Partial sightedness is a sensory disability which can to some extent be alleviated by artificial aids. Many of the sensory methods used in robotics can be applied in attempts to recapture some of the sensory information a partially sighted person has lost. This paper describes a device which uses sonar and stereo vision sensors for this task. The device is portable, and is worn by the user, giving them freedom of movement over kerbs, stairs and rough ground. Sensor motion during walking is measured using visual egomotion recovery and odometry, and has been modelled to allow compensation in the sensor readings. A ground position estimate is continually updated by scene ground-plane fitting, or from the walk-motion model, and is used to classify scene features as obstacles or parts of the ground. Methods for the robust reconstruction of image points and lines into scene features are developed. The recognition of world objects of exceptional significance to a mobile person - kerbs and stairs - is given particular attention. A user interface, which has undergone limited real world testing, is also described. Experimental results are presented for the various parts of the system.