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Suprathreshold Visual Function in Glaucoma
Bham, Habiba A.
Bham, Habiba A.
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Publication Date
2020
End of Embargo
Supervisor
Rights
The University of Bradford theses are licenced under a Creative Commons Licence.
Peer-Reviewed
Open Access status
Accepted for publication
Institution
University of Bradford
Department
School of Optometry and Vision Science. Faculty of Life Sciences
Awarded
2020
Embargo end date
Additional title
Abstract
Glaucoma is the leading cause of irreversible blindness worldwide but the effect
of glaucoma on patients’ vision under suprathreshold conditions relevant to their
natural visual environment is poorly understood. This project aimed to
investigate and further understand the effects of glaucoma on three aspects of
suprathreshold vision; apparent contrast of suprathreshold stimuli, detection
and discrimination of image blur and crowding of peripheral vision.
Psychophysical methods were employed to assess these three visual functions
by measuring contrast matches of Gabor stimuli, blur detection and
discrimination thresholds of edge stimuli and crowding ratios of Vernier targets.
These measures were obtained from glaucoma observers tested within and
outside of visual field defects and the data compared with healthy controls.
Contrast matching ratios were similar between glaucoma and healthy age similar controls despite sensitivity loss in the glaucoma group. Blur detection
and discrimination thresholds were similar between glaucoma observers’ tested
within and outside of visual field defects and age-similar controls, though
thresholds were slightly elevated for high contrast stimuli in the glaucoma visual
field defect group. Crowding ratios were similar between participants with
glaucoma and healthy young controls.
The results demonstrate that aspects of suprathreshold visual function can be
maintained in early glaucoma despite sensitivity loss at threshold. The results
provide empirical evidence as to the asymptomatic nature of the disease in its
early stages. It appears that in early glaucoma, there may be compensatory
mechanisms at work within the visual system under suprathreshold conditions
that can overcome loss of sensitivity at threshold.
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Type
Thesis
Qualification name
PhD