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An investigation was carried out with the aim of reconstructing the gradient index (GRIN) profile of human crystalline lenses ex-vivo using optical coherence tomography (OCT) imaging with an optimization technique and to study the dependence of the GRIN profile with age. Cross-sectional images of nine isolated human crystalline lenses with ages ranging from 6 to 72 (post-mortem time 1 to 4 days) were obtained using a custom-made OCT system. Lenses were extracted from whole cadaver globes and placed in a measurement chamber filled with preservation medium (DMEM). Lenses were imaged with the anterior surface up and then flipped over and imaged again, to obtain posterior lens surface profiles both undistorted and distorted by the refraction through the anterior crystalline lens and GRIN. The GRIN distribution of the lens was described with three variables by means of power function, with variables being the nucleus and surface index, and a power coefficient that describes the decay of the refractive index from the nucleus to the surface. An optimization method was used to search for the parameters that produced the best match of the distorted posterior surface. The distorted surface was simulated with accuracy around the resolution of the OCT system (under 15 µm). The reconstructed refractive index values ranged from 1.356 to 1.388 for the surface, and from 1.396 to 1.434 for the nucleus. The power coefficient ranged between 3 and 18. The power coefficient increased significantly with age, at a rate of 0.24 per year. Optical coherence tomography allowed optical, non-invasive measurement of the 2D gradient index profile of the isolated human crystalline lens ex vivo. The age-dependent variation of the changes is consistent with previous data using magnetic resonance imaging, and the progressive formation of a refractive index plateau. [ABSTRACT FROM AUTHOR]

In order to restore clear vision in the case of cataracts the opaque crystalline lens of the diseased eye is extracted and an artificial intraocular lens (IOL) is implanted in its place. Different designs of IOLs are used in practice. The retinal image quality in such an eye (pseudophakic) depends on the parameters of the implanted IOL, in particular on its chromatic aberration. Since the dispersive properties of IOL material differ from that of a crystalline lens, the chromatic aberration of a pseudophakic eye is much greater than in a healthy eye. This paper studies a hybrid (refractive-diffractive) IOL of chromatic aberration chosen in a such way that the overall longitudinal chromatic aberration (LCA) of the pseudophakic eye is equal to that of the healthy eye. Simulated retinal images calculated with the help of typical lens design software ZEMAX® illustrate the usefulness of such a solution. [ABSTRACT FROM AUTHOR]

A model for a gradient index intraocular lens (IOL) is presented. The distribution of the refractive index is Gaussian, varying radially in the equatorial plane and with distance from the optic axis in the sagittal plane. An algorithm for adjustment of the optimal gradient index distribution for individual parameters of a pseudophakic eye is also described. The performance, in terms of spherical aberration and resultant image quality that can be provided with the gradient index IOL, is compared with that provided by a commercially available IOL (Tecnis Z9000). [ABSTRACT FROM AUTHOR]