at different distances through the adjustment of the refractive power of its crystalline lens. Accommodation dysfunction is common among individuals with Down syndrome; however, the factors contributing to that dysfunction remain unclear.

Aims and methods:
This thesis investigated the relationship between ocular structures and the accommodation response in typically developing individuals with different refractive errors (aged 18-30 years) and individuals with Down Syndrome (aged 7 to 30 years) compared to an age-and refractive error-matched typically developed control group to investigate the contribution of ocular structures to the variation in the accommodative response. The anterior segment structure in different accommodative states was investigated using CASIA2 Anterior Segment Optical Coherence Tomography, and simultaneous changes in accommodative response were measured using PowerRefractor3. Principal Component Analysis was used to investigate the relationships between different ocular structures and accommodation, and paraxial ray tracing was used for optical modelling of accommodation response.

Results:
There was a significant relationship between the eye's structure and accommodation. Individuals with different refractive errors exhibited different magnitudes of structural changes to produce a similar accommodative response. In Down Syndrome, the eye had an atypical structure with a thinner, flatter, and lower-powered crystalline lens, which was found to contribute less to the distribution of refractive errors. Individuals with Down Syndrome also had lower accommodative response and lesser accommodative structural changes compared to their typically developed peers, despite having similar ciliary muscle changes. The accommodative response in DS was significantly associated with baseline posterior lens curvature, with flatter curvature indicating a higher likelihood of a better response.

Conclusion:
There is a significant relationship between the shape of the eye’s optical structures and the accommodative response. This research reveals that in Down Syndrome, posterior lens curvature was significantly associated with the accommodative response and may indicate a structural limitation to accommodation in DS. This could arise from weaker lens capsule or increased lens stiffness.

Date of Award	Jun 2026
Original language	English
Sponsors	Department for the Economy & Vice Chancellor's Research Scholarship (VCRS)
Supervisor	Saugat Bhattacharyya (Supervisor), Kathryn Saunders (Supervisor), Julie-Anne Little (Supervisor) & Jose Manuel Gonzalez-Meijome (Supervisor)