Figure 1.
Purkinje reflections and eye tracking. (A) As it travels through the eye, an incident ray of light gets reflected by the structures that it encounters. The first and second Purkinje reflections (P1 and P2) result from the anterior and posterior surfaces of the cornea. The third and the fourth Purkinje reflections (P3 and P4) originate from the anterior and posterior surface of the lens. (B) An image of the Purkinje reflections captured with the prototype described in this article. P1 and P4 can be imaged simultaneously. Here P3 is out of focus, and P2 largely overlaps with P1. Note that P1 is larger and has a higher intensity than P4. (C) An example of eye-tracker that uses Purkinje reflections, the Generation V Dual Purkinje Eye-tracker (DPI) from Fourward Technologies. This optoelectronic device has mobile components that, when properly tuned, follow P1 and P4 as the eye rotates.