Accommodative facility as a predictor of ocular fatigue: A longitudinal and methodological analysis

Alfaifi, Khawlah 2025. Accommodative facility as a predictor of ocular fatigue: A longitudinal and methodological analysis. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Aim: This thesis investigated how temporal factors (time of day, week, and semester) and individual variability influence accommodative facility (AF) and ocular fatigue—measured using the Convergence Insufficiency Symptom Survey (CISS) and accommodative lag—while evaluating alternative AF methods to enhance clinical assessment. Background: AF is essential for visual performance and can be influenced by time-related factors and individual differences, such as symptom level. Despite its clinical significance, there is limited understanding of how these factors interact in the long-term and affect AF and CISS scores. Additionally, the effectiveness of different AF measurement methods remains underexplored. Methods: Two cohorts of undergraduate students (n = 90; varied across visits/tests) were assessed using longitudinal and cross-sectional designs. AF (number of cycles, NoC) and CISS scores were measured under varying temporal conditions. Subgroup comparisons were conducted for symptomatic vs. asymptomatic participants and for below-normal vs. withinnormal amplitude of accommodation (AA; Hofstetter). Three AF methods—standard symmetrical, asymmetrical (tonic-accommodation-scaled, TA-scaled), and amplitude-scaled (AA-scaled)—were compared for sensitivity, specificity, and ROC performance in distinguishing symptomatic participants. TA and accommodative lag were recorded using the PowerRefractor 3. Results: Semester timing significantly influenced both NoC and CISS, with increased AF performance and higher fatigue in the second semester, whereas time-of-day showed no effect and time-of-week effects were inconsistent between cohorts. Across visits, NoC showed a consistent negative association with CISS, indicating reduced AF with increasing fatigue. Accommodative lag demonstrated weak, non-significant associations with both CISS and NoC. Among AF methods, the AA-scaled approach showed the highest diagnostic accuracy for differentiating symptomatic from asymptomatic participants. Conclusion: The results highlight that AF and ocular fatigue vary across time and individual symptom levels, underscoring the need to account for temporal factors in clinical evaluation. The AA-scaled method proved the most effective for assessing AF and fatigue. Future work should integrate multiple accommodative components into a single AF test, develop a symptom measure specific to accommodative dysfunction, and distinguish visual fatigue from psychological or physical stress.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Optometry and Vision Sciences
Subjects:	R Medicine > RE Ophthalmology
Date of First Compliant Deposit:	24 February 2026
Last Modified:	24 Feb 2026 13:56
URI:	https://orca.cardiff.ac.uk/id/eprint/185086

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