The aims of this study were a) to identify what constitutes visual disability resulting from glaucoma by means of a questionnaire developed for this purpose, b) to examine visual function in glaucoma using a wide range of psychophysical tests and c) to assess the relationship between objective visual function and patients' perception of their visual disability. The study was carried out in two phases. Firstly, a pilot questionnaire on visual disability in glaucoma was tested on 63 glaucoma patients. Results suggested that there were four main areas of difficulty in the daily life of glaucoma subjects: outdoor mobility, glare and lighting, household tasks and personal care. A significant correlation between self- reported disability and a measure of visual field loss was shown. The questionnaire was subsequently modified for the purpose of the main study and completed by 49 glaucoma subjects with various degrees of visual field loss and 20 normal controls. A range of psychophysical tests was carried out including automated perimetry, contrast sensitivity, critical flicker frequency, glare sensitivity, stereoacuity, colour perception and dark adaptation. Using factor analysis, the most frequently reported problems were grouped into the following five categories: central and near vision, peripheral vision, dark adaptation and glare, personal care and household tasks and outdoor mobility. These five factors accounted for 79% of the variability in the patients questionnaire responses. Fifteen questions related to the factors dark adaptation and glare, peripheral vision, outdoor mobility and central and near vision were found to be significantly correlated with the extent of visual field loss (p= 0.0001, r = -0.6) and could discriminate between patients and normals and also between groups with mild and severe visual field loss. Patients with moderate visual field loss did not experience significantly greater disability than patients with mild visual field loss (p= 0.08), although there was a trend towards significant difference. A strong relationship was found between the severity of visual field loss and all psychophysical tests (p<0.01), except colour vision. When comparing normals and early glaucoma patients, the best results were obtained for dark adaptation (p= 0.013), glare disability (p= 0.023) and the contrast sensitivity test (p= 0.039). When comparing objective visual function and self-reported visual disability, a strong relationship was found between the questionnaire performance index and all psychophysical tests (p <0.05), with the exception of colour vision. Glare disability (p<0.0001), contrast sensitivity (p <0.0001) and dark adaptation (p= 0.007) appear to be the tests that give the best information about quality of life issues. Glare disability, dark adaptation and contrast sensitivity appear to be the tests which give the best information about the quality of life in glaucoma. In addition these tests best separated early glaucoma from normal controls and deserve more attention in future research work on glaucoma.