Comparison of different techniques to evaluate the biomechanics of the accommodative apparatus in human eyes

Purpose For the study of the biomechanical properties of lens and zonules in a stretching device, we wanted to investigate the effect of keeping the ciliary body intact or cutting it radially. Methods We studied the anterior eye segment of 3 pairs of presbyopic human donor eyes (ages 51-85). These segments, comprising of lens, zonules, ciliary body and sclera, were radially stretched in our device which allows force and tissue elongation measurements to be made. First, each pair (OD and OS) was stretched with the ciliary body intact and the lens in place, afterwards, in OD, the ciliary body was cut radially and the lens was kept, and in OS, the ciliary body was kept intact and the lens removed, then we stretched again. Forces are given at 500 µm stretch, measured from lens centre to ciliary body edge. Results The mean force with the ciliary body intact and the lens in place was 74 mN. When the ciliary body was cut (with lens in place) the required force was 35 mN. When the ciliary body was keep intact and the lens removed we measured a force of 47 mN, which represents the contribution of the circumferential stretch of the ciliary body. Conclusion Stretching anterior eye segments showed that the required forces were considerably higher when the ciliary body was kept intact as compared when it was cut radially. These forces were increased due to the circumferential resistance by the ciliary body.