Visual field coordinates of pupillary circular axis and optical axis.

Abstract

We term the visual field position from which the pupil appears most nearly circular as the pupillary circular axis (PCAx). The aim was to determine and compare the horizontal and vertical coordinates of the PCAx and optical axis from pupil shape and refraction information for only the horizontal meridian of the visual field. The PCAx was determined from the changes with visual field angle in the ellipticity and orientation of pupil images out to ±90 degrees from fixation along the horizontal meridian for the right eyes of 30 people. This axis was compared with the optical axis determined from the changes in the astigmatic components of the refractions for field angles out to ±35 degrees in the same meridian. The mean estimated horizontal and vertical field coordinates of the PCAx were -5.3 (±1.9) and -3.2 (±1.5) degrees compared with -4.8 (±5.1) and -1.5 (±3.4) degrees for the optical axis, respectively. The vertical coordinates of the two axes were just significantly different (p = 0.03), but there was no significant correlation between them. Only the horizontal coordinate of the PCAx was significantly related to the refraction in the group. On average, the PCAx is displaced from the line-of-sight by about the same angle as the optical axis, but there is more intersubject variation in the position of the optical axis. When modeling the optical performance of the eye, it appears reasonable to assume that the pupil is circular when viewed along the line-of-sight.