US Patent 7625087 Pupillometers

Pupillometric apparatus for assessing pupillary near reflex in a subject incorporates a visible fixation point which is moveable between near and far positions and which is viewable through an eyepiece via an accomodation lens positioned between the eyepiece and the near position. The focal length of the accomodation lens exceeds the distance of the lens from both the near and far positions of the fixation point, so that the subject always observes virtual images in respect of the fixation point. In this way the distance between observed virtual positions of the fixation point at its near and far positions exceeds the actual distance between these positions.