Abstract
Abstract: :
Purpose:Accommodation is based on a change in the shape of the crystalline lens. However, does the slackening of the zonules that induces this shape change also cause a change in the lateral position or tilt of the lens? This question is important since changes in lens position may underlie the changes in wavefront aberrations that have been shown to occur with accommodation (He et al, 2000). Wavefront aberrations may be important since they have been related to the development of childhood myopia (He et al, 2002). Methods:Nine young adults between the ages of 22 and 26 years were tested using the Canon AUTOREF R-1. This instrument provides two infrared light sources 20° to either side of the pupillary center that allow for the recording of Purkinje images almost simultaneously with accommodation and pupil size. Three computer images showing the position of the 1st ,3rd, and 4th Purkinje images within the pupil were recorded for each eye during each viewing condition. From these images, angle lambda, lens decentration and lens tilt relative to the pupillary axis were calculated (Barry et al, 1997). Subjects viewed targets at 0.25m, 0.33m, and 4.5m in the straight ahead position and 5° up, down, right, and left of straight ahead. Results:Angle lambda had a mean value of 2.43° ± 2.30° horizontally and 0.82° ± 0.94° vertically at distance and varied little with accommodation. The lens tilted 3.40° ± 2.18° horizontally and 2.07° ± 0.69° vertically in the opposite direction (slightly nasal and down) relative to the pupillary axis during distant viewing. During accommodation to 25 cm, horizontal tilt decreased significantly while vertical tilt changed little. The tilt change was highly significant for some individual eyes. Lateral displacement was an insignificant factor horizontally (-0.15 ± 0.10 mm) and vertically (0.06 ± 0.07 mm) at distance and did not change with accommodation. Conclusions:: Crystalline lens tilt partially compensates for the effects of angle lambda on wavefront aberrations thereby reducing them. Lens tilt changes significantly during accommodation, and this change can be large for some individuals. Lens tilt changes must induce wavefront aberration changes. The lateral position of the lens is well aligned with the pupillary axis and remains rigidly in position during accommodation. Supported by NIH Training Grant EY07149 and the New England College of Optometry Research Fund