IN-VIVO INCREASE OF THE HUMAN LENS EQUATORIAL DIAMETER DURING ACCOMMODATION

The movement of the human lens equator during accommodation was examin ed in vivo. High-resolution ultrasound images of the lens equator were obtained from young human subjects whose amplitude of accommodation w as controlled with 1% tropicamide and 2% pilocarpine. To avoid errors that otherwise arise from eye rotation or other movement, the cornea a nd sclera were used as positional references in comparative studies of the video images obtained from the unaccommodated and accommodated st ates. During accommodation, the movement at the lens equator involved small displacement; i.e., <100 mu m, and the equator did not move ante riorly or posteriorly but peripherally toward the sclera. These result s indicate that the lens equator is under increased zonular tension du ring accommodation, in contradiction to Helmholtz's widely accepted th eory of accommodation.