Case Of Lenses Research Articles

A clinical case of fitting scleral contact lenses for congenital bilateral eyelid coloboma complicated by exposure keratopathy

A clinical case of fitting scleral contact lenses for congenital bilateral eyelid coloboma complicated by exposure keratopathy

Shadowfocimetry: adapting the holographic principle to a manual focimeter for visualization/marking of permanent engravings in progressive addition lenses

Focimeters, especially manual versions, are the most used ophthalmic devices for dioptric power measurement in optometric clinical care. In the particular case of progressive addition lenses (PALs), they are used to determine far/near vision correction powers, but the user/clinician needs to know at which part of the PAL the measurement must be taken. For this reason, PALs have permanent engravings acting as reference marks to define the far/near vision areas for every PAL design. However, for several reasons these engravings are often difficult to localize and identify, making an accurate dioptric power determination difficult. In this Letter, we present an adaptation of the Gabor holographic principle to a manual focimeter and describe the methodology for the correct localization, visualization, and marking process of the reference engravings in PALs. Experimental results considering different types of PALs are included and the main limitations of the technique are also discussed.

ФОРМИРОВАНИЕ ИНТЕНСИВНЫХ ПУЧКОВ ЗАРЯЖЕННЫХ ЧАСТИЦ В ТРАНСАКСИАЛЬНОЙ КАТОДНОЙ ЛИНЗЕ

The paper proposes a method for taking into account the effect of space charge on the quality of focusing of charged particles and investigates the problem of the formation of an intense flux of charged particles using a transaxial cathode lens, which is a special case of cathode lenses with two planes of symmetry. The article solves a self-consistent problem by representing the distribution functions of potentials and space charge in the form of power series in small parameters. The author uses an improved and proven method for studying cathode lenses, based on taking into account the longitudinal component of the total aberration. The necessary equations and formulas are obtained for calculating the parameters and designing a source of charged particles based on a transaxial cathode lens.

A Rare Case Report of Unilateral Twin Crystalline Lenses

We report a rare case of congenital twin crystalline lenses in an eye. The longest visible iris diameter was oblique, drawn from temporal to nasal quadrant making cornea horizontally oval. The crystalline lenses were found to be situated obliquely on the horizontal axis in the upper temporal and lower nasal quadrant.

Detection of Balamuthia mandrillaris DNA in the storage case of contact lenses in Germany.

Acanthamoeba spp. are frequently the etiological agents of a severe form of sight-threatening keratitis, called Acanthamoeba keratitis. The contact lens storage solution of a patient with keratitis of unknown genesis was screened using our diagnostic tools to detect potentially pathogenic free-living amoebae (FLA). Culture methods and a triplex quantitative real-timepolymerase chain reaction (qPCR) targeting Acanthamoeba spp., Naegleria fowleri, and Balamuthia mandrillaris were used in context of this routine screening. While no amoebae were detected by culture, qPCR specifically detected DNA of B. mandrillaris. This FLA is known as the etiological agent of a fatal form of encephalitis in humans and other mammals, Balamuthia amoebic encephalitis (BAE). A fragment of the 18S rDNA gene was amplified from the sample and showed 99% sequence identity to B. mandrillaris sequences from GenBank. To the best of our knowledge, this is the first report of B. mandrillaris found in association with contact lenses. Although no viable amoeba was obtained by culturing efforts, the verification of B. mandrillaris DNA in the contact lens storage solution demonstrates how easily this pathogen might come into close contact with humans.

Microlensing planet detection via geosynchronous and low Earth orbit satellites

Planet detection through microlensing is usually limited by a well-known degeneracy in the Einstein timescale $t_E$, which prevents mass and distance of the lens to be univocally determined. It has been shown that a satellite in geosynchronous orbit could provide masses and distances for most standard planetary events ($t_E \approx 20$ days) via a microlens parallax measurement. This paper extends the analysis to shorter Einstein timescales, $t_E \approx 1$ day, when dealing with the case of Jupiter-mass lenses. We then study the capabilities of a low Earth orbit satellite on even shorter timescales, $t_E \approx 0.1$ days. A Fisher matrix analysis is employed to predict how the 1-$\sigma$ error on parallax depends on $t_E$ and the peak magnification of the microlensing event. It is shown that a geosynchronous satellite could detect parallaxes for Jupiter-mass free floaters and discover planetary systems around very low-mass brown dwarfs. Moreover, a low Earth orbit satellite could lead to the discovery of Earth-mass free-floating planets. Limitations to these results can be the strong requirements on the photometry, the effects of blending, and in the case of the low orbit, the Earth's umbra.

