Biomedical subjects

Eva Acosta

Publications and source records attributed to Eva Acosta.

7 recordsLinked to original sources

PubMed2007

Paraxial optics of astigmatic systems: relations between the wavefront and the ray picture approaches.

PURPOSE: The paraxial propagation of astigmatic wavefronts through astigmatic optical systems can be described by the augmented step-along method (ASAM). Its equivalence to the linear ray optics approach is considered in detail. METHODS: The ASAM is exploited to derive paraxial ray paths through a general coaxial astigmatic system. RESULTS: Starting from the information inherent in the ASAM all 2x2 submatrices rendering the general 4x4 transference of linear optics can be generated. This proves the complete equivalence of both approaches. Additionally, we show that the symplectic relations are automatically obeyed in the ASAM. CONCLUSIONS: The ASAM offers a complete alternative to describe the paraxial optics of astigmatic optical systems. According to the ASAM, an optical system is fully characterized by the back vertex vergence and the angular magnification matrix. Hence, a complete description of the paraxial optics of an eye should not only report the state of refraction but the angular magnification matrix as well, although it is not yet very common. The magnification matrix might be important in cases of anisometropia or the design of progressive addition lenses. Yet, a simple clinical procedure to determine the angular magnification matrix is missing.

Astigmatism↗

PubMed2006

Paraxial propagation of astigmatic wavefronts through noncoaxial astigmatic optical systems.

PURPOSE: The paraxial propagation of astigmatic wavefronts through a noncoaxial system is described. METHODS: The augmented stepalong method (ASAM) for vergences is extended to tilted and decentered elements. RESULTS: Equations for the case of tilted and decentered elements are presented in the framework of vergence calculations. All effects according to the perturbation of a centered system can be derived from the vergences provided by the calculations for the unperturbed system. In particular, the shift in image space rendered by the pertubation is simply the sum of additional decenter and tilt terms to the unperturbed system. CONCLUSIONS: Previous work on the description of the propagation of astigmatic wavefronts has been generalized to noncoaxial systems. This completes the wavefront picture built on the paraxial augmented stepalong method.

Astigmatism↗

PubMed2006

Modified point diffraction interferometer for inspection and evaluation of ophthalmic components.

We demonstrate that a modified point diffraction interferometer can be used to measure the power distribution of different kinds of ophthalmic lenses such as spectacles, rigid and soft contact lenses, progressive lenses, etc. The relationship between the shape of the fringes and the power characteristics of the component being tested is simple and makes the design a very convenient and robust tool for inspection or quality control. Some simulations based on the Fresnel approximation are included.

Journal Article↗

PubMed2006

Tomographic method for measurement of the gradient refractive index of the crystalline lens. II. The rotationally symmetrical lens.

In the first part of this paper we presented a tomographic method to reconstruct the refractive index profile of spherically symmetrical lenses. Here we perform the generalization to lenses that are rotationally symmetrical around the optical axis, as is the ideal human lens. Analysis of the accuracy and versatility of this method is carried out by performing numerical simulations in which different magnitudes of experimental errors and two extreme case scenarios for the likely shape of the refractive index distribution of the human lens are considered. Finally, experimental results for a porcine lens are shown. Conceptually simple and computationally swift, this method could prove to be a valuable tool for the accurate retrieval of the gradient index of a broad spectrum of rotationally symmetrical crystalline lenses.

Animals↗

PubMed2005

Paraxial propagation of astigmatic wavefronts in optical systems by an augmented stepalong method for vergences.

PURPOSE: The propagation of astigmatic wavefronts through astigmatic optical systems is reconsidered in the wavefront perspective. METHODS: The stepalong method for vergences, described by 2x2 matrices, is applied and augmented to produce off-axis information like the magnification. This so-called augmented stepalong method (ASAM) is derived by applying the paraxial propagation of astigmatic wavefronts to tilted wavefronts as well. RESULTS: The features of the ASAM are discussed for a single surface, a thick lens, and a general system. CONCLUSIONS: The ASAM provides all necessary information to describe a centered astigmatic optical system in paraxial approximation.

Astigmatism↗

PubMed2005

Tomographic method for measurement of the gradient refractive index of the crystalline lens. I. The spherical fish lens.

We present an iterative tomographic algorithm to reconstruct refractive-index profiles for meridional planes of the lens of the spherical fish eye from measurements of deflection angles of refracted rays. Numerical simulations show that the algorithm allows accuracy up to the fourth decimal place, provided that the refractive index can be regarded as an analytical function of the radial coordinate and the experimental errors are neglected. An experimental demonstration is given by applying the algorithm to retrieve the refractive-index profile of a spherical fish lens. The method is conceptually simple and does not require matching of the index of the surrounding medium to that of the surface of the lens, and the related iterative algorithm rapidly converges.

Animals↗

PubMed2005

Variable aberration generators using rotated Zernike plates.

The rotational properties of Zernike polynomials allow for an easy generation of variable amounts of aberration using two rotated phase plates, each one encoding one or several Zernike modes. This effect may be used to build variable aberration generators useful for calibrating different kinds of aberrometer.

Journal Article↗