Effect of Anterior Zonule Transection on the Change in Lens Diameter and Power in Cynomolgus Monkeys during Simulated Accommodation

Abstract

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 ϭ 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 Ϯ 0.09 mm (median Ϯ interquartile range) before and 0.25 Ϯ 0.19 mm after zonular transection. Stretching decreased the lens power by 13.0 Ϯ 6.5 D before and 10.6 Ϯ 8.0 D after zonular transection. The load required to change the diameter of the lens by 1 mm decreased from 18.8 Ϯ 10.7 g before to 15.0 Ϯ 7.8 g after zonular transection. The absolute change in power per gram of loading decreased from 2.5 Ϯ 1.1 before to 2.0 Ϯ 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.

Influence of Shape and Gradient Refractive Index in the Accommodative Changes of Spherical Aberration in Nonhuman Primate Crystalline Lenses

“…Upon arrival at the laboratory, all eyes were either directly prepared for stretching experiments or refrigerated at 48C before testing. 54 The time between euthanasia and use was 11 6 14 (range, 1-48) hours in this study.…”

The Zonules Selectively Alter the Shape of the Lens During Accommodation Based on the Location of Their Anchorage Points

“…[13][14][15] The asymmetry in the anchorage points and orientation of the anterior and posterior zonular fibers has been investigated in primates using a lens stretcher and a selective anterior zonular transection procedure. 16 We found that a significant amount of accommodative ability remained after transection of the anterior zonular fibers, but the change in power for a given load was reduced. The changes in curvature of one or both of the anterior and posterior surfaces must therefore also have been altered following transection; but without curvature measurements, we could only speculate about the details.…”

A quantitative geometric mechanics lens model: Insights into the mechanisms of accommodation and presbyopia

“…In reality, the equatorial loading is distributed via a complex arrangement of zonular fibers. Removal of some of these fibers has been shown to alter the optical response of the lens, thereby demonstrating the importance of the distribution of loading about the equatorial region (Nankivil et al, 2009).…”