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We address the measurement and correction of fan distortion in optical coherence tomography (OCT). This effect arises from the scanning system configuration and prevents one, in general, from obtaining quantitative topographic data from OCT. Computer simulations allowed us to quantify the effect and evaluate its dependence on the scanning mirror separation and design of the collimating lens, as well as to estimate the optimal axial position of that lens to minimize the fan distortion. We also developed a numerical algorithm based on 3-D ray propagation for the correction of the residual fan distortion. The effect was studied experimentally using a custom developed time-domain OCT in a Michelson configuration provided with a confocal channel, and the accuracy of the fan distortion correction algorithm tested on samples of known dimensions (flat surfaces and spherical lenses). With a proper calibration of the system with use of an onfocal channel, this algorithm makes it possible for time-domain OCT devices to be used as topographers. OCIS codes: 110.4500, 120.6650, 120.4640, 110.6880, 330.7327, 330.4300.

A method of ray tracing for free-form optical surfaces has been developed. The ray tracing through such surfaces is based on Delaunay triangulation of the discrete data of the surface and is related to finite-element modeling. Some numerical examples of applications to analytical, noisy, and experimental free-form surfaces (in particular, a corneal topography map) are presented. Ray-tracing results (i.e., spot diagram root-mean-square error) with the new method are in agreement with those obtained using a modal fitting of the surface, for sampling densities higher than 40 x 40 elements. The method competes in flexibility, simplicity, and computing times with standard methods for surface fitting and ray tracing. OCIS codes: 080.1753, 080.2720, 330.7326, 330.4875.

The dynamic changes of the anterior surface of the eye are investigated. A Twyman-Green interferometer is used to record topographic images at 40 ms intervals. A method of analysis of the dynamic changes in topography by use of Zernike polynomials enables a general distinction to be made between dynamic alterations in the shape of the cornea itself and the changes in the layer of the tears. The influence of deviations in the shape of the anterior surface of the eye on the retinal image is estimated. OCIS codes: 120.3180, 330.4460, 330.5370, 110.3000, 170.4470.

Intraocular lenses (IOLs) are used in the cataract treatment for surgical replacement of the opacified crystalline lens. Before being implanted they have to pass the strict quality control to guarantee a good biomechanical stability inside the capsular bag, avoiding the rotation and to provide a good optical quality. The goal of this study was to investigate the influence of the material and haptic design on the behavior of the IOLs under dynamic compression condition. For this purpose, the strain-stress characteristics of the hydrophobic and hydrophilic materials were estimated experimentally. Next, these data were used as the input for a finite-element model (FEM) to analyze the stability of different IOL haptic designs, according to the procedure described by the ISO standards. Finally, the simulations of the effect of IOL tilt and decentration on the optical performance were performed in an eye model using a ray-tracing software. The results suggest the major importance of the haptic design rather than the material on the postoperative behavior of an IOL. FEM appears to be a powerful tool for numerical studies of the biomechanical properties of IOLs and it allows one to help in the design phase to the manufacturers. [ABSTRACT FROM AUTHOR]

Purpose. The aim of the study is to demonstrate that the ocular dynamics of the anterior chamber of the eye can be estimated quantitatively by means of optical coherence tomography (OCT). Methods. A commercial high speed, high resolution optical coherence tomographer was used. The sequences of tomographic images of the iridocorneal angle of three subjects were captured and each image from the sequence was processed in MATLAB environment in order to detect and identify the contours of the cornea and iris.Thedata on pulsatile displacements of the cornea and iris and the changes of the depth of the gap between themwere retrieved from the sequences. Finally, the spectral analysis of the changes of these parameters was performed. Results. The results of the temporal and spectral analysis manifest the ocular microfluctuation that might be associated with breathing (manifested by 0.25Hz peak in the power spectra), heart rate (1-1.5Hz peak), and ocular hemodynamics (3.75-4.5Hz peak). Conclusions. This paper shows that the optical coherence tomography can be used as a tool for noninvasive estimation of the ocular dynamics of the anterior segment of the eye, but its usability in diagnostics of the ocular hemodynamics needs further investigations. [ABSTRACT FROM AUTHOR]

The implantation of an artificial intraocular lens (IOL) into a capsular bag in place of an extracted natural, but nontransparent lens is a standard therapy method in the case of cataract. Any decentration or tilt of the IOL can cause a deterioration of the retinal image quality, thus decreasing the vision quality. The analysis of the relative position of Purkinje images being a reflection of the point light source from the refracting surfaces of the eyeball determines the location of IOL inside the eye and thus enables to state its wrong or correct location. The paper describes the Purkinje experimental setup consisting of an illuminator (several infrared LEDs arranged in a circle), an imaging telecentric lens and image recording CCD camera and reports details of the system calibration The usefulness of the experimental setup has been proven both in laboratory conditions using artificial model of the eyeball and in measurements on human subjects. Simulations of the retinal image with different decentrations or tilts are shown. [ABSTRACT FROM AUTHOR]

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]

Intraocular lens (IOL) is an artificial lens implanted into the eye. It usually replaces the existing crystalline lens, which is clouded over due to a cataract. In order to evaluate the optical performance of different IOLs an optomechanical model of human eye was developed. This model closely reproduces anatomical and optical properties of the average human eye. This makes it possible to measure the optical performance of different types of intraocular lenses and to estimate the influence of their location in eye on quality of vision. Four monofocal intraocular lenses were taken for analysis. The analysis of the quality of retinal images was carried out by means of either qualitative image comparison or physical quantities estimation. The analysis of LSF and MTF shows that the performance of the lenses tested changes slightly with differences in their design and/or material. [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]