The asymmetric nature of glaucoma suggests that a high proportion of persons with glaucoma will have an APD (although many may be subtle and would be missed with less refined testing methods). When glaucoma patients have severe nerve damage or when field loss is bilateral and symmetric, an APD may not be present or may be too small to detect. Noting this limitation, the investigators will compare pupillary responses to stimuli at different locations (for example the superior compared to the inferior hemifield) to determine whether the investigators can detect asymmetric glaucoma damage within the same eye. In addition, it is likely that the pupil response in glaucoma will be diminished when compared to normal, which will also help with detection.