What are the most salient visuoperceptual reading symptoms to identify visual stress in adults? Using exploratory factor analysis to develop the Ulster visual stress questionnaire.

Visual Stress (VS) is a reading disorder characterised by visuoperceptual distortion symptoms experienced when reading. VS diagnosis is on an ad-hoc basis, with symptomology and diagnostic criteria poorly understood. This study investigated reading symptoms in adults to develop a clinically useful questionnaire for VS diagnosis. A comprehensive 17-item questionnaire was developed probing reading symptoms derived from the existing literature. 1248 undergraduate students (aged 18-50 years) completed the questionnaire and pattern glare test. 294 participants (23.6 %) exhibited pattern glare (scores > 3 on a mid-spatial frequency pattern glare test) which was used as an indirect measure of cortical hyperexcitation. After exclusion of diagnosed migraineurs, data from 247 participants were analysed. Parallel analysis determined the number of distinct factors and exploratory factor analysis assigned symptoms to these factors. To ensure symptoms mapped to a single factor, retained items needed to satisfy three conditions: (i) load onto their primary factor if >0.40, (ii) cross-load onto alternative factors by <0.30 and (iii) exhibit a difference in item primary factor and subsequent factor loadings of >0.20. Five factors were identified and mapped well to aetiological theories proposed to explain visual stress: 1) Magnocellular Pathway Deficits 2) Cortical Hyperexcitability 3) Eye Movement/Tracking Issues 4) Aversion to High Temporal Frequency 'Flicker' and 5) Concurrent Pathologies associated with Visual Stress. Post-hoc item analysis reduced questionnaire content to ten items. Exploratory factor analysis enabled systematic creation of a robust 10-item questionnaire to aid visual stress diagnosis. The questionnaire will be applied in a clinical context and among different ages for validation purposes.