Pupil location under mesopic, photopic, and pharmacologically dilated conditions.

PURPOSE To determine whether there are systematic changes in pupil location with changes in the state of pupil size and with other ocular variables. METHODS High-resolution images of the pupil of the eyes of 70 subjects were taken using an infrared-sensitive camera. Images were obtained under mesopic, photopic, and pharmacologically dilated conditions. From the images, the center and diameter of the corneal limbus and the pupil were computed. In addition, the location of the first Purkinje image was calculated. RESULTS The pupil center shifted consistently temporally as the pupil dilated. The total motion was relatively small, with a mean distance of 0.133 mm motion between the mesopic and photopic conditions, with the pupil diameter changing from 6.3 to 4.1 mm. Ninety percent of the subjects had a motion of less than 0.3 mm. One patient showed a motion of almost 0.6 mm. The change in location of the pupil center was not significantly related to refractive error, age, or the change of pupil diameter. CONCLUSIONS Changes in the location of the pupil center with changes in the dilation of the pupil are typically slight, but can be significant in a few subjects, especially in pharmacologically dilated pupils.