Using Nonprinciple Rays to Form Images in Geometrical Optics

Constructing ray diagrams to locate the image of an object formed by thin lenses and mirrors is a staple of many introductory physics courses at the high school and college levels, and has been the subject of some pedagogy-related articles. Our review of textbooks distributed in the United States suggests that the singular approach involves drawing principle rays to locate an object's image. We were pleasantly surprised to read an article in this journal by Suppapittayaporn et al. in which they use an alternative method to construct rays for thin lenses based on a “tilted principle axis” (TPA). In particular, we were struck by the generality of the approach (a single rule for tracing rays as compared to the typical two or three rules), and how it could help students more easily tackle challenging situations, such as multi-lens systems and occluded lenses, where image construction using principle rays may be impractical. In this paper, we provide simple “proofs” for this alternative approach for the case of thin lenses and single refracting surfaces.

Formalismo óptico matricial e aplicações

O formalismo óptico matricial é desenvolvido a partir da aplicação da lei de Snell para descrever a refração de raios óticos numa superfície esférica. A seguir, dito formalismo é aplicado para achar e justificar parâmetros típicos e expressões como distância focal, condição de imagem e aumento lateral para o caso de uma lente esférica fina imersa em ar. Além disso, é estudado o caso de uma lente esférica fina imersa em dois meios ópticos com índices de refração diferentes e encontrados os parâmetros e expressões correspondentes para este caso.

Resale Price Maintenance after Leegin: The Curious Case of Contact Lenses

Resale price maintenance (RPM) is a controversial pricing practice for managing retail distribution channels. In Leegin Creative Leather Products, Inc. v. PSKS, Inc. (2007), the Supreme Court abolished a nearly century-old per se rule against RPM established in Dr. Miles Medicine Co. v. John D. Park & Sons (1911). Henceforth, RPM will be judged under federal antitrust law by the rule of reason – a less restrictive standard that requires courts to weigh all the relevant circumstances of a case to assess whether a practice unreasonably restrains trade. Despite that the decision in Leegin leaves many unanswered questions, the decision has prompted an increasing number of consumer goods manufacturers to adopt RPM in the management of their retailer relationships. Recently, the widespread use of restrictive pricing practices in the retail distribution of contact lenses have drawn attention and elevated debate over the practice. Pending lawsuits in the industry have been identified as an important “test case” for antitrust’s new vertical pricing regime following Leegin. Drawing upon relevant literatures from law, economics, and business, together with publically available information, important questions in the debate and related cases that share significance for scholarship and practice are elaborated upon and examined. This examination reveals insights helpful to understanding the antitrust implications of contact lens manufacturers’ pricing practices and for advancing academic knowledge, marketing practice, and competition policy involving RPM.AAI Working Papers are typically works in progress that will eventually be revised and published elsewhere. They do not necessarily represent the position of the American Antitrust Institute. This Working Paper represents the work of the authors and does not necessarily represent the views of the American Antitrust Institute or their affiliated institutions.

Numerical implementation of generalized Coddington equations for ophthalmic lens design

A method for general implementation in any software platform of the generalized Coddington equations is presented, developed, and validated within a Matlab environment. The ophthalmic lens design strategy is presented thoroughly, and the basic concepts of generalized ray tracing are introduced. The methodology for ray tracing is shown to include two inter-related processes. Firstly, finite ray tracing is used to provide the main direction of propagation of the considered ray at the incidence point of interest. Afterwards, generalized ray tracing provides the principal curvatures of the local wavefront at that point, and its orientation after being refracted by the lens. The curvature values of the local wavefront are interpreted as the sagital and tangential powers of the lens at the point of interest. The proposed approach is validated using a double-check of the calculated lens performance in the spherical lens case: while finite ray tracing is validated using a commercial ray tracing software, generalized ray tracing is validated using a software application for ophthalmic lens design based on the classical version of Coddington equations. Equations of the complete tracing process are developed in detail for the case of generic astigmatic ophthalmic lenses as an example. Three-dimensional representation of the sagital and tangential powers of the ophthalmic lens at all directions of gaze then becomes possible, and results are presented for lenses with different geometries.

