City Research Online

Abstract

The primary aim of this study was to establish age-related, normal limits of monocular and binocular spatial vision under photopic and high mesopic conditions. Photopic and mesopic Visual Acuity (VA) and Functional Contrast Sensitivity (FCS) were measured with both positive and negative contrast optotypes under both binocular and monocular viewing conditions using the Acuity-Plus (AP) test. The experiments were carried out in normally sighted participants, aged 10 to 86 years. Data from participants who failed to meet pre-defined normal sight criteria were not included in the analysis. Mean and ±2.5σ were calculated for participants within 5-year subgroups. A biologically meaningful model was then fitted to these data. The Gauss-Newton method was used to calculate optimum, best-fit model parameters to predict mean values and upper and lower threshold limits for VA and FCS. These limits describe the effects of normal ageing on spatial vision for each of the 16 experimental conditions investigated. Out of the 382 participants recruited for this study, 285 participants passed the selection criteria for normal aging. Log transforms were applied to ensure approximate normal distributions. Outliers were also removed for each of the 16 stimulus conditions investigated based on the ±2.5σ limits criterion. The results show that under photopic conditions, the overall variability in results for both VA and FCS remained age-invariant up to ~50 years. A lower, age-invariant limit of ~ 30 years was more appropriate for the mesopic range with a gradual, but accelerating increase in both mean thresholds and inter-subject variability above this age. Binocular thresholds were smaller and much less variable when compared to either eye. This study has established upper normal, age limits for monocular and binocular viewing under photopic and high mesopic lighting conditions with both positive and negative contrast optotypes using a single test which can be implemented either in the clinic or in an occupational setting. Measurements of participants excluded from analysis due to systemic and/or ocular conditions were analysed separately and plotted against the newly established age-related normal limits of spatial vision in both lighting conditions. A substantial number of those excluded failed to meet the age-related normal limits established in the study. These preliminary findings suggest that the new age-related normal limits may turn out to be very useful in screening for systemic and ocular conditions in clinical practice.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RE Ophthalmology
Departments:	School of Health & Psychological Sciences > Optometry & Visual Sciences School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses Doctoral Theses

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