Understanding disability glare: the effects of scattered light on visual performance

Patterson, Emily (2015). Understanding disability glare: the effects of scattered light on visual performance. (Unpublished Doctoral thesis, City University London)

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Abstract

The focus of this thesis is on how light is scattered on its passage through the optics of the human eye, and the consequences for visual performance under different lighting conditions. A number of visual psychophysical measurement techniques were employed to investigate the impact of light scatter on various aspects of visual performance.

The preliminary experiments carried out were designed to explore the physical properties of scattered light in the eye. Scattered light varies in both amount and angular dependence, outcomes that relate directly to the number and size of particles involved. In this respect, scattered light is estimated using two methods: one that measures both the amount and the angular dependence of scattered light and the other that assumes constant angular dependence in all observers. The findings show that there are significant differences in angular dependence between observers and that the size of the differences correlates with errors in the estimation of the overall amount of scatter.

Experiments were then carried out to investigate the effects of increased scattered light on visual performance and whether these can explain any aspects of age-related visual degradation. To disentangle increased scattered light from the innumerable other changes that occur with ageing, the amount of scattered light in young, healthy eyes was increased using fogging filters. Increased scatter is shown to have only a small effect on chromatic sensitivity and the ability to recognise letters or other high contrast optotypes that are commonly used to assess visual acuity. Contrast sensitivity, on the other hand, can be much reduced in the presence of increased light scatter.

Item Type: Thesis (Doctoral)
Subjects: R Medicine > RE Ophthalmology
Divisions: School of Health Sciences > Department of Optometry & Visual Science
URI: http://openaccess.city.ac.uk/id/eprint/13651

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