Lens internal curvature effects on age-related eye model and lens paradox

Abstract

Abstract:The gradient index (GRIN) model is the most accurate way to represent the eye lens which, because of its growth mode, is a lamellar, shell-like structure. The GRIN is thought to provide optical properties that counteract age-related changes in curvature that would otherwise create an increasingly myopic eye: the so-called lens paradox. This article investigates how fine-tuning the refractive index and the internal curvatures of the lenticular indicial contours may prevent the ageing eye from becoming myopic. A system matrix approach is applied for analysis of a shell model with 200 shells to obtain the paraxial characteristics of the eye model.

Presbyopia: Effectiveness of correction strategies

“…Although the refractive index of the crystalline lens centre does not change significantly with age (Augusteyn, 2010), the nucleus increases in size with age, causing the gradient between high and low refractive indices to become steeper (Jones et al, 2005;Kasthurirangan et al, 2008), however, the exact shape and location of the gradient remains equivocal (Pierscionek and Regini, 2012). More recently, the gradient index (GRIN) model has been proposed as the most accurate way to represent the crystalline lens with a lamellar, shell-like structure (Giovanzana et al, 2017).…”

Accommodation and age-dependent eye model based on in vivo measurements

“…Thus later authors4, 5 developed new, simplified, eye models to make calculations easier to perform. In contrast, with the availability of computers to speed calculation, other more recent models have often included additional characteristics in order to achieve a better approximation to real eyes, such as: aspheric surfaces6, 7, 8, 9, 10, 11, 12; chromatic dispersion6, 9, 12; intraocular scattering 13 ; changes with accommodation3, 4, 6, 9, 11, 12, 14; and age 7, 11, 15, 16. In the last few years, information produced by new devices capable of taking numerous “ in vivo” clinical measurements of the optical parameters of real eyes has been used by some authors to develop further eye models based on statistical data for the ocular parameters 11, 12, 17, 18, 19…”

Linear optics of the eye and optical systems: a review of methods and applications

“…In the human eye, the GRIN crystalline lens is a combination of radial and linear GRIN systems. The lens is a decreasing GRIN lens, and the refractive index is a function of the transverse ( y ) and longitudinal ( z ) positions, describing a transverse parabolic distribution 8 117. The transference of a GRIN lens will depend on the maximum and minimum refractive indices, age, lens thickness, radii of curvature of the lens and nucleus front- and back-surfaces, number of shells and the power chosen to represent the distribution of the GRIN across a normalised distance 8 117…”

“…The transference is easily obtained for schematic eyes, including the reduced eye, 12 Le Grand’s eye, 13 14 an astigmatic schematic eye 65 105 and an eye with a GRIN lens. 117 One important advantage of linear optics is modelling optical properties to aid understanding of clinical phenomena. For example, linear optics was used to illustrate chromatic aberrations in an astigmatic eye.…”