EFFECTIVE MODELS FOR STATISTICAL STUDIES OF GALAXY-SCALE GRAVITATIONAL LENSING

We have worked out simple analytical formulae that accurately approximate the relationship between the position of the source with respect to the lens center and the amplification of the images, hence the lens cross section, for realistic lens profiles. We find that, for essentially the full range of parameters either observationally determined or yielded by numerical simulations, the combination of dark matter and star distribution can be very well described, for lens radii relevant to strong lensing, by a simple power-law whose slope is very weakly dependent on the parameters characterizing the global matter surface density profile and close to isothermal in agreement with direct estimates for individual lens galaxies. Our simple treatment allows an easy insight into the role of the different ingredients that determine the lens cross section and the distribution of gravitational amplifications. They also ease the reconstruction of the lens mass distribution from the observed images and, vice-versa, allow a fast application of ray-tracing techniques to model the effect of lensing on a variety of source structures. The maximum amplification depends primarily on the source size. Amplifications larger than ~20 are indicative of compact source sizes at high-z, in agreement with expectations if galaxies formed most of their stars during the dissipative collapse of cold gas. Our formalism has allowed us to reproduce the counts of strongly lensed galaxies found in the H-ATLAS SDP field. While our analysis is focussed on spherical lenses, we also discuss the effect of ellipticity and the case of late-type lenses (showing why they are much less common, even though late-type galaxies are more numerous). Furthermore we discuss the effect of a cluster halo surrounding the early-type lens and of a supermassive black hole at its center.

Contact Lens Removal

A case of adherent soft contact lenses in an apprehensive adolescent patient is described, along with a description of a novel technique for contact lens removal. After topical anesthesia and saline irrigation, the lenses were successfully removed, atraumatically, using a pair of saline-soaked cotton-tipped applicators held in a chopstick fashion.

Pseudophake und phake torische Linsen zur Korrektur des kornealen Astigmatismus - Theorie und klinische Aspekte

In the last decades the implantation of pseudophakic and phakic toric lenses has become wide-spread for the correction of corneal astigmatism in cases of classical cataract surgery with implantation of a posterior chamber lens or in cases of refractive surgery with implantation of a piggyback lens. The purpose of this review article is to present an en bloc mathematical strategy for calculating pseudophakic and phakic toric lenses and for deriving the spectacle refraction after implantation of an arbitrary lens. We restrict ourselves to a centred coaxial optical system containing spherocylindrical surfaces and interspaces with a homogeneous optical medium. All calculations are done in the paraxial space according to linear Gaussian optics. We define an optical model for the pseudophakic and phakic eye and characterise all known refractive surfaces and interspaces between the surfaces with 4 x 4 refraction and translation matrices, respectively. The entire optical system is described with a 4 x 4 system matrix, which relates the impinging beam (slope angle and height, both in x and y directions) with the exiting beam (slope angle and height, both in x and y directions) and extract the required parameters from the matrix representation. In example 1, we describe step-by-step how to derive a pseudophakic toric lens implant from the biometric parameters and in example 2 we estimate the residual refraction at spectacle plane after implantation of a pseudophakic lens. In example 3, we describe step-by-step how to derive a phakic toric lens implant from the initial refraction and biometric measurements and in example 4 we estimate the residual refraction at spectacle plane after implantation of a phakic lens. The calculation scheme presents a strategy for calculating toric lenses and residual refractions based on a thin lens model of the spectacle correction, the cornea and the lens implant. This model can be generalised easily to a thick lens model, if the appropriate geometric parameters of both lens surfaces are known. The phakic lens calculation can directly be transferred to the case of pseudophakic piggyback lenses.

Geometrical properties of the X-ray diffraction applied to Laue lenses

An analytical study of the geometrical properties of the X-ray diffraction applied to the case of Laue lenses is reported in this paper. The results of this investigation are analytical equations that describe the point in which a photon is diffracted as a function of the crystal position and of the X-ray source angular coordinates. In addition, the contributions to the lens Point Spread Function of each crystal is described, helping in understanding the optical properties of a Laue lens. The results obtained can be inserted in simulation and image deconvolution softwares for speeding up the calculations.

