Diffracted-ray approach to the fast evaluation of diffractive lenses

We employ a combination of asymptotic methods to speed up the computation of fields in the focal region of a diffractive lens (DL). The DL is treated locally as a linear grating with a slowly varying period and groove orientation. We employ rigorous electromagnetic diffraction theory locally to obtain the field just behind the DL. A simple diffracted-ray formula is derived for the field in the focal region of the DL at observation points that are not in the immediate vicinity of the optical axis. A careful study of the range of validity of this formula is made. For observation points that are not in the immediate vicinity of the optical axis the new algorithm is 3 x 10(5) times faster than the application of numerical integration to the double integrals involved and approximately 1000-1200 times faster than a recently published algorithm based on using asymptotic theory to replace the double integral with a single integral.

Use of subjective and nonsubjective methodologies to evaluate lens radiation damage in exposed populations--an overview

The general epidemiological acceptability of prevalence, or incidence, for assessing risk of radiation cataract development has dictated an almost exclusive dependence on cataract onset as a measure of cataractogenicity for given doses of radiation. The advent of instrumentation capable of acquiring images amenable to quantitative analyses offers the possibility of exploiting "relative opacification" as an added, if not exclusive, parameter. This development is particularly important in efforts to assess populations such as that in the Altai, which are temporally far removed from their exposure and among whom there exists a large subset with extant cataracts. The new technologies, Scheimpflug and retroillumination imaging, combined with the application of the appropriate analytical algorithms can not only provide quantitative and nonsubjective assessment of lens transparency, but also serve as a means to immortalize the state of the pathology at the time of acquisition. Highly relevant to the assessment of an aging exposed population is the use of lens epithelial fragments as potential dosimeters. The material is routinely available as a result of cataract extraction procedures and is amenable to the application of a modified micronucleus (MN) assay. The MN assay in the lens has tremendous advantages over its use in other tissues for a number of reasons, not least of which is that lens MNs are extremely long-lived. Given the relative ease of application and its potential as a radiation bioindicator, the lens MN assay should be considered in any follow-up of populations exposed to ionizing radiation.