The Mechanism of Accommodation in

We appreciate the thought and attention to detail by Glasser and Kaufman in confirming Helmholtz mechanism of ac-commodation. Controlling for eye movements and conver-gence makes such a study challenging and the authors have addressed this quite adequately. In 1994 we presented a dynamic study of accommoda-tion using ultrasound biomicroscopy (UBM) in which hu-man subjects were given an accommodative task while one eye was studied with UBM.1 We demonstrated a character-istic posterior bowing of the iris in the accommodative state which was most prominent in young individuals and pro-gressively less apparent with aging. Our findings suggested that this may be an active part of the accommodative pro-cess in humans, in addition to the classic Helmholtz mech-anism. In their current paper, Glasser and Kaufman site a ref-erence that removal of the iris reduces maximal accommo-dation achieved.2 They also mention that UBM findings in some noniridectomized monkeys were similar. This is sug-gestive to us that the iris does play a role in primate accommodation. In these times of refractive surgery and potential surgery for presbyopia, we think it is critical to understand all components of the mechanism of accommodation.3 Glasser and Kaufman’s paper is a substantial step forward in this direction. We are interested in the authors further comments in regard to the iris. Further studies may help determine whether the iris is important in the accommodative mecha-nism