Microlensing modulation by quadrupole variation

We investigate microlensing in the case where the lens is considered as an extended object. We use a multipolar expansion of the lens potential and show that the time-varying nature of the quadrupole contribution allows to separate it from the mass and spin contributions and leads to specific modulations of the amplification signal. As example we study the case of binary system lenses in our galaxy. The modulation is observable if the rotation period of the system is smaller than the time over which the amplification is significant and if the impact parameter of the passing light ray is sufficiently close to the Einstein radius so that the amplification is large. Observations of this modulation can reveal important information on the quadrupole and thus on the gravitational radiation emitted by the binary lens. Even if not observed directly, because of their importance the quadrupole modulation has to be included in the error budget for high magnification ($\ensuremath{\mu}\ensuremath{\le}7$) microlensing events.

Fractal conical lenses

A conical lens is an optical element that produces a continuous focal segment along the optical axis. In this paper we introduce a more general optical device: the fractal conical lens (FCL). As the profile of a FCL is generated using the Cantor function, we show that a classical conical lens is a particular case of these fractal lenses. FCLs are distinguished by the fractal focal segments they produce along the optical axis. The influence of the Fresnel number on the axial irradiance generated by these lenses is investigated.

Emergent innovation systems and the delivery of clinical services: The case of intra-ocular lenses

This paper is an exploration of the dynamics of technical change in medicine. We argue that innovation in medicine is a process that is distributed across time, space and epistemic and institutional domains; that it entails the entrepreneurial effort of creative individuals as well as the emergence of correlated understanding among heterogeneous agents whose rules of interaction are contingently instituted in socio-economic systems along unfolding scientific and technological trajectories. We illustrate our arguments through an in-depth analysis of a major ophthalmologic innovation – the intra-ocular lens – that has literally transformed the treatment of cataract in the developed world and has the potential to do so in many developing countries. We investigate the advancement of clinical knowledge about the disease, the development of effective technological capabilities and the co-evolution of the supply capacity and demand of a micro-innovation system emerged along a specific sequence of interrelated problems, and associated solutions, which engaged scientists, technicians, practitioners, regulators and patients alike over a period of around three decades.

Accretion Disk Structure and Orientation in the Lensed and Microlensed Q0957+561 Quasar

Because quasars are unresolved in optical imaging, their structures must currently be inferred. Gravitational microlensing offers the possibility of producing information about the luminous structure provided that the Einstein ring diameter of the microlensing particle is comparable to or smaller than the radiating quasar components. Particularly interesting is the case of multiple-image gravitational lenses, where differences in the brightness histories of the multiple images can reveal the presence of the microlensing particles and allow inferences about the quasar's structure. The long brightness history measured for the Q0957 quasar has been analyzed previously for information about the microlensing particles, and evidence for the existence of a cosmologically significant population of planetary-mass particles has been reported. The microlensing results have also directly determined the sizes of the ultraviolet light emitting surfaces in the quasar. Autocorrelation analysis of the same brightness record has produced evidence for complex structure in the quasar; if the quasar suddenly brightens today, it is probable that it will brighten again after 129, 190, 540, and 620 days. We interpret these lags as the result of luminous structure around the quasar, and in particular we interpret them in the context of the Elvis model of the quasar's structure. We find that the autocorrelation peaks imply that beyond the luminous inner edge of the accretion disk, the biconic structures of the Elvis model must lie at a radial distance of 2 × 1017 cm from the black hole, and 2 × 1016 cm above and below the plane of the accretion disk. The quasar is apparently inclined 55° to the line of sight. A second possible solution with lower inclination and larger structure is also indicated but statistically less probable.

Velocity Effects on the Deflection of Light by Gravitational Microlenses

We study the influence of general lens and source velocities on the gravitational deflection of light by single and two-point-mass microlenses with general axis orientation. We demonstrate that in all cases the lens equation preserves its form exactly. However, its parameters -- the Einstein radius and the binary-lens separation -- are influenced by the lens velocity. In Galactic microlensing settings the velocity mainly affects the inferred separation for wide binary-star or star+planet microlenses oriented close to the line of sight. We briefly discuss the case of lenses moving with highly relativistic velocities.

Dynamics of Fermat potentials in nonperturbative gravitational lensing

We present a framework, based on the null-surface formulation of general relativity, for discussing the dynamics of Fermat potentials for gravitational lensing in a generic situation without approximations of any kind. Additionally, we derive two lens equations: one for the case of thick compact lenses and the other one for lensing by gravitational waves. These equations in principle generalize the astrophysical scheme for lensing by removing the thin-lens approximation while retaining the weak fields.