The investigations described in this thesis have examined how, with particular reference to optical cues, the retinal image is analysed by the brain so as to generate the appropriate signals for controlling accommodation. This line of research involved behavioural studies on trained monkeys (Macaca mulatto), human psychophysical studies, mathematical analysis of the capabilities of visual neurons in detecting defocus and single unit studies in an anaesthetized preparation. The chromatic, temporal and binocular aspects of accommodation control were considered. CHROMATIC: The accuracy of accommodation in monkeys was found to be reduced in the absence of chromatic cues. The nature of the neural processing that might be involved in utilising chromatic cues to accommodation was investigated, both theoretically and electrophysiologically, and a specific neural model was constructed. TEMPORAL: The effects on human accommodation of varying the temporal parameters of simple grating stimuli were investigated. These experiments provided information about both the sensory mechanisms involved in accommodation control and the possible role of temporal cues to accommodation. The temporal variability of accommodation (and accommodative-vergence) were examined in the rhesus monkey. BINOCULAR: The nature of the binocular interactions in accommodation control were investigated, in both man and monkey, by presenting conflicting blur cues to the two eyes and recording the accommodation response. In the presence of such conflicting cues, the accommodative response was best described as a weighted average of the inputs to the two eyes. In addition to providing insights into the sensory guidance of accommodation, these studies have also permitted a detailed comparison of accommodative function in man and the rhesus monkey. There was a striking similarity between these two species in all areas studied; ie. role of chromatic cues, temporal variability and nature of binocular interactions. Thus the rhesus monkey appears to be an excellent experimental model for investigating the accommodation control system.