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Abstract

Cataract commonly occurs in older adults and is associated with degraded vision, impaired mobility and increased risk of falls. Cataract surgery restores transparency of the optical media by replacing the natural lens with an artificial intraocular lens (IOL). Modern toric and aspheric IOLs can improve optical quality and refractive outcomes; yet their potential impact on dynamic balance and fall risk is not well understood. This thesis used an experimental research methodology to examine how controlled changes in visual quality, arising from simulated cataract and from differences in IOL design, toric alignment and aberration profile, influence dynamic stability and gaze behaviour, and how these findings can inform a clinically applicable trial framework.Chapters 2 to 4 used induced blur using Bangerter foils in healthy adults to model cataract-related visual degradation during three functional mobility tasks: the Timed Up and Go (TUG) test, level walking with an unexpected obstacle, and stair ascent and descent. Wearable inertial measurement units positioned at the trunk (L3) and head (Occiput/T1 spinous process), together with mobile eye-tracking, were used to quantify centre-of-mass (CoM) acceleration, jerk (as an index of smoothness), head kinematics and gaze behaviour. Across all tasks, blurred vision consistently increased mediolateral and vertical CoM acceleration and jerk, particularly during turning, obstacle negotiation and stair descent, while anteroposterior smoothness was relatively preserved. Participants adopted more flexed head posture and devoted longer and more frequent fixations to waypoints and hazards, indicating a shift towards higher-gain, less smooth control strategies when visual information was degraded.Chapters 5 and 6 present optical bench and modelling studies that evaluated how visual quality is altered by IOL design, toric alignment and decentration. Chapter 5 compared different systems for quantifying toric meridian alignment and demonstrated that fully automated, non-cornea-referenced analytical modes provided superior repeatability and agreement across IOL designs. Chapter 6 showed that optical performance of four monofocal IOLs is strongly influenced by decentration, with marked differences between spherical, neutral aberration, negative spherical aberration and compensatory designs. Chapter 7 synthesised these mechanistic and optical insights into a proposed NHS randomised controlled trial comparing toric and non-toric monofocal IOLs in patients with pre-existing corneal astigmatism, using axis-resolved CoM jerk, gaze metrics, fear of falling and cataract-related quality of life as key outcomes. Overall, this thesis provides new multi-level evidence linking IOL optics with dynamic stability and proposes an innovative multidisciplinary framework for evaluating cataract surgery as part of a broader falls-prevention and mobility-preservation strategy in older adults.

Awarding Institution(s)

University of Plymouth

Award Sponsors

Carl Zeiss SMT AG

Supervisor

Phillip Buckhurst, Hetal Buckhurst, Catriona MacLennan, Gary L. Shum

Document Type

Thesis

Publication Date

2026

Deposit Date

September 2026

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

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