Age-dependence of the optomechanical responses of ex vivo human lenses from India and the USA, and the force required to produce these in a lens stretcher: The similarity to in vivo disaccommodation

Abstract

The purpose of this study was to study the age-dependence of the optomechanical properties of human lenses during simulated disaccommodation in a mechanical lens stretcher, designed to determine accommodative forces as a function of stretch distance, to compare the results with in vivo disaccommodation and to examine whether differences exist between eyes harvested in the USA and India. Post-mortem human eyes obtained in the USA (n=46, age = 6 to 83 years) and India (n=91, age = 1 day to 85 years) were mounted in an optomechanical lens stretching system and dissected to expose the lens complete with its accommodating framework, including zonules, ciliary body, anterior vitreous and a segmented rim of sclera. Disaccommodation was simulated through radial stretching of the sectioned globe by 2 mm in increments of 0.25 mm. The load, inner ciliary ring diameter, lens equatorial diameter, central thickness and power were measured at each step. Changes in these parameters were examined as a function of age, as were the dimension/load and power/load responses. Unstretched lens diameter and thickness increased over the whole age range examined and were indistinguishable from those of in vivo lenses as well as those of in vitro lenses freed from zonular attachments. Stretching increased the diameter and decreased the thickness in all lenses examined but the amount of change decreased with age. Unstretched lens power decreased with age and the accommodative amplitude decreased to zero by age 45-50. The load required to produce maximum stretch was independent of age (median 80 mN) whereas the change in lens diameter and power per unit load decreased significantly with age. The age related changes in the properties of human lenses, as observed in the lens stretching device, are similar to those observed in vivo and are consistent with the classical Helmholtz theory of accommodation. The response of lens diameter and power to disaccommodative (stretching) forces decreases with age, consistent with lens nuclear stiffening.

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

“…These optical changes should be the result of geometrical and structural changes of the crystalline lens with accommodation. Changes in lens shape with accommodation were studied in vitro, using stretching devices to mimic the radial accommodative forces, both in human [43][44][45] and nonhuman primates. 34,46 The shift of spherical aberration with accommodation toward more negative values has also been reported in stretching experiments of in vitro human 43 and macaque monkey lenses (Maceo BM, et al IOVS 2013;54:ARVO E-Abstract 4272; and Ref.…”

Change in human lens dimensions, lens refractive index distribution and ciliary body ring diameter with accommodation

“…Table 4 is a summary of changes in lens thickness, lens diameter and ciliary ring diameter for our study and for previous in vivo studies using various methodologies, together with a recent in-vitro study [22]. These changes are given per diopter of accommodation, with some studies using the accommodation stimulus as the measure of accommodation, while others used estimates of accommodation response.…”

“…For the in-vitro study involving lens stretching and laser raytracing [22], the rate of change for lens thickness at + 0.07 mm/D was similar to in-vivo studies, the rate for lens diameter at −0.05 mm/D was at the low end of in-vivo studies, and ciliary ring diameter was much higher than in-vivo studies at 0.16 mm/D. As changes in lens power are about 30% greater than accommodation measured at the front of the eye [23], correction to make them more comparable with the in vivo studies using accommodation response would give respective rates of approximately 0.06, 0.08 and 0.19 mm/D.…”

Deformable Surface Accommodating Intraocular Lens: Second Generation Prototype Design Methodology and Testing

“…The natural force available from the eye's ciliary body muscle contraction and zonular/capsular tension is minimal. 8 Therefore, any design must incorporate a minimal force required to actuate the lens while not exceeding its elastic limits.…”

“…The relaxed tension decreases the pressure and There is a small available force applied by the capsular membrane (~1 g) that must be sufficient to actuate the lens and alter its power sufficiently. 8 The present study examines the ex vivo force requirements and image quality for this type of accommodating intraocular lens. Additionally, factors necessary to optimize the lens efficacy and quality are delineated for future developers and designers of accommodating intraocular lenses.…”