Development and characterization of a mechanical compression device for quantifying the elasticity of the porcine and human crystalline lens

Abstract

PurposeWe present the development and characterization of an electromechanical device that quantifies the elasticity of the crystalline lens ex vivo by measuring its reaction force when it is compressed by a rod moved step by step. Our specifications required a robust system, fast to allow serial analysis, capable of measurements on an immersed lens, and highly resolved to detect small changes in elasticity.MethodsA first simple manual device was constructed to dimension the measuring system. The lenses (human and porcine) immersed in a buffer solution were placed on a precision weighing balance and compressed from top to bottom by a rod mounted on a micrometer screw. This system made it possible to define, among other things, the resolution of the balance (1 mg, 0.01 milli‐Newton). In a second device, the rod system was motorized with a resolution of 0.625 µm pitch in order to automate the measurement, and the balance data were integrated in real time into software executable on a desktop computer. A control camera (30 µm/pixel) was added to facilitate the approach of the rod in contact with the lens and to document the deformation experienced.ResultsThe built‐in calibration of the balance allows direct measurement in Newton. The device allowed determining the very homogeneous behavior of the lens (elastic reaction versus displacement) as well as the breaking point of the capsule which is much higher than the elastic deformation (at about 100 times the weight of the lens). Automation also allows the measurement of lens relaxation times during pulsed stimulation, for example by compression/decompression of 1 mm on a porcine lens.ConclusionsWith a measured effective fidelity of 5 µm and 0.01 mN, this direct compression system allows the mechanical elastrometry of the lens. The measurement of a large series of human and porcine lenses of different ages is in progress to determine its accuracy and repeatability. It will be useful for any research on lens biomechanics.