Effect of anterior zonule transection on the change in lens diameter and power in cynomolgus monkeys during simulated accommodation

Purpose. To quantify the role of anterior zonular tension on the optomechanical lens response during simulation of accommodation in primates. Methods. Postmortem cynomolgus monkey eyes (n = 14; age range, 3.0-11.5 years) were dissected leaving intact the lens, zonules, ciliary body, hyaloid membrane, anterior vitreous, and a scleral rim. The lens was mounted in a lens-stretching system and stretched radially in step-wise fashion. The load, and the lens diameter and power were measured at each step and the diameter-and power-load relationships were quantified. The anterior zonular fibers were then transected, and the experiment was repeated. The equatorial lens diameter and lens optical power before and after zonular transection were compared. RESULTS. Stretching increased the lens diameter by 0.25 ± 0.09 mm (median ± interquartile range) before and 0.25 ± 0.19 mm after zonular transection. Stretching decreased the lens power by 13.0 ± 6.5 D before and 10.6 ± 8.0 D after zonular transection. The load required to change the diameter of the lens by 1 mm decreased from 18.8 ± 10.7 g before to 15.0 ± 7.8 g after zonular transection. The absolute change in power per gram of loading decreased from 2.5 ± 1.1 before to 2.0 ± 1.2 D after zonular transection. CONCLUSIONS. The cynomolgus monkey lens retains a significant fraction of its accommodative ability after transection of the anterior zonules in simulated accommodation experiments.