Contrary to the classic description, the majority of posterior zonular fibers are not attached directly to the posterior lens capsule, but are anchored to the anterior hyaloid membrane on their path from the ciliary body to the posterior capsule. This finding is in good agreement with several previous observations and models that suggest support of the posterior lens surface during 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 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.

The goal of this protocol is to mimic the biomechanics of physiological accommodation in a cost-efficient, practical manner. Accommodation is achieved through the contraction of the ciliary body and relaxation of zonule fibers, which results in the thickening of the lens necessary for near vision. Here, we present a novel, simple method in which accommodation is replicated by tensing the zonules connected to the lens capsule via a manual lens stretcher (MLS). This method monitors the radial stretching achieved by a lens when subjected to a consistent force and allows for a comparison of accommodating lenses, which can be stretched, to non-accommodating lenses, which cannot be stretched. Importantly, the stretcher couples to the zonules directly, and not to the sclera of the eye, thus only requiring the lens, zonules, and ciliary body rather than the entire globe sample. This difference can significantly decrease the cost of acquiring donor cadaver lenses by about 62% compared to acquiring an entire globe.

PurposeTo characterize the peripheral defocus of the monkey crystalline lens and its changes with accommodation.MethodsExperiments were performed on 15 lenses from 11 cynomolgus monkey eyes (age: 3.8–12.4 years, postmortem time: 33.5 ± 15.3 hours). The tissue was mounted in a motorized lens stretcher to allow for measurements of the lens in the accommodated (unstretched) and unaccommodated (stretched) states. A custom-built combined laser ray tracing and optical coherence tomography system was used to measure the paraxial on-axis and off-axis lens power for delivery angles ranging from −20° to +20° (in air). For each delivery angle, peripheral defocus was quantified as the difference between paraxial off-axis and on-axis power. The peripheral defocus of the lens was compared in the unstretched and stretched states.ResultsOn average, the paraxial on-axis lens power was 52.0 ± 3.4 D in the unstretched state and 32.5 ± 5.1 D in the stretched state. In both states, the lens power increased with increasing delivery angle. From 0° to +20°, the relative peripheral lens power increased by 10.7 ± 1.4 D in the unstretched state and 7.5 ± 1.6 D in the stretched state. The change in field curvature with accommodation was statistically significant (P < 0.001), indicating that the unstretched (accommodated) lens has greater curvature or relative peripheral power.ConclusionsThe cynomolgus monkey lens has significant accommodation-dependent curvature of field, which suggests that the lens asserts a significant contribution to the peripheral optical performance of the eye that also varies with the state of accommodation.

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