The nature and magnitude of the visual difficulties of five volunteer patients with severely contracted visual field and high visual acuities was investigated by several techniques. These comprised a questionnaire providing a quantitative score of visual impairment, a specially devised visual search task, and an arbitrary method of estimating visual efficiency. Many aspects of visual impairment resulting from contract visual fields were revealed and discussed. Performance scores on the search task indicated that the field expander would probably be useful to a small number of cases for continuous wear, usually as a binocular bioptic system. Other cases might benefit from a clip-on or hand-held device for occasional use. Methods of manufacture and dispensing and difficulty in locating suitable patients were the major limiting factors in this study. The methods of assessment, and the optical system described in this study are worthy of further investigation and development for trial on a larger number of patients.