Abstract

The ambient light level determines largely the steady-state size of the pupil (Lowenstein et al, 1964) and rapid increments in light flux on the retina cause a brisk constriction of the pupil that is often described as the dynamic light reflex response (Alexandridis, 1985; Lowenfeld, 1993). The afferent pathways that control the steady-state size of the pupil and the dynamic light reflex response in man have been associated with subcortical projections and this is consistent with clinical observations which suggest that the pupils continue to respond normally to sudden changes in room illumination even when the patients are cortically blind (Brindley et al, 1969). It is of great interest to investigate whether the same afferent pathway controls both the steady-state and the dynamic light reflex response in man. Analysis of pupil response curves measured as a function of luminance contrast when long duration stimuli are employed suggests that two independent principal components are sufficient to account for the family of curves that describe the observed pupil responses. These components have been labelled sustained and transient (Young et al, 1993; Young & Kennis, 1993). A number of pupil studies have demonstrated the absence of Pupil Light Reflex (PLR) responses in patients with post-geniculate lesions when small test stimuli are employed (Harms, 1951; Cibis et al, 1975; Barbur et al, 1988; Kardon, 1992; Kardon et al, 1993). Such observations suggest that more than one afferent pathway is involved in the control of the pupil response to light and that these pathways may not be entirely subcortical. A better understanding of the visual pathways involved and the kind of visual stimulus characteristics that cause pupillary responses will undoubtedly increase the usefulness of pupil based tests in neurologic and ophthalmologic examinations. With this in mind we have developed background perturbation techniques (Cole et al, 1995) that attempt to isolate different components of the PLR response. Preliminary findings are reported in normal subjects and in a patient with optic nerve drusen. The results suggest that the PLR is driven by at least two components. One component that integrates light flux changes over large areas of the visual field and determines largely the size of the pupil and a second component that dominates the response when small stimuli are involved and contributes significantly to the dynamic PLR response. This component is likely to be absent in patients with post-geniculate lesions.

© 1996 Optical Society of America