Purpose Ex vivo measurement of the elastic properties of human lens zonules as a function of age in presbyopes. Methods We studied 16 presbyopic human donor eyes (ages 47 to 97). Anterior eye sections with crystalline lens, zonules, ciliary body and sclera were radially stretched. The stretching device consists of a chamber filled with balanced salt solution and eight radial hooks to hold the anterior eye section. Radial stretching was created with a stepper motor connected to a digital outside micrometer for linear displacement and digital balance for force measurement. Three eye globes were used to test our methodology. For 13 eye globes, the spring constant, elastic modulus of the zonular system, and Young's modulus of the zonules were calculated. Results We found linear dependence for force‐elongation and force‐strain relationships at all ages. In young presbyopic eyes (ages 47 to 60), the Young's modulus of the zonules was 340 mN/mm²; whereas in older eyes (ages 83 to 97), it was significantly lower at 270 mN/mm². However, the correlation coefficient between Young's modulus and age (47 to 97 years) was not significant with p = 0.063. Conclusion The zonular system in presbyopic eyes is linear elastic, and the Young's modulus of the zonules decreases 20% from presbyopic age to late presbyopic age. However, there was no significant correlation between Young's modulus and age in presbyopes.

Purpose For the study of the biomechanical properties of lens and zonules in a stretching device, we wanted to investigate the effect of keeping the ciliary body intact or cutting it radially. Methods We studied the anterior eye segment of 3 pairs of presbyopic human donor eyes (ages 51‐85). These segments, comprising of lens, zonules, ciliary body and sclera, were radially stretched in our device which allows force and tissue elongation measurements to be made. First, each pair (OD and OS) was stretched with the ciliary body intact and the lens in place, afterwards, in OD, the ciliary body was cut radially and the lens was kept, and in OS, the ciliary body was kept intact and the lens removed, then we stretched again. Forces are given at 500 µm stretch, measured from lens centre to ciliary body edge. Results The mean force with the ciliary body intact and the lens in place was 74 mN. When the ciliary body was cut (with lens in place) the required force was 35 mN. When the ciliary body was keep intact and the lens removed we measured a force of 47 mN, which represents the contribution of the circumferential stretch of the ciliary body. Conclusion Stretching anterior eye segments showed that the required forces were considerably higher when the ciliary body was kept intact as compared when it was cut radially. These forces were increased due to the circumferential resistance by the ciliary body.

Purpose Amyloid beta, the main protein component of Alzheimer (AD) plaques and tangles, is characterized by high levels of beta‐sheets. Raman microspectroscopy allows quantitative analysis of this specific molecular conformation. We compared the beta‐sheet levels in lens opacities and in plaques and tangles in the hippocampus of AD patients. Methods We obtained 14 lenses from 7 post‐mortem donors , neuropathologically confirmed as having advanced or moderate AD. From 3 of these donors, we also obtained hippocampus tissue. Protein and lipid conformations were analysed in the 500‐1800 cm‐1 fingerprint region. The ratio of the beta‐sheet peak at 1668 cm‐1 and the protein peak at 1450 cm‐1 is a quantitative measure for the beta‐sheet content. Additionally, histological sections were stained using a standard Congo red protocol and amyloid beta immunohistochemistry. Results The 1668cm‐1/1450cm‐1 ratio, quantitatively reflecting the beta‐sheet content, is 1.28 for clear and cataractous regions in the lens.For the plaques and tangles in the hippocampus the ratio is 1.62 and 1.23 for non‐affected regions. When corrected for the presence of lipids in plaques and tangles this ratio is 2.64. Congo red and amyloid beta immunohistochemistry is positive for AD plaques and tangles but is negative for all lenses studied. Conclusion In contrast with a previous study (Goldstein et al. 2003) we conclude that proteins in opaque regions of lenses and in hippocampal plaques and tangles are fully different species. Moreover opacification is not accompanied by changes in the beta‐sheet configuration of lens proteins. This means that cortical cataract cannot be considered as an indicator and predictor of AD.

Purpose Eye lenses from human donors with and without Alzheimer's disease (AD) were studied to evaluate the presence of amyloid in cortical cataract. Methods We obtained 39 lenses from 21 postmortem donors with AD and 15 lenses from age‐matched controls. For 17 donors, AD was clinically diagnosed by general physicians and for 4 donors the AD diagnosis was neuropathologically confirmed. As controls, 7 donors with pronounced cortical opacities and 8 donors with almost transparent lenses were selected. All lenses were photographed in a dark field stereomicroscope. Histological sections were analyzed using a standard and a more sensitive Congo red protocol, thioflavin staining and beta‐amyloid immunohistochemistry. Results Of the 21 donors with AD, 6 had pronounced bilateral cortical lens opacities and 15 only minor or no cortical opacities. Thioflavin, standard and modified Congo red staining were positive in the control brain tissues and in the dystrophic cornea. Beta‐amyloid immunohistochemistry was positive in the brain tissues but not in the cornea sample. Lenses from control and AD donors were, without exception, negative after Congo red, thioflavin, and beta‐amyloid immunohistochemical staining. Conclusion The absence of staining in AD and control lenses with the techniques employed lead us to conclude that there is no beta‐amyloid in lenses from donors with AD or in control cortical cataracts.