Simulating the Mechanics of Lens Accommodation via a Manual Lens Stretcher

Summary

We present an efficient method of studying lens accommodation by using a manual lens stretcher. The protocol mimics physiological accommodation by pulling the zonules connected around the lens capsule, thereby, stretching the lens.

Abstract

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.

Introduction

Accommodation is the process by which the human eye is able to dynamically adjust the shape of its crystalline lens to see objects at far or close distances in sharp focus. Accommodation is an intrinsically biomechanical process. Upon neural stimulus, the ciliary muscles produce a force onto the ciliary body and to the zonule fibers that attach to the circumference of the lens capsule^1,2. While there are different theories behind the biomechanics of accommodation, the most widely accepted is the Helmholtz hypothesis. According to the hypothesis, the lens is in a natural stretched state, corresponding to the th....

Protocol

The following protocols are accepted under the University of Maryland's Institutional Animal Care and Use Committee as well as the Institutional Review Board. The protocols follow federal, state and local standards, and the guidelines set out by the University of Maryland Policy on Biosafety.

1. Dissection of Eye Sample

1. Obtain an eye sample from local slaughterhouse or tissue bank. If an entire eye globe is obtained, immediately extract the lens, attached zonules, and vitreous.
   ​NOTE: The specific details described below pertain to both porcine and human eyes.
   1. Using disinfected surgi....

Results

Porcine eyes, a common sample for studying presbyopia via lens stretching^4,15, were obtained, (n = 10) from a local slaughterhouse and this protocol was used to observe the accommodation ability of the lenses. Figure 5A shows the comparison of the porcine lens before and after stretching via the MLS. There was an average 0.19 ± 0.07 mm increase in lens radius when stretched (p

Discussion

We have devised a novel method to provide an accurate and efficient way of studying the accommodation ability of the lens by utilizing a dual-piece clamping mechanism to couple the stretcher to the sample. During accommodation, the lens relaxes, and the diameter decreases in response to relaxation of the zonular fibers^1,2,4,19. The method focuses on this phenomenon by clamping and controlling t.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Manual Lens Stretcher	Bioniko	MLS	Different animal species will require different shoe sizes
Porcine Eye Samples	George G. Ruppersberger; slaughterhouse	N/A	Whole eyeballs were obtained
Human Eye Samples	The National Disease Research Interchange	N/A	Posterior poles without corneas were ordered
Dissecting Scissors (5 1/2'' Straight)	Electron Microsopy Sciences	72960
Tissue Forceps (4 1/2'')	Electron Microsopy Sciences	72960
iPhone 6s	Apple	N/A	Any imaging system with ~0.1 mm resolution will work
Sodium Hypochorite	Clorox	Clorox Regular-Bleach	Any disinfectant will work